Author Topic: CB750: Aware of cheap parts -tensioner rubber cracked in 2- Carb boots cracking  (Read 48515 times)

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Offline AshimotoK0

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I have two (not fitted yet) David Silver sourced, ---312---  style cam chain rollers for CB750/CB350K (same part) I got with the P suffix (means pattern). I am going to get the standard ASTM rubber testing for swell / hardness change done on them over the next month or so and have the polymer type analysed. They should be extended grade Nitrile rubber ( not sure if this is BUNA-N) in the States. Will report my findings but it's gonna be a couple of months.
DS will not give me any tech info on them ... says it's the IP of the supplier and hes sold lots and had no complaints.

cheers ... Ash
“Alright friends, you have seen the heavy groups, now you will see morning maniac music. Believe me, yeah. It’s a new dawn.”

Offline Jerry Rxman Griffin aka MuthaF'er

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Harsh,

I was curious about your O-rings. Looked up the part number and it didn't lead anywhere. What's the story on these? Are these the square O-rings? Can you post up the schematic you have on these?
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline millla03

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So the issue has just been with the tensioners from vintageCB750? The big (lower) tensioner roller in my bike is from CB750supply and was labelled as having been made in Japan. Upper tensioner assembly is OEM so I may have dodged a bullet there. Been a couple years and about 10,000 miles since they were installed and haven't had any noticeable issues. But now I'm paranoid...
Luke

72 Honda CB750 K2
78 BMW R100/7
83 Honda Nighthawk 650
07 Honda Rebel 250

Offline Harsh

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Harsh,

I was curious about your O-rings. Looked up the part number and it didn't lead anywhere. What's the story on these? Are these the square O-rings? Can you post up the schematic you have on these?

I guess early s/n engines didn't use the knock pins and the heads weren't machined for them either.  Mine is a K4, but I don't know if it applied to earlier years.  I found this link that has a pic of one of them with some measurements.  They are square cut o-rings.  The service bulletin section here no longer works so I can't pull up the info.  However, I think I saved it on my other computer.

http://forums.sohc4.net/index.php/topic,134095.25.html

Offline Harsh

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Found my printed copy of HSB #42  Hopefully the pics of it are sufficient.

don't worry about the p/n hand written on it.  I wrote that for something else.


Offline Prospect

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I received three emails today from VintageCB750.  The first was a refund of $87.95 to my paypal account.  The second was a $50 gift certificate.  At this point I was thinking a scam of some sort trying to get me to click the links in the emails and login to my account so they could get my password and fleece my account.  Then I received the third one titled Important Safety Notice.  Within the email they stated that their records showed that on April 30, 2012 I purchased a cam chain tensioner set and that they have had issues with the parts supplied.

I received the same refund and gift certificate today. The email also stated that they will file and notice with Transport Canada about these subpar parts. I really didn't want to take the engine apart but I guess I have to. I just have so many projects right now this is the last thing I need.

Current Bikes

1969 CB750  Sandcast #256
1971 CB750K1
1972 CB750K1
1975 CB400F
1975 GL1000 Goldwing
1954 Harley Davidson Panhead
1957 Harley Davidson Panhead

Toronto Canada

Offline HondaMan

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Found my printed copy of HSB #42  Hopefully the pics of it are sufficient.

don't worry about the p/n hand written on it.  I wrote that for something else.



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. ;)
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline HondaMan

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I started a long-term "soak test" of the Honda tensioner vs. the Taiwanese tensioner, on 4/4/16. Post is in the Build Threads section. I half-immersed the rollers in used (by my bike) engine oil in a clear container, so they can be inspected from time-to-time to see if any damage happens. I don't have one of the "Made in Japan" rollers, though...
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline Harsh

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Found my printed copy of HSB #42  Hopefully the pics of it are sufficient.

don't worry about the p/n hand written on it.  I wrote that for something else.



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?

Offline HondaMan

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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. ;)
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline theslayedsaint

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Just a question hondaman, shouldn't the OME Honda tensioner from these bikes be from Japan?
1974 CB750 custom build cafe racer
-849cc big bore
-Webcam 63a
-APE rods
-4-1 stainless exhaust
-GSXR front end

Offline Davidov

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I got my 750F stitched back together.

After a close look at the tensioner, the cause of failure was unexpected.
At first it seemed like I had a case similar to PeWe, where the rubber disintegrated.
BUT it appears that the upper roller actually seized. So the chain was running along one side of the rubber, and eventually cracked it.
Yes, the rubber material was garbage. It was hardening, and there were cracks along the edge of the wheels.

After 1,000 miles on the original rebuild (09/2014), I did a tune up including a timing chain tension set. When I performed that, I remember that plunger snapped into place. Because it was probably pushing the metal portion of the roller directly on to the timing chain.
 I thoroughly inspected the chain, and found no signs of wear.

-David

Offline HondaMan

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Just a question hondaman, shouldn't the OME Honda tensioner from these bikes be from Japan?

I don't know for sure: the OEM ones are just marked "HONDA", no origin is listed. Since we see aftermarket types from both Taiwan and Japan, it's gonna be harder to sort out if the Japan-made aftermarket ones are OK or not? I don't have one of those among my collection right now, and don't remember which vendor I got it from, as I use CB750Supply, PartsNmore, VintageCB750, and a couple others when I can't get Honda's own stuff, sometimes.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline theslayedsaint

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That's strange because the ones I have say Honda and have ome numbers and are sold in separate packaging but also says made in Japan
1974 CB750 custom build cafe racer
-849cc big bore
-Webcam 63a
-APE rods
-4-1 stainless exhaust
-GSXR front end

Offline HondaMan

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I just ordered some more Honda ones last week, will see if their packages look any different?
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline PeWe

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I got my 750F stitched back together.

After a close look at the tensioner, the cause of failure was unexpected.
At first it seemed like I had a case similar to PeWe, where the rubber disintegrated.
BUT it appears that the upper roller actually seized. So the chain was running along one side of the rubber, and eventually cracked it.
Yes, the rubber material was garbage. It was hardening, and there were cracks along the edge of the wheels.

After 1,000 miles on the original rebuild (09/2014), I did a tune up including a timing chain tension set. When I performed that, I remember that plunger snapped into place. Because it was probably pushing the metal portion of the roller directly on to the timing chain.
 I thoroughly inspected the chain, and found no signs of wear.



Look like my failed tensioner. I cannot see any wear on my cam chain either. I have to replace it since it has been very tight the last 1000kms. The rubber halves of the upper wheel blocked the tensioner and chain was very stretched.

I have compared the chain with a new of same model, Tsubaki Camellia HD chain.
Same bend when holding chains horisontal, side by side like a striking cobra. Same lenght too when let them hang. Old chain might be good or have internal damages ready to snap.
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline Jerry Rxman Griffin aka MuthaF'er

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You guys keep ordering Honda ones and they'll run out and quit making them too.
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline PeWe

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You guys keep ordering Honda ones and they'll run out and quit making them too.

It is time for Honda to resume their part supply for their old good bikes! Their old suppliers might take own decisions after some years?
Bad aftermarket parts like this give me bad vibes...
I hope the aftermarket drive hub rubbers will withstand oil and pressure. I'll see if the engine must be opened again within a few years from now. Different with parts that does not need a complete tear down with the hard work and cost for gaskets and seals.
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline flybox1

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So the issue has just been with the tensioners from vintageCB750? The big (lower) tensioner roller in my bike is from CB750supply and was labelled as having been made in Japan. Upper tensioner assembly is OEM so I may have dodged a bullet there. Been a couple years and about 10,000 miles since they were installed and haven't had any noticeable issues. But now I'm paranoid...
Im in the same boat, but fewer miles.
Ill keep an eye out on the roller with my borescope every few hundred miles.
I did email CB750Supply to let them in on the issue with the other roller kits. . .

Thank you for your email.  We have heard about the issue with the Tensioner & Roller problem.  We are looking into it further.

Thank you,

CB750 Supply


I have yet to get a response on their findings, but I will follow up if I do.
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
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"Knowledge without mileage equals bullsh!t" - Henry Rollins

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Offline katman

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With just 300 miles on my rebuild am I going to have to re hone the cylinders or anything, or just gaskets and new tensioner.

Offline theslayedsaint

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Not sure why you would have to re hone anything. I'm reusing som of my mls gaskets but there's debate about that also. But with only 300 miles you are in the same boat as me! I'm pulling top end replacing some gaskets and throwing that damn tensioner out the window and got all new OME Honda parts.
1974 CB750 custom build cafe racer
-849cc big bore
-Webcam 63a
-APE rods
-4-1 stainless exhaust
-GSXR front end

Offline PeWe

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I got a letter from VintageCB750 informing me about the tensioner problem with warning and excuses about the problem for me. I have got email and refund + $50 check valid in their shop earlier.
They really do a lot about the problem!  I think that most companies out there should do less.
CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline tulsah

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I just acquired a 915 engine conversion that was started a couple of years back, but never completed.  Among the parts, I found this ...  What is the current advice/wisdom regarding its use?  Thanks in advance.


Offline grcamna2

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That's a slipper cam chain tensioner and looks to be High quality  8)
75' CB400F/'bunch o' parts' & 81' CB125S modded to a 'CB200S'
  I love the small ones too !
Do your BEST...nobody can take that away from you.

Offline tulsah

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Thanks for the reply!  There's no doubt that it's a quality piece.  I'm more wondering if these type of tensioners are still the way to go ... Cycle X no longer sells this one that I've been able to find.  I'd be concerned if there were known issue with it that has led away from its use.  Thanks again.