CB350 oil transfer piece - with pictures (also applies to CB250)

[crazypj]

Hi all,
Was sent a set of 350 carbs to modify plus, the oil filter cover.
Actually took measurements of this one as the clearance between sliding oil transfer piece and delivery to filter seemed smaller than usual?
Anyway, oil delivery hole to centrifugal filter varies between 0.250" and 0.280" (over 0.3 sq in area)
The 'return' clearance between inlet pipe is only about 0.030" with two guide bars on the spring loaded piece. It worked out around 0.075" sq area or, one quarter of the inlet side.
No wonder cam bearings fail at high rpm.
I've done a LOT of work on the pieces with carbide burr's plus a diamond burr as the material of transfer piece seems much harder than the 360 one?
Some pics.
about 90% finished, forgot to get a 'start' picture
DSCN7732.jpg
The external and internal guide posts
DSCN7733.jpg
Used a 3/32" carbide ball end burr to cut channels into delivery pipe.(this is checking at 90% done, I tidied the channel up as pic below)
It's about as deep as the circlip groove (0.365")
DSCN7734.jpg
Second channel 180 degrees away from first one .
Channels are 90 degrees to the guide posts.
DSCN7736.jpg DSCN7735.jpg
The inner bore of transfer piece was ground out so there is 1mm 'ledge' for the spring to sit on. It was opened up around 0.025" each side except next to the guide posts where I uses a 1/16" diamond burr to change radius slightly and went 0.030" larger)
The very top coil of spring was opened up slightly to be an interference fit inside the transfer piece, initially there was about 0.015" clearance which limited how far the ID could be opened (needed a bigger ledge for spring to sit on)
The new ID varies between 0.545" and 0.530", thicker at centre as there is less support than at guide posts.
Original ID was about0.470 " with the delivery pipe at about 0.410"
DSCN7737.jpg
The exact same process should be done on any Honda that uses transfer piece, 175 to CB500T.
Early bikes are much easier to do as the cover is a separate part so you don't need to be working down a hole like 360's

Almost forgot, it should be obvious but make sure the circlip 'gap' isn't lined up with the guide bar. Use a small screwdriver or similar to make sure it's lined up 90 degrees to them

[LongDistanceRider]

Thanks for the write up PJ.
Moved to the Technical section under Tips and Tricks with a redirect from the 350 Engine section

[crazypj]

Thanks, I was wondering where I should put it,

[ancientdad]

Almost forgot, it should be obvious but make sure the circlip 'gap' isn't lined up with the guide bar. Use a small screwdriver or similar to make sure it's lined up 90 degrees to them

And if you're doing a DOHC 450 or 500T, this is also important. Be sure to get the tangs on the valve (shown by the red arrow in the first picture) back in the intended "holes" in the cover (red arrows in the second picture) before putting the snap ring back in place or the valve will be allowed to turn and move around and intermittently alter oil flow. The top end of the engine is what suffers, specifically the left exhaust cam bearing and left exhaust cam lobe and follower.





BTW, this could be the result if you don't. Don't ask me how I know.

[crazypj]

I can't remember what, but one of the Honda's has asymmetric guides so it only 'slides' when assembled one way.
I had forgotten about 450/500 as I haven't done any major work on one since about 1979

[Mikepacific60]

Hi Crazypj,
Any tips on how to remove the spring wire circlip holding the pieces in place….I had a go at getting mine out but have given up for the moment (I didn’t want to scratch up the shaft butchering around with small screwdrivers etc).
Also, please excuse my basic question, but what is this mod actually doing (I guess my issue is that I don’t have a good understanding of how the oil flow is managed after the pump) ie what does this part actually do and what does the mod achieve?
Cheers
Mike

[crazypj]

Removing the wire clip is probably the hardest part of this mod.
I've tried lots of different methods and cheap circlip pliers (the ones with replaceable tips) are one of the 'easiest' methods (but still not real easy)
I've tried straight and 90 degree bend tips to open clip enough to get a small screwdriver under one edge then pry up.
It's really frustrating when clip falls back into place more times than you want to count but eventually it will come off.
The reason for mod is the oil flow is severely restricted by the difference in area between 'inlet' side of filter and 'outlet side of filter.
The inlet side is a hole about 6mm dia which gives an area of about 28 sq mm. The outlet is only about 0.75 sq mm which is 'adequate' for low rpm but at high rpm, the oil pressure and flow increases enough to push on the transfer piece, compress spring and dump most of the oil directly back to sump. The mains and big ends still get enough oil from splash lubrication but there isn't' anything' going up the studs to cam bearings, which, being plain bearings, need a constant oil supply. It doesn't take long for cam bearings and rocker arms to wear and often seized bearings result.
Asa it only happens at sustained high rpm it isn't normally a problem but I've seen way too many engines with failed cams over the years.
Honda knew it was a problem so when they designed CB250/360, they gave it an uprated oil pump which made things MUCH worse as transfer piece 'opened' at much lower rpm.
Before I figured out the 'cure' I had more than one engine fail at very low miles (between 70~100 miles at 70mph)
After I did the first or second motor, never had a failure plus, stripping one that had been a bit 'abused'( red-lined pretty much everywhere for 2,000+ miles) the rocker pads actually looked more polished than when I fitted them
. Using 5W-30 full synthetic probably helped as well (I was pretty paranoid about cam area)
Since then, I've 'refined' the mod slightly to get maximum flow without compromising transfer piece, going much further could possibly weaken it allowing it to jamb or break which would be a REALLY BAD THING

[Mikepacific60]

Hi to all (& especially crazypj),
Thanks heaps for taking the time to explain what’s going on here.
I think I now have a handle on how this all works….
- the oil pump pumps the oil through the pipe in the cover (ie on the SL350K1 the one held on by three screws);
- the oil flows into the filter where centrifugal force pushes rubbish to the edges of the filter bowl;
- the oil exits the bowl around the edges of the transfer piece - therein lies the problem…there isn’t much room around the edges of the transfer piece for the oil to travel and when the pressure gets high (at high revs) the spring in the transfers piece compresses and oil is dumped into the sump, starving the top end;
- the solution is to increase the area around the transfer piece to allow better flow of oil to the top end at high revs.

Correct?

What tricked me up a bit was the oil both entering and exiting the oil pump through the transfer piece…it seemed to me there would be a fair bit of oil just flowing back out of the filter housing without being spun to remove debris. No doubt Honda was satisfied that the oil would be filtered well enough using this system…

And persistence did pay off (I mucked around with the poor condition engine piece) and did get off the tricky spring circlip. I also noticed a decent burr on the end of the pipe, so chamfered that off. Now to re-read the instructions above about performing the mod….I certainly take the point about not taking too much meat off the pipe…would be a disaster if that broke off while the engine was running!
3AF04EDA-948E-4B26-8611-61455009364F.jpg

Cheers
Mike

[Mikepacific60]

More on this….
As I mentioned above, I’ve disassembled the oil transfer pieces.

The ID of the transfer piece from this newer engine is around 0.515” (larger than the unmodified piece at 0.470” mentioned by crazypj in the first post above):
342B3340-7552-41C6-A26F-7C0AE1C92F77.jpg

Given the existing ID of this piece, should I work to slightly increase the ID?

My above comments relate to the pieces off my later engine….I’m yet to check the dimensions of pieces in my original engine - I’d rather use the original transfer pieces as the one in the pictures looks awful on the outside, with the area where the screws go being very rough…

As an aside, I have a brand new transfer piece…its ID is also approx 0.514”
Cheers
Mike

[Mikepacific60]

Hi crazypj
I’ve had a go at the part from my other engine…how does this look - it’s a fiddly task and not easy to get a neat finish - self evident looking at my work! (looks a bit deep…didn’t notice that until I looked at the photo):
E32CEC67-D752-4A13-BF6E-71D3C58A0540.jpg
I also had a go at the steel transfer piece….look okay?
15F021AF-676D-462C-BA17-F2101C2B13B1.jpg
Cheers
Mike

[crazypj]

Hi Mike, didn't realise you had added to this thread, found you real easy though.
Anyway, looks good to me. I check by assembling without the circlip and check transfer piece doesn't stick (it will if you don't push dead square, even when not modified)
Carbide burr in Dremel doesn't leave best finish and even the Chinese diamond burrs don't get things a whole lot better. That transfer piece is damn hard stuff.
I ended up using a x10 loupe to see what I was doing, don't download and enlarge the pictures I posted too much or you'll see mine are no better.
Very interesting to see Honda had enlarged the ID, it can still be opened up a little though as production tolerances mean it has to be strong enough to be assembled by a 'line worker' who may not be too careful when on piece work? (more of a problem in late 70's when a new bike was coming 'out the door ' every 7 seconds)
Oh, your assumption of operation is correct. The inner pipe delivers oil inside filter where it has to be centrifuged before it exits. Even at 10~15PSI it probably hits end of crank before getting turned around to exit. It's what makes a centrifugal filter so much better than a paper one at removing 'everything' heavy . The fact they centrifuge blood to separate red and white cells should tell people something about efficiency of the process

[Ribrickulous]

The fact they centrifuge blood to separate red and white cells should tell people something about efficiency of the process

And the centrifuges for blood run less than 4,000rpm. Let the engine rev!


-Ed
1972 CL350

[crazypj]

I did not know that and assumed they spun around 10,000 rpm

[Ribrickulous]

Looking further at it, diameter of the rotor comes into play also, which makes sense.

https://www.researchgate.net/post/Wh...ree_hemoglobin

So we may get overall less force from our filters, but the difference in density of oil and metal particles must help us out? Then again the dwell time in the filter is probably significantly less than in a blood centrifuge.

Who knows. It works.


-Ed
1972 CL350

[Mikepacific60]

Thanks heaps everyone,
I worked to get the circlip off my ‘good’ engine transfer piece…boy, what a fight that circlip put up (tougher than the first, dummy run, one) - you need three hands to do that job (+ the somewhat reluctant help of my wife).
I ended up getting it off…talk about blood flowing…I got careless / frustrated with a sharp probe while pushing on the circlip and stabbed myself (doing exactly opposite what I tell my son…ie don’t push / cut toward yourself).
Anyway, onward & upward,
Mike

[Mikepacific60]

More…
Been looking carefully at the aluminium sidecover housing containing the oil transfer piece.
I have noticed the outward flow of oil must get into a chamber which is only about 120 degrees of the total area - that chamber leads into the oil output channel. See my two photos below…the first showing the area I mean (12 o’clock in the photo) and a close up of the area:
BB17F6FD-2612-4012-9D73-5B72F19E42A8.jpg8555BC3F-2F5A-4FE0-9753-BB4B731CFBF5.jpeg

While oil comes out of 360 degrees of the transfer piece - it must all get into the top chamber in the photo (ie the about 120 degree area) to then flow into the oil outward passageway.
Seems to me it would be great to be able to open up a passage between the two ribs to allow oil to flow freely into the collection area (ie into the 120 degree area at the top where the outward passage is) as the oil that goes into the other areas must then flow over the top of the rib to get to the collection chamber. There’s no way to get a drill down into that tiny section, so not possible to drill holes as mentioned above.
Seems it would be good when modifying the inwards pipe to make sure one of the channels you dremmel into the tube aligns with the top oil collection chamber mentioned above.
Apologies if I haven’t explained this too well…easy for me as I have the pieces right in front of me!
Appreciate any comments (even negative ones) about my thoughts above.
And by the way, crazypj is right about the oil transfer piece…it’s made of a very hard metal!
Cheers
Mike

[ancientdad]

I've limited my modifications in this area to opening up the transfer piece. I'm not going to attempt to improve any further on what Honda did, these things worked for decades even without any modification and I just don't feel comfortable taking chances with overdoing something or making a change that might have negative effects, I've already spent too much on replacement parts.

[Mikepacific60]

Hi ancientdad,
Yep, I understand- I gather you stopped short of modifying the alloy delivery pipe…(it is a bit fiddly to work on, and the consequences of a stuff up are not great, ie a whole new alloy piece would be needed which I don’t think are available).
Cheers
Mike

[LongDistanceRider]

It appears that the 2 ribs in question are recessed a bit to start with so maybe a very small grinding bit could be used to lower them some more. Very steady hand and magnifying glasses needed.

[crazypj]

You don't need to get at the 'ribs' down inside, the transfer piece is somewhat 'hollow' so oil can flow into the back of it and get through to the outlet hole.
Somewhat tortuous route but any improvement will help.
The 450/500T doesn't suffer as badly as the smaller engines as it isn't usually held at such high RPM for as long as the smaller ones.
Probably the worst of the lot is the 250 variant of the 360 engine (CB/CJ250) as the smaller bore (56mm) with large ports and carbs (same as 360) has to be kept at high rpm.
The CB/CD 175 has a plunger oil pump that while isn't as efficient as the trochoidal in 250/360 motors still has cam oiling issues as it's possible to run motor 'flat out' if in company with larger bikes (my very first cam seize was on a 1968 CD175) Managed to get it unstuck but the left big end also got 'taken out - 130 miles from home)
I just followed link for blood centrifuge then next link for 'calculator.
At 8,000rpm with a 48mm 'oil cup', you get 3441g which I'm pretty sure will fling everything solid onto sides of 'cup'? (and why build up is so 'hard' and dry?)
Maybe they are no longer used because centrifugal filters at very high rpm are too effective and could 'damage' modern blends of ouil?

[Ribrickulous]

I just followed link for blood centrifuge then next link for 'calculator.
At 8,000rpm with a 48mm 'oil cup', you get 3441g which I'm pretty sure will fling everything solid onto sides of 'cup'? (and why build up is so 'hard' and dry?)
Maybe they are no longer used because centrifugal filters at very high rpm are too effective and could 'damage' modern blends of ouil?

That’s uh. A lot of g’s.


-Ed
1972 CL350

[ancientdad]

Wow, I would never have thought the centrifugal force was that extreme. No wonder it works as well as it does. And all the younger crowd pooh-poohs our old technology...

[Richard Pitman]

This thread is both interesting and worrying. How have my 175 engines survived so long, especially my first brand new one, which was thrashed unmercifully from cold starts on treacle thick 20/50 Castrol GTX car oil ? 22k on the clock when I traded it in, still running fine.

I'd love to see some detailed photos of this modification specifically on the175 parts, very tempted to have a go at it. I have the larger CB200 pump in one engine, which might actually make the situation worse at high rpm, if I've read this correctly.

[crazypj]

Unfortunately I don't have a lot of experience with CB175/200 as shop didn't sell a lot of them.
The CD175's were a better seller for the 'ride to work' crowd and rarely got thrashed and I seem to remember we actually sold about 3:1 MZ 250's over 175's (that's another story,500 mile first service changing main bearings and all the oil seals)

[CatMan]

OK, now that I have read this thread for about the 10th time now, and am sitting here with the parts in front of me (yes I am the kind that needs hands on to comprehend LOL) I am ready to attempt this mod/upgrade, using the parts off of the "spare" engine. Thank you PJ and Mike

[Mikepacific60]

Good luck with it…takes perseverance to get that circlip thing off!!
Cheers
Mike

[CatMan]

Good luck with it…takes perseverance to get that circlip thing off!!
Cheers
Mike

With about 6 try's and 1 beer I got the circlip off
100_4074.jpg
As you can see I screwed the cover to the workbench. Used my circlip pliers to push the ciclip back enough to get my handy-dandy walnut pick into to hold it back. Then used my modified small flat tip to pry the circlip off the rest of the way. No way of taking pictures while trying to do this.

[Mikepacific60]

Hi CatMan,
Glad you got it off…like your idea of screwing the whole piece to the bench…if I ever do this job again I’ll do that.
Cheers
Mike

[ancientdad]

With about 6 try's and 1 beer I got the circlip off

As you can see I screwed the cover to the workbench. Used my circlip pliers to push the ciclip back enough to get my handy-dandy walnut pick into to hold it back. Then used my modified small flat tip to pry the circlip off the rest of the way. No way of taking pictures while trying to do this.

Creative thinking, screwing the cover down to hold it still. Sharing stuff like this is why forums like ours work so well, contrary to modern popular belief. That deserved a second (or third) celebratory beer at least.

[CatMan]

Creative thinking, screwing the cover down to hold it still. Sharing stuff like this is why forums like ours work so well, contrary to modern popular belief. That deserved a second (or third) celebratory beer at least.

That's what makes this a great forum. I have learned a lot here about this 71 CL, and many of the other Honda classics (never too old to learn). Believe me I had a couple more once the clip was off. That's why I stopped at just getting everything apart

[frankjames1900]

The motor that I'm assembling currently is stock. I haven't had problems in the past. ( that I know of yet ) . I usually run mine between 5 and 7 thousand rpms. Is this something that I should look at doing to this motor. ?

[ancientdad]

The motor that I'm assembling currently is stock. I haven't had problems in the past. ( that I know of yet ) . I usually run mine between 5 and 7 thousand rpms. Is this something that I should look at doing to this motor. ?

Frank, it isn't something required per se, it's just another enhancement that you can do to help improve oil delivery and thus long term health if you chose to do it. I ran hundreds, probably close to 1000, WFO 1/4 mile runs on my old 450 drag bike back in the '70s before I ever knew about this mod and it was the old 4 speed bottom end with the 16mm piston oil pump, not even the later 5 speed 19mm piston pump, and it lasted just fine.

[frankjames1900]

Frank, it isn't something required per se, it's just another enhancement that you can do to help improve oil delivery and thus long term health if you chose to do it. I ran hundreds, probably close to 1000, WFO 1/4 mile runs on my old 450 drag bike back in the '70s before I ever knew about this mod and it was the old 4 speed bottom end with the 16mm piston oil pump, not even the later 5 speed 19mm piston pump, and it lasted just fine.

Thanks for your insight. Experience means a lot. I've ran the daylights out of a good few bikes also in my days. Some seemed indestructible, others didn't look very good in the end. That was all before I knew any better. I'll never know why they gave out. It couldn't have been abuse on my part. I found this thread interesting so I thought I would ask. I think it is something that I'll consider doing on the high performance engine before I install it in the bike.
Thanks again.

[frankjames1900]

Oh. Also I will screw it down to the bench. !

[CatMan]

Got the mod done. Not pretty but definitely can see how this will help
100_4079.jpg
Will do better on the next one

[CatMan]

Oh. Also I will screw it down to the bench. !

It helps

[CatMan]

Pics of stock and modified cover/transfer piece.
100_4085.jpg
Stock on the left, mod on the right. Can definitely see how this will help with oil flow
Thanks again PJ

[ancientdad]

Pics of stock and modified cover/transfer piece.

Stock on the left, mod on the right. Can definitely see how this will help with oil flow
Thanks again PJ

Looks good. I might enhance the mod on mine next time I have the filter cover off.

[Mikepacific60]

And here is a picture of mine….bit more conservative than CatMan with respect to the amount of material removed, but I think the engine will still benefit from this mod (and I have no desire to ever remove / reattach that circlip!):
FF681882-2712-40BB-A8C1-5BD9ADA690EF.jpg

I feel CatMan, ancientdad, frankjames1900, crazypj, LongDistanceRider and myself (sure there are others) are members of a very exclusive club…those who have done the “oil transfer mod” :)

Here is an interesting observation….not all of the circular sidecover pieces are the same (the part that is held to the sidecover by three screws)…in the picture by CatMan you can see the casting around the oil outflow hole has a strange extra bit in the casting (this is the same as the SL350K1) - at about 12 o’clock in my photo above.
The outflow hole in the piece looks like this:
6986931E-8774-4614-B258-9A6F0B98ADF7.jpg
I’ve worked out this is so Honda could use this cover on both the CB350 and others like the SL350K1. They did this as the oil passage in the sidecases of these engines are in different places and by slotting the outflow hole, it will align with the sidecover of either engine. I worked this out when I was contemplating buying a Cappellini replaceable paper filter system. In the end this system cannot be used on my SL350K1 as the oil outlet hole in the Cappellini unit doesn’t line up with the oil passage in the sidecover. It would have been a total disaster as there would have been zero oil flow around the engine.
To add some clarity, here is a photo of a CB350 piece where you can see the extra casting bit isn’t there…
00F5B9A0-4182-4D79-8AA0-21E6E904C4D2.jpg
So, be careful if swapping these parts….I believe the one with the extra casting is universal, the one without is not.
Cheers
Mike

[ancientdad]

When you think about how many modern bikes are out there compared to vintage Hondas (twins or otherwise), we're already in a much smaller fraternity that is somewhat exclusive as it is. Interesting difference in the covers you pointed out, I've never had the two side by side to compare. In fact, I had both of my SL350K1s such a short amount of time that I never pulled the oil filter cover anyway (but that was back when one was bought new and the other less than 2 years old)