Topic: CB750: Aware of cheap parts -tensioner rubber cracked in 2- Carb boots cracking

[flybox1]

My primary roller is made from the same material from cyclex.  Its holding up nicely.

[Prospect]

Reviving an old thread. I just pulled the engine of my CB 750 to replace the faulty cam chain tensioner. I don't want to make the same mistake twice and buy from a Taiwanese supplier. What is the general consensus regarding where to buy a good tensioner.

[madmtnmotors]

What is the general consensus regarding where to buy a good tensioner.

Honda.

[grcamna2]

How have the aftermarket steel ones been running ?

[Prospect]

What is the general consensus regarding where to buy a good tensioner.

Honda.

Just ordered one from Honda. It wasn't much more than the cheap ones.  Lesson learned.

[madmtnmotors]

What is the general consensus regarding where to buy a good tensioner.

Honda.

Just ordered one from Honda. It wasn't much more than the cheap ones.  Lesson learned.

Amen to that. After sourcing new ones from Honda it was only about $20 more than the aftermarket ones I had used...

and I don't have to tear down the top end before 3000 miles this time!

[HondaMan]

I still have the "test" going with the aftermarket and Honda rollers sitting in some used motor oil (halfway up their diameters) to see if anything shows up: no change yet. It started in May last year. Neither one shows any effect.

[madmtnmotors]

I still have the "test" going with the aftermarket and Honda rollers sitting in some used motor oil (halfway up their diameters) to see if anything shows up: no change yet. It started in May last year. Neither one shows any effect.

I'd be willing to bet it's the stress from the chain on the rollers more than anything else that contributes to the "cheapo" tensioner failing.

[HondaMan]

I still have the "test" going with the aftermarket and Honda rollers sitting in some used motor oil (halfway up their diameters) to see if anything shows up: no change yet. It started in May last year. Neither one shows any effect.

I'd be willing to bet it's the stress from the chain on the rollers more than anything else that contributes to the "cheapo" tensioner failing.

Might be? Their recall notice stated it was due to "..extended exposure to motor oil..." which I can't believe, myself.
What I DID find on every one of the clones was: the notch in the pivot arm that aligns with the tang on the pivot pin had burrs on every one. This prevented the whole arm from freely pivoting as they should. I am beginning to suspect that since none of the engines I rebuilt with them have had any troubles, and since I manually ground/filed/polished this burr off on each one so it would work correctly, this is more likely the cause? I got this habit from not having perfect parts from Honda, either: I even have a tensioner arm of theirs in this test that has a too-tight, frozen, roller.

[Jerry Rxman Griffin aka MuthaF'er]

How do you compare the rubber used in each? Perhaps it's just that simple??

[PeWe]

I still have the "test" going with the aftermarket and Honda rollers sitting in some used motor oil (halfway up their diameters) to see if anything shows up: no change yet. It started in May last year. Neither one shows any effect.

I'd be willing to bet it's the stress from the chain on the rollers more than anything else that contributes to the "cheapo" tensioner failing.

+1
Exposure to oil and heat might help to make the rubber prone to crack when the chain is pressing against the rubber wheel.
That rubber feels different than std Honda, softer. I have the leftovers in my garage together with new Honda tensioner.

I was lucky to find the cracked upper wheel when lifting head. I have probably not noticed it. Maybe metal flakes later on in oil when the upper rubber was completely off, chain against the "hub".

[HondaMan]

I still have the "test" going with the aftermarket and Honda rollers sitting in some used motor oil (halfway up their diameters) to see if anything shows up: no change yet. It started in May last year. Neither one shows any effect.

I'd be willing to bet it's the stress from the chain on the rollers more than anything else that contributes to the "cheapo" tensioner failing.

+1
Exposure to oil and heat might help to make the rubber prone to crack when the chain is pressing against the rubber wheel.
That rubber feels different than std Honda, softer. I have the leftovers in my garage together with new Honda tensioner.

I was lucky to find the cracked upper wheel when lifting head. I have probably not noticed it. Maybe metal flakes later on in oil when the upper rubber was completely off, chain against the "hub".

Yeah, like you say, PeWe: the rubber on the clones is a little bit softer. It feels like it might have less "fiber" in it, or something like that, as it seems to be semi-translucent when held up to a real strong light. The Honda one seems to be more opaque.

There are several other aftermarket ones out there that are made of steel (like the Yosh racing ones) or nylon of some kind. The steel ones were originally reported to have been made to prevent their chipping at constant high RPM in races like Daytona, but were said to be hard on the cam chain itself. That makes sense: the nylon ones came along much later, like in the 1990s, IIRC. At least, I don't remember seeing any of those until then?

[754]

Durometer test for hardness .

[PeWe]

I still have the "test" going with the aftermarket and Honda rollers sitting in some used motor oil (halfway up their diameters) to see if anything shows up: no change yet. It started in May last year. Neither one shows any effect.

I'd be willing to bet it's the stress from the chain on the rollers more than anything else that contributes to the "cheapo" tensioner failing.

+1
Exposure to oil and heat might help to make the rubber prone to crack when the chain is pressing against the rubber wheel.
That rubber feels different than std Honda, softer. I have the leftovers in my garage together with new Honda tensioner.

I was lucky to find the cracked upper wheel when lifting head. I have probably not noticed it. Maybe metal flakes later on in oil when the upper rubber was completely off, chain against the "hub".

Yeah, like you say, PeWe: the rubber on the clones is a little bit softer. It feels like it might have less "fiber" in it, or something like that, as it seems to be semi-translucent when held up to a real strong light. The Honda one seems to be more opaque.

There are several other aftermarket ones out there that are made of steel (like the Yosh racing ones) or nylon of some kind. The steel ones were originally reported to have been made to prevent their chipping at constant high RPM in races like Daytona, but were said to be hard on the cam chain itself. That makes sense: the nylon ones came along much later, like in the 1990s, IIRC. At least, I don't remember seeing any of those until then?

Metal wheels is an alternative too. I tried one setup last season (street bike), the upper wheel with teeth has marks after cam chain. The upper wheel should be better hardened?
I think that I'll go for Honda std this time. The only "problem" is that the rubber hardens during the years and fall into small pieces, found in the oil pump area.

[HondaMan]

I still have the "test" going with the aftermarket and Honda rollers sitting in some used motor oil (halfway up their diameters) to see if anything shows up: no change yet. It started in May last year. Neither one shows any effect.

I'd be willing to bet it's the stress from the chain on the rollers more than anything else that contributes to the "cheapo" tensioner failing.

+1
Exposure to oil and heat might help to make the rubber prone to crack when the chain is pressing against the rubber wheel.
That rubber feels different than std Honda, softer. I have the leftovers in my garage together with new Honda tensioner.

I was lucky to find the cracked upper wheel when lifting head. I have probably not noticed it. Maybe metal flakes later on in oil when the upper rubber was completely off, chain against the "hub".

Yeah, like you say, PeWe: the rubber on the clones is a little bit softer. It feels like it might have less "fiber" in it, or something like that, as it seems to be semi-translucent when held up to a real strong light. The Honda one seems to be more opaque.

There are several other aftermarket ones out there that are made of steel (like the Yosh racing ones) or nylon of some kind. The steel ones were originally reported to have been made to prevent their chipping at constant high RPM in races like Daytona, but were said to be hard on the cam chain itself. That makes sense: the nylon ones came along much later, like in the 1990s, IIRC. At least, I don't remember seeing any of those until then?

Metal wheels is an alternative too. I tried one setup last season (street bike), the upper wheel with teeth has marks after cam chain. The upper wheel should be better hardened?
I think that I'll go for Honda std this time. The only "problem" is that the rubber hardens during the years and fall into small pieces, found in the oil pump area.

One thing I have noticed in all Honda's (and other similar bikes) bikes AFTER the CB750 is: the cam chain tensioners' tensioner rollers all have semi-toothed sprockets on them. These teeth do not fully engage the chain links, but they do guide the chain accurately onto the sprockets. They also usually have bearings (needle or ball type) inside as well, instead of the plain bearing found in this SOHC4 design (and in other Honda Twins of the era): the fancy bearings certainly reduce rolling friction and hence, chain wear or roller stress. I fully suspect that if a metal roller with some sort of bearings were employed in these SOHC4 engines for a long period of time (supposing first that it could be properly oiled) that it would increase the wear on the outer edges of the cam chain links because of the drag and imperfect mating. On the Yosh rollers (only a couple, or a few) that I have seen, the rollers show the witness of this crash, like you describe. Making it harder might make the chain suffer more?

A while back, someone was making ones from nylon or Delrin (or something) and selling them on eBay. If the right kind of nylon, and a proper bearing installation was accomplished in the center, I suspect this could be a good substitute, as nylons like Polypenco, teflon, and others have high fibrous strength and are naturally slippery (and oil resistant). Has anyone here tried one of those, and then taken it apart after a while to see how it is doing?

I have about a dozen worn ones, which could supply "parts" for a rebuildable kit of some kind, supposing the nylon version works out well. If so, it is mighty tempting to start making such a kit, like Elan makes oil pump parts.

[754]

I am thinking some oils affect them. More than others..
Anyone with chunkng or flaking, let us know what oil you are running..

[markreimer]

So the failure has always been the roller rivited into the metal body?

I rebuild my 750 top end a couple months back, maybe 400km on it since. I ordered the large roller from Cycle-X, they list it as genuine "straight from Honda" on their site. I forgot to order the smaller wheel/metal body assembly  so just reused that piece. Silly because that's the one that tends to wear more.  Must've ordered that really late at night, or really early in the morning hah.

Hopefully mine is ok.

I'll also add that I have some of the cheap $45 carb boots (eBay purchase I think) and I've been having a real weird stumble/gurgle when cruising mid-RPM. Just recently noticed at least one of my boots has a huge slash in it running from the end, under the band clamp. I didn't even bother checking the others, just parked the bike and ordered legit Honda ones from Partzilla. Waiting for them to arrive now.

lesson learned....Honda parts only whenever there's the option.

Oh, but unlike others, I haven't had an issue with my cruizin image carb kit for my 350F.. except for the float bowl gaskets, They didn't come close to fitting.

[jebon]

I use simple 2x11 or 2x12 O-rings, available everywhere. This issue comes up if you have a pre-1973 cylinder, which does not use the long rubber seals in the studs' holes, and a post-1972 head gasket with the big holes. Otherwise, you can just get the right head gasket with the small holes, instead.

Do you have a good p/n for the head gasket with the smaller holes?

When looking for the gasket (or kits) with the smaller holes, choose those listed as for "1969-1972" engines, as opposed to the others. That's the primary difference between the kits.

I have a pre 72 cylinder and seller sent me a later Vesrah kit with the big holes, saying it was fine to use. Will this work for me or should I get the earlier one with small holes?

[HondaMan]

I use simple 2x11 or 2x12 O-rings, available everywhere. This issue comes up if you have a pre-1973 cylinder, which does not use the long rubber seals in the studs' holes, and a post-1972 head gasket with the big holes. Otherwise, you can just get the right head gasket with the small holes, instead.

Do you have a good p/n for the head gasket with the smaller holes?

When looking for the gasket (or kits) with the smaller holes, choose those listed as for "1969-1972" engines, as opposed to the others. That's the primary difference between the kits.

I have a pre 72 cylinder and seller sent me a later Vesrah kit with the big holes, saying it was fine to use. Will this work for me or should I get the earlier one with small holes?

You can use the one with the larger holes, but I recommend inserting O-rings (2x12 or 2x13) into each of those 8 holes to ensure no oil weepage. PM me with your address if you need some of these: I probably have 100 of them, still. For a while we were getting the "big hole" headgaskets in the Vesrah kits, and when they got smarter (2004 or so) they went back to making an early version (VG-156) and the later version (VG-157) kits.

[johno]

What a great thread !
I recently purchased some parts from CI and 2 parts in particular stood out to me.
How BAD was the cam tensioner, rubber quality /  wheel roller burred. 🤬. in BIN.
How GOOD were the 65mm pistons.  checked thoroughly , dimensions, ring lands, weights, dome thickness etc nice pistolies.😁🏁👍

Just my 2 cents worth to the topic.
cheers Johno

[MauiK3]

How did anyone do work on stuff like this before great forums like this one could be joined?

[HondaMan]

How did anyone do work on stuff like this before great forums like this one could be joined?

My sentiments, exactly!
It was partly the reason my shop became so 'famous' back in the day of these bikes, too. We did it right (inspected by me if I didn't do it myself) every time. The one time we didn't was while I was in Final Exams week and a new hire changed the tranny oil (unsupervised) on a new GT550 Suzy he had bought a month earlier: the new kid drained the oil, didn't put any in, and the store manager, during the mechanic's lunch break, gave the bike back to the customer - who lived 50 miles away! Needless to say, I made the manager pay for a new transmission for that poor guy's bike: I wanted him to replace the bike, but he didn't have the $$.

AFAIK that was the only major mistake my shop ever made.