Issue After Cam Chain Tensioning & Valve Clearance Setting

[GlynnJ]

I have a problem!

The bike is fairly new to me. The engine ran and pulled OK, but the top end was noisy so I decided to adjust the valves. I found the relevant video on Common Motor Collective and I believe I followed it correctly, starting with the cam chain tension adjustment. After that adjustment the engine turned over freely by hand and could be turned in either direction. So I proceeded to adjust the left hand inlet & exhaust valves.

Having finished the left hand side I rotated the engine to get to the T mark on compression stroke of the right cylinder and adjusted the valve clearances. In each case, left & right, I checked the clearances with a 0.003@ feeler gauge after tightening the locking nut and the 'feel' was fine.

I then proceeded to turn the engine over by hand in the correct direction and after about a quarter turn I reached a hard stop. I turned back in the other direction and noted that the exhaust camshaft didn't immediately turn and then there was a clicking noise. The cam chain is now loose!

What have I done? Can I fix it without stripping down the engine? I would swear that I followed the video instructions correctly. I am wondering if the right side valves were previously set loose for a reason...

I am not an expert mechanic by any means, but I have worked on engines for years, including ones much bigger and more complex than this. This is the first time I have encountered this type of issue.

 

[ancientdad]

Despite everything we have said here about not following instructions in videos online, particularly from that source as they so often disregard the FSM believing they know better than the manufacturer that won world GP racing titles year after year before most of them were even born, somehow we still can't convince members to come here first and ask questions before they do something on the DOHC 450 that they've never done before.

Obviously, because we couldn't look over your shoulder to see what you really did as you've described above, it's impossible to say just what you might have done that derailed the results. Since you somehow arrived at a point that seems to be a piston hitting a valve - though it's difficult to be sure - the only conclusion I can come to is that you did the cam chain adjustment incorrectly and then when you rotated the engine one of the cams jumped a tooth or two in its timing to the crankshaft.

 

[GlynnJ]

I guess I am guilty as charged, though I wasn't aware of the issue with "those" videos. I am a recent member and haven't read any posts that contain warnings. My bad. I understand that I have incurred your wrath, so maybe that's me consigned the the naughty step forever? Sorry.

FWIW, the method I used to adjust the cam chain tension was the same is that described in the Clymer manual. Is that incorrect too?

Crankshaft was rotated to TDC LT mark on compression stroke on left cylinder and then turned a further 90 degrees. I confirmed that all valves were closed before I loosened the locknut and bolt, waited a moment and then re-tightened. The cam chain seemed to be correctly tensioned when I had finished and was still so after several rotations of the crankshaft.

At the point where the crankshaft stops rotating, there is no piston/valve contact, though I realise that doesn't mean the cam chain hasn't jumped a tooth or two. I am thinking that maybe the cam chain tensioner wasn't installed correctly by the previous owner and the chain is actually jamming against it, it having been disturbed when it was 'adjusted'. The current issue only occurred after the RH valves were adjusted (and the gaps were very large before I adjusted them).

 

[ancientdad]

After watching the video you referenced, I wonder if one aspect of it (which is dead wrong) isn't what might have happened to you.

Starting at the 4:21 mark, you see him loosen the lock nut on the tensioner lock bolt. Notice that the lock bolt did not turn when he did that, and keep that in mind. He then loosens the lock bolt and for whatever reason, unscrews it about 3/4 of the way to full removal. The lock bolt only has to be loosened about one full turn to provide clearance for the tensioner push bar to use the spring tension on it to move the tensioner roller toward the chain to tension the chain properly. However, when he re-tightens the lock bolt he leaves it finger tight and then tightens the lock nut. This does NOT accomplish locking the tensioner push bar which, under the force of the cam opening a valve will resist with pressure on the cam chain which, in turn, will try to push the cam chain tensioner roller back against the tensioner push bar. If the lock bolt is only finger tight it can, and likely will, push backwards allowing slack in the cam chain and might actually get stuck on the slight ridges the lock bolt creates in the flat surface of the tensioner push bar where the lock bolt is supposed to actually lock it to hold the adjustment.

If you directly followed every single step as he described AND showed in the video, it's possible that some unintended slack in the cam chain caused by the lock bolt not being properly tightened to retain the tensioner push bar's position could have allowed the chain to jump a tooth or two on the crankshaft sprocket.

In addition, before I stopped watching it (which came none too soon) I also watched him describe the index marks on the eccentric adjuster shafts and how they should be oriented, but without describing WHY they should never be facing toward the spark plugs. The truth of the matter, which is something that often escapes these guys like the factory valve adjustment clearance being "too tight", is that the incorrect position of the index mark includes the movement of the tip of the follower almost off the top of the valve stem. This can cause undue wear on the follower and valve stem tip requiring more repairs down the road.

 

[ancientdad]

I guess I am guilty as charged, though I wasn't aware of the issue with "those" videos. I am a recent member and haven't read any posts that contain warnings. My bad. I understand that I have incurred your wrath, so maybe that's me consigned the the naughty step forever? Sorry.

I wouldn't describe it as "wrath", rather my intense desire to ensure every single member who owns a DOHC 450 or 500T gets the correct information and advice, and when I see these @#$%&s telling people absolutely wrong information, or only part of the correct story, or failing to fully describe things properly it causes me to be angry because they have built a Pied Piper following ONLY because watching videos is so in vogue now regardless whether the viewer has a clue if the information is correct or not, and then they blindly follow it all while praising the source for being so genius.

FWIW, the method I used to adjust the cam chain tension was the same is that described in the Clymer manual. Is that incorrect too?

I have no idea if the Clymer-described method is correct, I never read their manuals because they too are not always accurate. And because we have the FSMs available for free download, just as the "geniuses" at CMC do yet they somehow choose to differ with the engineers who designed and built these bikes 50 years ago.

It's just hard for me to understand why someone would join this or any forum and not look around for all the resources that are readily available, particularly in the section for the bike they own. We have worked very hard to right the wrongs about these bikes in this internet-informed world and have taken the time to assemble as many tutorials here as we can to help, but if no one looks for that information nor asks if it's here then we can't help.

 

[GlynnJ]

After watching the video you referenced, I wonder if one aspect of it (which is dead wrong) isn't what might have happened to you.

Starting at the 4:21 mark, you see him loosen the lock nut on the tensioner lock bolt. Notice that the lock bolt did not turn when he did that, and keep that in mind. He then loosens the lock bolt and for whatever reason, unscrews it about 3/4 of the way to full removal. The lock bolt only has to be loosened about one full turn to provide clearance for the tensioner push bar to use the spring tension on it to move the tensioner roller toward the chain to tension the chain properly. However, when he re-tightens the lock bolt he leaves it finger tight and then tightens the lock nut. This does NOT accomplish locking the tensioner push bar which, under the force of the cam opening a valve will resist with pressure on the cam chain which, in turn, will try to push the cam chain tensioner roller back against the tensioner push bar. If the lock bolt is only finger tight it can, and likely will, push backwards allowing slack in the cam chain and might actually get stuck on the slight ridges the lock bolt creates in the flat surface of the tensioner push bar where the lock bolt is supposed to actually lock it to hold the adjustment.

If you directly followed every single step as he described AND showed in the video, it's possible that some unintended slack in the cam chain caused by the lock bolt not being properly tightened to retain the tensioner push bar's position could have allowed the chain to jump a tooth or two on the crankshaft sprocket.

Thank you. I didn't follow the video religiously, but I probably did loosen the screw more than necessary before re-tightening. I didn't leave the bolt only finger tight, but maybe loosening the bolt too much caused an issue.

 

[ancientdad]

Thank you. I didn't follow the video religiously, but I probably did loosen the screw more than necessary before re-tightening. I didn't leave the bolt only finger tight, but maybe loosening the bolt too much caused an issue.

Not likely, and I'm glad you actually re-tightened the lock bolt. This is just one of many examples of the little things they leave out or do wrong that can be the undoing of many a rookie vintage Honda twin owner, yet they act as if they are the go-to for all knowledge about them.

As for what actually happened to your engine, I have no idea at this point. I do know that had you started a thread for the tune-up and posted that you were about to do it and if there were any recommendations, along with plenty of pictures along the way, you might not be in this spot right now. We will do whatever we can to help you, but please get your information here.

 

[GlynnJ]

Not likely, and I'm glad you actually re-tightened the lock bolt. This is just one of many examples of the little things they leave out or do wrong that can be the undoing of many a rookie vintage Honda twin owner, yet they act as if they are the go-to for all knowledge about them.

As for what actually happened to your engine, I have no idea at this point. I do know that had you started a thread for the tune-up and posted that you were about to do it and if there were any recommendations, along with plenty of pictures along the way, you might not be in this spot right now. We will do whatever we can to help you, but please get your information here.

Thank you.

BTW, I did look at the FSM (kindly supplied via this forum) but it doesn't say much about the cam chain adjustment on Page 12, apart from telling you to slacken and re-tighten the bolt. That is what I did.

I will leave things for a day or two (so I can calm down) and will consider what to do next.

 

[ancientdad]

Thank you.

BTW, I did look at the FSM (kindly supplied via this forum) but it doesn't say much about the cam chain adjustment on Page 12, apart from telling you to slacken and re-tighten the bolt. That is what I did.

I will leave things for a day or two (so I can calm down) and will consider what to do next.

Yes, the FSM is lacking in some details which is why we like to add our personal experiences to the mix to help supplement what was left out. We believe the FSMs were written that way in part because they were never intended for public use, only for their dealership techs, many of whom went to Honda's factory schools for 2 weeks or more. Unfortunately I wasn't one of those lucky ones, in part because the dealers I worked for typically sent their fastest mechanics and I was always the slowest but with the lowest comeback rate. I was just a good study during my years at the shops and because I was a young man, I can still recall most everything I learned then by listening, watching and doing.

 

[12ozPBR]

For what it is worth, on many of the old Hondas twins I’ve worked on (both 350 and 450) the cam chain tensioner plunger usually needs to be taken off the bike and completely disassembled in order to function properly. I have found that simply loosening the the locking bolt and nut as described in any manual and assuming the plunger moves to be inadequate. Unless it is grossly out of adjustment you never notice any movement nor hear a “snap” as it tightens. After 40 some odd years they are usually stuck and do not move especially if the bike has set up for a period of time. It’s better to remove the entire assembly and clean it verifying that it moves properly.

 

[GaryJames]

12ozPBR,
Amen to your comments . I have just been through this with my CB350 K4 tensioner...
Check out my latest post on : "down to the bones.." in projects.

I was paranoid about getting it back on the bike properly I finger locked the shaft so the impact plate was just protruding from the tension housing where I could see it.
Then offering it up to the hole at the back so I could see the plate engage with the chain tensioner wheel plate correctly.
After fitting then I went through the adjustment as per the CB350 sticky for adjustment.
Makes it difficult to get the first two bolts starting to thread as you have to push against the spring tension but at least I am happy it is fitted right now.
My shaft was stuck in the tension tube and I don't think is was doing much tensioning.
I had some noise emanating from high up when the bike was warm. I suspect it was the cam chain rubbing on some part of the head slot it runs in.
I won't know for sure until tomorrow weather permitting.

Gary

 

[76Twin]

I'll second taking the tensioner off and disassemble. On all of the 450 and 500T models I have worked on the tensioners were pretty much stuck until I removed, disassembled, and cleaned them thoroughly.

 

[ancientdad]

^^^BUT, do NOT rotate the engine while the cam chain tensioner is removed.

 

[GlynnJ]

Thanks for all the contributions so far. I think the tensioner is the first port of call. Warnings noted!

 

[ancientdad]

Any progress on your situation?

 

[GlynnJ]

Any progress on your situation?

Thanks for asking. No, I haven’t investigated further yet. But I have noticed damage to the left hand spark plug thread in the cylinder head which makes me think I should bite the bullet and remove the head. I can then get the thread repaired and have a better look at the internals.

I also noticed that the rivet link on the cam chain isn’t particularly well riveted, so another reason to dig deeper.

It’s likely to turn into a winter project as the weather is good here and best spent riding other bikes while I have chance. Plenty of cold dark evenings to come.

 

[ancientdad]

Thanks for asking. No, I haven’t investigated further yet. But I have noticed damage to the left hand spark plug thread in the cylinder head which makes me think I should bite the bullet and remove the head. I can then get the thread repaired and have a better look at the internals.

I also noticed that the rivet link on the cam chain isn’t particularly well riveted, so another reason to dig deeper.

It’s likely to turn into a winter project as the weather is good here and best spent riding other bikes while I have chance. Plenty of cold dark evenings to come.

Understood, best to ride while the weather allows since you have other bikes. What happened might be a blessing in disguise based on the things you just mentioned, the damage would have been a lot worse if something had come apart while riding. I agree it would be wise to pull the top end apart later so you can address all the needs properly.

We'll be here when the time comes, ready to help in whatever way we can. If this is your first DOHC 450, here are a few links in case you haven't seen them.

https://www.vintagehondatwins.com/f...ngine-disassembly-help-PLEASE-READ-THIS-FIRST

https://www.vintagehondatwins.com/f...mportant-DOHC-450-and-500T-warmup-information

https://www.vintagehondatwins.com/forums/showthread.php?6319-DOHC-450-500T-head-assembly

And the engine portions of this thread might interest you as well

https://www.vintagehondatwins.com/f...4-CL450-project-reboot-street-legal-this-time

 

[GlynnJ]

Thanks again. I really do appreciate the advice and resources available. I’ll be sure to read the information before I begin and seek help if I’m unsure.

 

[jensen]

including ones much bigger and more complex than this

Never under-estimate the complexity of these engines, nothing to do with their size, but everything to do with the small details en complex dis- and assembly procedures.

 

[GlynnJ]

Never under-estimate the complexity of these engines, nothing to do with their size, but everything to do with the small details en complex dis- and assembly procedures.

True

 

[ancientdad]

True

And to Jensen's point, particularly assembly procedures which can be as complex as any engine you'd find from that era.

 

[jensen]

yes, and the difference to other engines in that era is the way the valves are operated

 

[ancientdad]

yes, and the difference to other engines in that era is the way the valves are operated

Absolutely, because it's the only engine in which Honda ever used torsion bars and to my knowledge, no other manufacturer was bold enough to try something that different, especially that long ago.

 

[ancientdad]

True

Any progress?

 

[GlynnJ]

Any progress?

Not beyond obtaining a full gasket set in anticipation of things to come. I’ll be sure to let you know once I get started. That will be after I’ve spent time reading the manual and the multitude of tips on this forum.

Cheers

 

[GlynnJ]

Hello again, it's been a while.

Over the winter I removed the cylinder head because the LH plug thread needed repair (it was damaged when I bought the bike, though I didn't realise). Given that the head was coming off, it gave me a chance to look at the various components on the cam chain's route around the engine. I did not remove the cams, I just looked at the various "rollers". I discovered that the toothed sprocket on front roller guide was quite badly worn and one of the two plastic rollers was seized, and so I have replaced it, together with the cam chain.

I have now reassembled the engine, having followed the instructions given in Ancientdad's thread regarding the valve timing and all has gone smoothly, but... the valve timing isn't perfect. When the crankshaft is set it LT (left piston at TDC) and the exhaust camshaft is aligned perfectly with its mark, the inlet camshaft is out by a small amount, as shown in the photos. This is with the master link inserted, but not staked, and without having rotated the crankshaft. The cam chain tensioner is applied and the cam chain seems evenly tensioned front & back.

Is this amount of 'error' in alignment acceptable? I am asking before doing anything else...

 

[ancientdad]

Glad you found the issues with the guide rollers and sprocket before running it. The intake mark appears to be less than one tooth off, and both marks not always perfectly dead-on. Have you tried moving the intake cam one tooth the other direction to see if it looks closer? Otherwise I'd say it's as close as you'll get it.

 

[GlynnJ]

Glad you found the issues with the guide rollers and sprocket before running it. The intake mark appears to be less than one tooth off, and both marks not always perfectly dead-on. Have you tried moving the intake cam one tooth the other direction to see if it looks closer? Otherwise I'd say it's as close as you'll get it.

Thanks. I tried one tooth along and the result is below. It looks like it's half a tooth either way. HOWEVER, the first photo in the thread above was with the camshaft in a 'neutral' position whereas in the one below there is torque on the camshaft cause by resistance from the torsion bars. I'm thinking this latter case is better?

 

[ancientdad]

Assuming you're connecting the cam chain on the intake side as recommended, the intake cam needs to be levered into position to reach the mark because at LT it is beginning to open the intake valve on the right cylinder, so that would be a typical result. In this case the intake cam is a half tooth advanced. Either way should run fine, there might be a slight difference in performance in either case but not likely one you'd notice. I'd stake the link and then carefully rotate it a few full revolutions to be sure, but it should be fine. If for whatever reason you encounter a point of any resistance, do not force past it.

 

[GlynnJ]

Assuming you're connecting the cam chain on the intake side as recommended, the intake cam needs to be levered into position to reach the mark because at LT it is beginning to open the intake valve on the right cylinder, so that would be a typical result. In this case the intake cam is a half tooth advanced. Either way should run fine, there might be a slight difference in performance in either case but not likely one you'd notice. I'd stake the link and then carefully rotate it a few full revolutions to be sure, but it should be fine. If for whatever reason you encounter a point of any resistance, do not force past it.

Yes, seems logical. Thank you.

What’s the recommended way to stake the pins? I don’t really want to use an improvised anvil, hammer and punch. The only chain rivet tool I have is too big. Maybe a bicycle chain tool would work.

 

[ancientdad]

What’s the recommended way to stake the pins? I don’t really want to use an improvised anvil, hammer and punch. The only chain rivet tool I have is too big. Maybe a bicycle chain tool would work.

Honestly, the anvil/hammer/punch method works really well if you have a helper who can hold the anvil (a 2 lb hammer works just fine). But, I've used the Stockton chain tool to mushroom the rivet-ends of the link as well, though not the intended way because the tip of the tool (intended for both breaking a link and riveting a link) bent the first time I used it to break a link. So I used a different tip that came with the set and ground it to fit the rivet-ends of the link pins.

 

[crazypj]

And to Jensen's point, particularly assembly procedures which can be as complex as any engine you'd find from that era.

Dunno, I think it's one of the most complicated engines, far more so than any DOHC inline four (except Yamaha EXUP with multi piece head/cambox/bucket guide or possibly the CBX750 with hydraulic tappets)
I sold all my 450/500T stuff years ago as I never thought I would use it again.
Four pound 'lump hammer' and ball pein work fine for riveting, you can use a pin punch but that needs a second person to help out holding lump hammer (drilling hammer for you heathens in USA)
Bicycle chain breaker will work after modification but isn't really strong enough to get more than one or two uses before it breaks

 

[EzPete]

Yes, seems logical. Thank you.

What’s the recommended way to stake the pins? I don’t really want to use an improvised anvil, hammer and punch. The only chain rivet tool I have is too big. Maybe a bicycle chain tool would work.

If you’ve never done the “punch” method for something as small as a cam chain, I’d drop the $20 on an Amazon or HF chain tool. It’ll probably save you a ton of time and aggravation for the few times you’ll need it.

 

[GlynnJ]

Thanks all. I managed using a punch and anvil. Engine rotates without interference so fingers crossed that all is well.

I need to wait until a friend can help me out the engine back in the frame before I know if all is well. Meantime I’ll be checking the valve clearances again.

 

[Richard Pitman]

Late to the party as usual, but this is the tool I used to stake my rivet links. I ground down one of the extractor pins, this would only last for a couple of rivets before needed to be ground down again.

 

[jensen]

I happen to have the original Honda tool for that, came in a box of Honda tools I got from a friend.

 

[ancientdad]

Late to the party as usual, but this is the tool I used to stake my rivet links. I ground down one of the extractor pins, this would only last for a couple of rivets before needed to be ground down again.

That looks just like the sad Stockton tool I bought back in 2016, not knowing what a piece of crap it really was. I've since modified one of the larger pins for staking and it's adequate. But seeing the prices today - and what has gone down in price in the last 3 years anyway - it must have gotten around what a poor tool it is because now you can buy one for less than 1/3 of what I paid.

 

[Richard Pitman]

Actually, that chain tool works perfectly well when used as designed, rather than used as shown in my improvised modification. I've used it to rivet several 'O' rings quite successfully, on my Hornet and on a friends VFR800. On both bikes the chain can be removed and refitted unbroken, ( some dismantling required on the Hornet ) so tool can be used mounted in a vice. If money was no object, and I mounted chains regularly, I'd buy a Whale tool.

 

[GlynnJ]

Just putting this thread to bed (from my perspective).

I got the cam chain link riveted without issue. Once the engine had been rotated a few revolutions, the valve timing marks are very close. I adjusted the valve clearances and then, with some effort, reinstalled the engine into the frame.

The bike started after a few attempts, but is running rich at idle and also the revs are hanging at about 3000. Clearly, the carbs need looking at (again) but also, I suspect, the auto-advance needs attention. Fortunately I have found a thread on here which deals with the auto-advance and so, after checking the static ignition timing and, possibly, running a timing light, I will delve further into the advance mechanism.

It never rains, but it pours! I look forward to the chance to actually ride the bike this summer. Fortunately, I have two other bikes to fall back on...

Thanks to everyone who contributed to this thread. Your help is very much appreciated.

 

[ancientdad]

Just putting this thread to bed (from my perspective).

I got the cam chain link riveted without issue. Once the engine had been rotated a few revolutions, the valve timing marks are very close. I adjusted the valve clearances and then, with some effort, reinstalled the engine into the frame.

The bike started after a few attempts, but is running rich at idle and also the revs are hanging at about 3000. Clearly, the carbs need looking at (again) but also, I suspect, the auto-advance needs attention. Fortunately I have found a thread on here which deals with the auto-advance and so, after checking the static ignition timing and, possibly, running a timing light, I will delve further into the advance mechanism.

It never rains, but it pours! I look forward to the chance to actually ride the bike this summer. Fortunately, I have two other bikes to fall back on...

Thanks to everyone who contributed to this thread. Your help is very much appreciated.

Keep us posted on what you find, I suspect the advance if you feel fairly confident of the carbs at this point. Good to hear the engine is running again.

 

[stl360+450]

You mentioned adjusting valves, but not the timing before starting it up. I would definitely adjust the static timing to see if it improves, but inspecting and cleaning the advancer is a good idea, too.

 

[ballbearian]

+++ on dynamic timing with a strobe, especially with advancer concerns.

 

[GlynnJ]

Keep us posted on what you find, I suspect the advance if you feel fairly confident of the carbs at this point. Good to hear the engine is running again.

I pulled the auto-advance this morning and gave it a thorough clean, not that it was very dirty. Now lubed and reassembled (but not on the bike) and there is maybe a 25 thou gap between cam and 'cam follower rubber thingy' before the springs start to be tensioned. Is that acceptable, or should I try to shorten a spring?

 

[ancientdad]

No free movement of the weights is acceptable, every bit of movement of the weights should be controlled by the springs and the weights should return fully each and every time they move outward. What many here have done is snip off the loop at one end of each spring, then bend the last coil down and make a new loop from it. Go one coil at a time until you get complete return each time the weights move, and with a very slight tension on them at rest.