Author Topic: CB750: Aware of cheap parts -tensioner rubber cracked in 2- Carb boots cracking (Read 48725 times)

AshimotoK0 · « **Reply #175 on:** April 05, 2016, 05:03:57 PM »

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

Jerry Rxman Griffin aka MuthaF'er · « **Reply #176 on:** April 05, 2016, 06:12:58 PM »

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?

millla03 · « **Reply #177 on:** April 05, 2016, 07:08:50 PM »

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...

Harsh · « **Reply #178 on:** April 06, 2016, 04:37:59 AM »

Quote from: Jerry Rxman Griffin aka MuthaF'er on April 05, 2016, 06:12:58 PM

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

Harsh · « **Reply #179 on:** April 06, 2016, 09:25:17 AM »

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.

Prospect · « **Reply #180 on:** April 06, 2016, 09:44:29 AM »

Quote from: Harsh on April 05, 2016, 10:24:35 AM

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.

HondaMan · « **Reply #181 on:** April 06, 2016, 12:56:37 PM »

Quote from: Harsh on April 06, 2016, 09:25:17 AM

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.

HondaMan · « **Reply #182 on:** April 06, 2016, 12:59:36 PM »

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...

Harsh · « **Reply #183 on:** April 06, 2016, 04:14:22 PM »

Quote from: HondaMan on April 06, 2016, 12:56:37 PM

Quote from: Harsh on April 06, 2016, 09:25:17 AM
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?

HondaMan · « **Reply #184 on:** April 06, 2016, 05:55:19 PM »

Quote from: Harsh on April 06, 2016, 04:14:22 PM

Quote from: HondaMan on April 06, 2016, 12:56:37 PM

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.

theslayedsaint · « **Reply #185 on:** April 07, 2016, 08:29:38 AM »

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

Davidov · « **Reply #186 on:** April 08, 2016, 12:28:54 PM »

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.

HondaMan · « **Reply #187 on:** April 09, 2016, 07:02:28 PM »

Quote from: theslayedsaint on April 07, 2016, 08:29:38 AM

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.

theslayedsaint · « **Reply #188 on:** April 09, 2016, 08:59:50 PM »

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

HondaMan · « **Reply #189 on:** April 10, 2016, 10:16:35 PM »

I just ordered some more Honda ones last week, will see if their packages look any different?

PeWe · « **Reply #190 on:** April 11, 2016, 12:41:02 AM »

Quote from: Davidov on April 08, 2016, 12:28:54 PM

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.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #191 on:** April 11, 2016, 07:47:30 AM »

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

PeWe · « **Reply #192 on:** April 11, 2016, 09:00:32 AM »

Quote from: Jerry Rxman Griffin aka MuthaF'er on April 11, 2016, 07:47:30 AM

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.

flybox1 · « **Reply #193 on:** April 11, 2016, 09:35:14 AM »

Quote from: millla03 on April 05, 2016, 07:08:50 PM

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.

katman · « **Reply #194 on:** April 11, 2016, 12:59:44 PM »

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.

theslayedsaint · « **Reply #195 on:** April 11, 2016, 01:28:54 PM »

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.

PeWe · « **Reply #196 on:** April 11, 2016, 11:33:44 PM »

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.

tulsah · « **Reply #197 on:** May 18, 2016, 06:15:10 PM »

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.

grcamna2 · « **Reply #198 on:** May 19, 2016, 01:43:28 AM »

That's a slipper cam chain tensioner and looks to be High quality

tulsah · « **Reply #199 on:** May 19, 2016, 01:57:29 PM »

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.

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Author Topic: CB750: Aware of cheap parts -tensioner rubber cracked in 2- Carb boots cracking (Read 48725 times)