CL175 has had a rattle noise for a while now. I thought it was my tach rattling at first but realized its actually coming from the engine. Its hard to get audio of it cause it seems most prominent while riding and under load. Its also not super loud compared to engine noise so not sure if it would come through well. Anyway it behaves very specifically so maybe someone could identify some possibilies just by description. Its mid range freq rattle, absent at 1/8th throttle, but if I crack it open just a little more the rattle kicks in and stays consistent throughout the rest of the throttle range. It seems most prominent at lower rpms, but that could just be because the engine noise starts to drown it out past 6k and I don't notice it as much. So the fact that its not there at 1/8th throttle but then kicks in with more throttle indicates its a function of power/load or else vibration. Cam chain and valves are adjusted correctly. Would crank bearings or transmission bearings going bad behave like that? I've never experienced bearings going bad so I wouldn't know what that would sound like. Other than that maybe something with the cam chain tensioner?
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Engine rattle noise under load
- Thread starter tmross
- Start date
mike in idaho
Veteran Member
Maybe detonation and/or pre-ignition from too much spark advance, too lean mixture, or too-hot spark plug heat range. Pull the plugs and look for signs of overheating at the tip.
Ok so I think this vid above is pretty close to the rattle I'm hearing. From this thread https://www.vintagehondatwins.com/forums/threads/cb160-engine-noise-at-around-3000rpm.9888/
Looks like the culprit was worn big end bearings, he replaced the crank and noise went away
mike in idaho
Veteran Member
That video sounds more like something rattling externally, air cleaner cover, stuff in the toolbox? . Big end bearing or piston slap noise should show up at idle. A couple of quick up and down revs, off idle, you should hear the rod knocking.
OMF
Well-known Member
Could it be excessive cam endplay?
stl360+450
Veteran Member
tried to record it today, couldn't get it. just doesn't translate, just sounds like mic distortion or static.
best way to describe it is it has the timbre/freq of a frog croak. a mid range croaky rattle.
most noticeable 4-6k.
absent <1/4 throttle. then absent again past 1/2 throttle. its a function of throttle.
can't hear it stationary. even tried putting it in gear on center stand and can't hear it, has to be moving under load.
Is any of that consistent with excessive camshaft end play? I actually haven't ever seen anyone describe what excessive cam endplay sounds like, nor have I seen anyone capture audio of it, despite much discussion of checking clearance etc.
best way to describe it is it has the timbre/freq of a frog croak. a mid range croaky rattle.
most noticeable 4-6k.
absent <1/4 throttle. then absent again past 1/2 throttle. its a function of throttle.
can't hear it stationary. even tried putting it in gear on center stand and can't hear it, has to be moving under load.
Is any of that consistent with excessive camshaft end play? I actually haven't ever seen anyone describe what excessive cam endplay sounds like, nor have I seen anyone capture audio of it, despite much discussion of checking clearance etc.
Have you taken the points cover off and watched the end of the camshaft at that rpm? Seems like if there's enough movement to make noise, it should be visible.
I did and didn't see any movement.
If you can't see any visual movement then I'd be surprised if that's what's causing the noise.
Clutch rattle?
yeah, also seems weird that it doesn't rattle stationary... like I wouldnt think itd make any difference to the cam whether the trans is in gear/under load or not. maybe i'm wrong. the forces acting on the crank would be different tho.
RobMan
Veteran Member
Vehicle noise is funny how it travels and sounds like it is coming from one place when originating somewhere totally different so sometimes very hard to diagnose. I would really recommend triple checking anything that could possibly be vibrating under the tank or around the gauges. Check the drive chain, sprockets and covers. Had a bad noise on the S90 that I thought was the engine coming apart and found the screws holding the front sprocket cover was lose and the cover was causing the noise. Locktite solved the problem.
You know, since you mention the drive chain... I noticed there is a little bit of a click noise at the front sprocket when turning the rear wheel by hand, the chain isn't tracking perfectly smooth. The slack is adjusted correctly, relatively new chain. Thats worth investigating. Rear wheel might not be aligned straight, need to find a way to dial that in, the marks on the swingarm never seemed accurate.
RobMan
Veteran Member
I quit depending on the swing arm marks other than for rough alignment back when I got my Sportster in 1982. The method I use ( if I am confident the frame is straight and the engine is mounted properly) is to get it close by the marks then I center the teeth of the rear sprocket in the chain rollers as I am spinning the rear wheel. I am sure others might disagree with this method but has worked well for me.
Messed around with chain and rear wheel, I don't think thats causing the noise. Really sounds like engine internal.
Is there a way to verify that? Like is it some sort of excess clearance with the clutch basket or something I can measure or investigate?
I've pulled this engine and got these measurements:
cam endplay: .65mm
big end side clearance: L: .2mm; R: .3mm (std value: .07-.33mm; limit: .6mm)
So big end numbers are in spec, the cam endplay seems excessive though. The 175 doesn't list this spec, the 350 manual lists .2-.6mm std value. There is also this thread where someone had about the same endplay measurement as me and was able to bring it down to .3-.4mm by using thinner end cap gaskets. I think I may go this route.
The only other thing I found is an ever so slight, almost undetectable bit of play in the wrist pins/small ends. Should there be 0 play here? These wrist pins came with the new IMD pistons I installed last year.
cam endplay: .65mm
big end side clearance: L: .2mm; R: .3mm (std value: .07-.33mm; limit: .6mm)
So big end numbers are in spec, the cam endplay seems excessive though. The 175 doesn't list this spec, the 350 manual lists .2-.6mm std value. There is also this thread where someone had about the same endplay measurement as me and was able to bring it down to .3-.4mm by using thinner end cap gaskets. I think I may go this route.
The only other thing I found is an ever so slight, almost undetectable bit of play in the wrist pins/small ends. Should there be 0 play here? These wrist pins came with the new IMD pistons I installed last year.
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Wristpins should have a minute amount of clearance, not sure if the small end rod measurement spec is in the FSM but they ride on a film of oil delivered upward by the notches on the sides of the big end of the rod to help cool the pistons and keep the small end lubed. I've seen some wristpins with somewhat loose fit in the small end that never made any appreciable noise, so the cam end play might be the more likely source.
Aside from pulling the engine to investigate the rattle noise, I'm also looking for cause of low compression (low 130s both cylinders). Some background - I replaced the head earlier this year cause the original one was damaged. The new head I had the valve seats recut, the valves are sealing perfect via leak test. The cylinders were rebored, new pistons/rings last year as well, so I was surprised to see such low compression, and noticeably lower power than before I replaced the head. A leakdown test showed over 20% loss in psi in both cylinders. So when I tore the top end down again a few days ago the first thing I noticed were the compression ring gaps in the R cylinder were lined up, and the ring gaps in the L cylinder were very close to being lined up. Thats not how they were when I assembled the cylinder last time. I rechecked the valve seals and ring gap sizes and everything is in order. The only culprit for compression loss I found was those lined up ring gaps. But I'm not so sure about that, I thought it was scientifically proven that rings rotate freely, sometimes multiple revolutions per minute. The low comp numbers remained consistent ever since I replaced the head. The rings would've had to have settled permanently alligned, seems weird. Naturally I'm still suspicious of something going on with the new head since that was the variable that changed from the last rebuild. Worn valve guides or something like that?
P.S. when the machinist recut the valve seats he said he wouldn't be able to do it if the valve guides were worn. But I dropped the head off with him and he indeed recut the seats, so I'm assuming he determined they were good enough for him to do what he needed to do, though I didn't ask him explicitly.
P.S. when the machinist recut the valve seats he said he wouldn't be able to do it if the valve guides were worn. But I dropped the head off with him and he indeed recut the seats, so I'm assuming he determined they were good enough for him to do what he needed to do, though I didn't ask him explicitly.
Interesting that he didn't mention it despite cutting the seats. I wonder if he had an employee do the work but didn't check the guides himself, or if he told the employee to check the guides prior but that person didn't. Have you tried a different compression gauge? And the obvious but necessary question, throttle wide open and choke off during your testing?
Your clutch plates or steels could be below tolerance, or there could even be too few plates in there.
CB750 came with a clutch rattle that was remedied by adding another plate.
CB750 came with a clutch rattle that was remedied by adding another plate.
stl360+450
Veteran Member
Did you already check the ring end gaps after taking the top end apart? Sorry if I forgot and you already did this.
On my CB750F2, I have noticed that pulling in the clutch reduces the clutch rattle, which is a useful way to confirm that the noise is related to the clutch
What I was getting at is I'm pretty sure the machinist did verify the guides were fine, otherwise he wouldn't have proceeded with the work. I don't think he has an employee under him. I did use multiple different comp gauges actually, the one I trust the most is the Lisle and it read low 130s. My other cheap chinese one read even lower than that, but it always read low. And yes throttle open/choke off.
Yes and they are in spec, this rebore/new top end only has like 2k miles on it so far.
Buy anyway, has anyone ever seen ring gaps just line up like that and stay that way? Everyone always makes a big fuss about ensuring the gaps are spaced apart during reassembly but I'm not actually finding many (any?) real world examples of gaps lining up and causing actual issues...
On the other hand what are the chances I open this engine up and all the ring gaps are aligned like they were.
crazypj
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Listened to it multiple times, take off valve covers and check lock nuts are tight, look inside valve caps for signs of adjuster hitting cap
Maybe cam chain adjuster sticking and something else going on?
I hear three different 'odd' noises.
I rarely bother any more to '120 degree' rings, they rotate at different rates so will line up sometimes, other times exact 'book' spacing but you never know it.
At one time I did it 'religiously', including 3 spacing's on oil rings, never found any difference in performance, oil use, ring wear or fuel 'economy'
The valve seats were cut '3 angle'?
Honda specified that since S65 in 1965.
It may be a good idea to check for valve sticking or springs upside down/missing spring seat washers.
I've seen experienced mechanics fit springs upside down (plus refuse to fix it)
Maybe cam chain adjuster sticking and something else going on?
I hear three different 'odd' noises.
I rarely bother any more to '120 degree' rings, they rotate at different rates so will line up sometimes, other times exact 'book' spacing but you never know it.
At one time I did it 'religiously', including 3 spacing's on oil rings, never found any difference in performance, oil use, ring wear or fuel 'economy'
The valve seats were cut '3 angle'?
Honda specified that since S65 in 1965.
It may be a good idea to check for valve sticking or springs upside down/missing spring seat washers.
I've seen experienced mechanics fit springs upside down (plus refuse to fix it)
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stl360+450
Veteran Member
I thought some about this and one possible explanation would be that the cylinder bores are oval shaped. The ring gaps in a circular bore have no bias in terms of orientation and tend to migrate as the motor runs. If there is an orientation where a ring can release some tension, then it may tend to stay in that position. I guess the gap would likely line up with one of flatter sides of the oval.
Seats were cut 3 angle yes.
I don't think the 175 valve springs have any particular orientation, there is no tighter wound side. I know there is on the 350. I double checked the 175 manual and there is no mention of installing the springs facing any particular way. No missing components either.
crazypj
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Even with dual wound springs there is no mention of correct orientation in any of the service manuals.
I'm not even sure where it is in the general service manual that most people don't even know about (gives various procedures common to all Honda's and saved adding another ~100+ pages to each)
I haven't had a 175 in pieces since about 1977, I'm sure I've forgotten a lot of stuff about them.
I'm not even sure where it is in the general service manual that most people don't even know about (gives various procedures common to all Honda's and saved adding another ~100+ pages to each)
I haven't had a 175 in pieces since about 1977, I'm sure I've forgotten a lot of stuff about them.
I think I might've figured out why bike ran with less power with new head. I put the old head and new head side by side to compare the valve seats. The fresh cut valve seats look different, different angles. The shop didn't know how to do this right. I don't want to take this to another general shop, is there a shop in US that with people experienced with 70s honda twins that could redo this anyone recommends?
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