Cam Chain tensioner & guides


Stevo
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Cam Chain tensioner & guides

Post by Stevo »

Hi all, has anyone come up with any ideas to repair the Cam chain tensioner and guides ie the running surface is not worn but is cracked. Starting to wish I had never bought this bike, after modifying swing arm to fit non std bearings now find I can't get any tensioner or guides anywhere, sorry should rephrase that a supplier in the US will sell me the small tensioner for $850.00 at that price I could buy another engine. Has anyone put the cracked tensioner and guides back in, do they last? - Are these parts interchangeable with other models ie CB900F and other DOHC models from same era?
Need help.

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Re: Cam Chain tensioner & guides

Post by daves79x »

This is getting to be a problem. The remaining new tensioners fetch very high prices. Good used ones are less, but still steep. Bert at Six Center rebuilds some of them for a decent price and guy seem happy with them. There are no direct matches with tensioners of the F bikes, but someone, I think on Facebook, had used a 900F tensioner he modified slightly with success. They must still be available. Can't confirm or deny that that works - it was Facebook after all.

If the cracks aren't too bad, you can re-use the tensioners.

Some enterprising soul will likely come up with replacements, at a price of course, as demand grows. The price of admission keep going up!

Dave

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Re: Cam Chain tensioner & guides

Post by Louis »

Stevo wrote:Hi all, has anyone come up with any ideas to repair the Cam chain tensioner and guides ie the running surface is not worn but is cracked. Starting to wish I had never bought this bike, after modifying swing arm to fit non std bearings now find I can't get any tensioner or guides anywhere, sorry should rephrase that a supplier in the US will sell me the small tensioner for $850.00 at that price I could buy another engine. Has anyone put the cracked tensioner and guides back in, do they last? - Are these parts interchangeable with other models ie CB900F and other DOHC models from same era?
Need help.
I am the person (www.usedcbxparts.com) that has priced you that on the B tensioner as well as other tensioners and guides. I am sorry that they are that price, but when i buy them now they are not cheap. I do have good used ones as well as rebuilt new A tensioners. All i can say i wish someone would make new ones and before they sell them use them for a few thousand miles and take motor apart and look at them.A few in the past had made them and they have come apart and that is not good. So as long as i keep on buying them at high prices they will have to be sold with a profit, but the good thing is that i have any of them you want NOS as well as good used if you want it.
By the way you i do not think you can buy a good motor for $850.00 and if you could go get it. You can use cracked ones as long as the cracks are not on the top.

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Re: Cam Chain tensioner & guides

Post by Stevo »

Hi Louis did not mean to offend just didn't expect this problem, which sought of blows the budget out a bit. I completely understand prices for rare items will be high, but I can't justify that price, well not yet. I will contact Bert at Sixcenter to see if he can help.
When you say OK to use as long as the cracks are not on the top, my tensioners are cracked where the chain runs if the tensioner is stretched out like it would be in the engine the cracks close but when the spring pulls the ends together out of the engine the cracks open up every 1/2 inch or so, is this what you mean by cracks in the top. I have not studied them really closely but assume there is a metal backing has anyone attempted to attach material to the backing?

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Re: Cam Chain tensioner & guides

Post by Louis »

Stevo wrote:Hi Louis did not mean to offend just didn't expect this problem, which sought of blows the budget out a bit. I completely understand prices for rare items will be high, but I can't justify that price, well not yet. I will contact Bert at Sixcenter to see if he can help.
When you say OK to use as long as the cracks are not on the top, my tensioners are cracked where the chain runs if the tensioner is stretched out like it would be in the engine the cracks close but when the spring pulls the ends together out of the engine the cracks open up every 1/2 inch or so, is this what you mean by cracks in the top. I have not studied them really closely but assume there is a metal backing has anyone attempted to attach material to the backing?
No offence taken at all. I have seen guys use them with cracks on top, but i think the least amount of cracks it will be longer before you have a break down of tensioners and have to replace again. Dave might chime in and add to this as well. He works on these motor and i am sure he can advise you in many ways. Bert might have options as well. If i can help you with anything just let me know.
Louis

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Re: Cam Chain tensioner & guides

Post by daves79x »

Here are my thoughts on this and a few related comments. Small hairline cracks that don't open up much upon flexing the tensioners I think are fine to use. I've been lucky in that the engines I've worked on have had good tensioners and I've managed to squirrel away several good used sets. Which brings me to my other point - most of the engines I've worked on have been known to spend their lives in the cooler Northern climate. It has become apparent to me that extreme heat is the real enemy of these things. In the course of doing dozens and dozens of sets of carbs from all over, a pattern developed - Carbs from say, Florida or Arizona or Texas consistently had far more deterioration of the rubber parts than carbs from cooler climates. This is very especially seen in the throttle link joint covers. Many sets from up North I can salvage, but almost none of the rubbers from other areas are useable. They are just crispy. Same with intake rubbers.

So if you extrapolate this theory to the other internal engine rubber parts, destroyed cam chain tensioners are a result. Long-time readers here will remember me railing quite often against letting these bikes sit and idle in hot traffic. I know that's what happens to many of these bikes and this kind of thing is a result. My personal '79, except for one trip to Florida and one trip to the Southwest and West coast, has spent it's entire life in moderate climates and the intake rubbers and camchain tensioners are like new, with nearly 50,000 miles on it. Another CBX I service from West Virginia has 90,000 miles and those parts are still serviceable. I restored an '80 that was this same guys' that had 80,000 miles and again, those parts were serviceable.

So my conclusion is that the heat destroys these things. If the CBX you recently acquired needs new cam chain guides, the intake rubbers are crispy, etc, I'll just about guarantee the bike has gotten very hot, very often.

Dave

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Re: Cam Chain tensioner & guides

Post by cbxchris »

daves79x wrote:Here are my thoughts on this and a few related comments. Small hairline cracks that don't open up much upon flexing the tensioners I think are fine to use. I've been lucky in that the engines I've worked on have had good tensioners and I've managed to squirrel away several good used sets. Which brings me to my other point - most of the engines I've worked on have been known to spend their lives in the cooler Northern climate. It has become apparent to me that extreme heat is the real enemy of these things. In the course of doing dozens and dozens of sets of carbs from all over, a pattern developed - Carbs from say, Florida or Arizona or Texas consistently had far more deterioration of the rubber parts than carbs from cooler climates. This is very especially seen in the throttle link joint covers. Many sets from up North I can salvage, but almost none of the rubbers from other areas are useable. They are just crispy. Same with intake rubbers.

So if you extrapolate this theory to the other internal engine rubber parts, destroyed cam chain tensioners are a result. Long-time readers here will remember me railing quite often against letting these bikes sit and idle in hot traffic. I know that's what happens to many of these bikes and this kind of thing is a result. My personal '79, except for one trip to Florida and one trip to the Southwest and West coast, has spent it's entire life in moderate climates and the intake rubbers and camchain tensioners are like new, with nearly 50,000 miles on it. Another CBX I service from West Virginia has 90,000 miles and those parts are still serviceable. I restored an '80 that was this same guys' that had 80,000 miles and again, those parts were serviceable.

So my conclusion is that the heat destroys these things. If the CBX you recently acquired needs new cam chain guides, the intake rubbers are crispy, etc, I'll just about guarantee the bike has gotten very hot, very often.

Dave
There could be some logic in that Dave, as my bike is from South Africa, which is warm country and one of my tensioner's has fairly bad cracks, although it has covered 80,000 km's !

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Re: Cam Chain tensioner & guides

Post by wyly »

the mechanic rebuilding my engine says he's rebuilt tensioners for other bikes...he hadn't made one for a CBX as yet and it would depend on how the CBX's tensioners were constructed but if he could he thought it might cost about $100ish ...I'll ask him next time I'm in his shop...

when I bought my replacement head for $200 it came with the small tensioner free! which made my day... :D
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Re: Cam Chain tensioner & guides

Post by Stevo »

Thanks Wyly, I have searched for a material to attach to the original metal backing but cannot find anything that can withstand the heat, looked at Nylon products, no adhesive that can take the heat so material would have to be bolted on with countersunk bolt heads which would not be a problem, but it all comes down to the material itself.

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Re: Cam Chain tensioner & guides

Post by CopperCollar »

I used to know a guy here in Albuquerque that made chain tensioners for the DOHC F bikes. I bought a set for a 79 DOHC CB 750F and they were great but they had to be manually adjusted as they were a solid piece of material machined with an arc that set in place of the original Honda adjusters.

Looked him up last year only to find he had passed away and no one knew of the material he used. I do remember it looking like a moly plastic of some sort.

Tried in vane to find someone to make up adjusters but every machinist I approached passed on the request.

Doing some research and it would seem the best material for this would be Nylon 4.6, this has a melting temp of 295 degrees. The questions are
a) How hot does the oil get in these air cooled CBX engines, if less than 295 degrees then the Nylon 4.6 should work.
b) Using Nylon 4.6 ; can a machnist be found that will invest the time to machine the Nylon 4.6 into a working tensioner.
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Re: Cam Chain tensioner & guides

Post by herdygerdy »

For sure, sourcing both the A and B tensioners for the CBX is fast becoming more and more problematic.

Over on the cb1100f.net site, 'Captain' (and his race bike is currently featured on the home page) manufactures replacement A and B tensioners for the twin cam fours. For the A chain, he supplies both a tensioner and front curved guide and also a tensioner for the B chain.

He also has both A and B chains for the fours and our sixes that are VERY high quality - far better than what Honda will sell you today for our engines.

Hundreds of tensioner and guide sets now sold around the world, many used for endurance and other racing.

Making something similar for the CBX engine is on Captain's radar, but unfortunately down his priority list, what with a trip across here to Sydney for Eastern Creek Festival of Speed in late March, then off to Spa Francorchamps again in late June/July.

However, if and when they come, I am sure they will be well worth the wait.

He also goes by 605brent on the other CBX site, so maybe send him a PM, or he may even chime in here...

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Re: Cam Chain tensioner & guides

Post by Captain »

CopperCollar wrote:I used to know a guy here in Albuquerque that made chain tensioners for the DOHC F bikes. I bought a set for a 79 DOHC CB 750F and they were great but they had to be manually adjusted as they were a solid piece of material machined with an arc that set in place of the original Honda adjusters.

Looked him up last year only to find he had passed away and no one knew of the material he used. I do remember it looking like a moly plastic of some sort.

Tried in vane to find someone to make up adjusters but every machinist I approached passed on the request.

Doing some research and it would seem the best material for this would be Nylon 4.6, this has a melting temp of 295 degrees. The questions are
a) How hot does the oil get in these air cooled CBX engines, if less than 295 degrees then the Nylon 4.6 should work.
b) Using Nylon 4.6 ; can a machnist be found that will invest the time to machine the Nylon 4.6 into a working tensioner.
Vince & Hyde Racing are the developers and only known manufacturer of the Curved Guide and AHM Tensioner for the DOHC F bikes (and we are not deceased ). Over 700 sets manufactured and supplied to users around the world to date and it sounds to me that someone was trying to copy ours and as I have never disclosed the material used I doubt that anyone has been successful. What we produce was born from the discoveries of the cam chain issues that have plagued the 4's from the time of first manufacture and once we correctly identified the harmonic event we engineered the correction and which since has gone on to be the industry standard for the cam chain upgrade. Most competition engines worldwide have these parts fitted and Vince & Hyde Racing are intending to manufacture a up-spec / up grade cam chain tensioner for the CBX along the same lines as that produced for the 750-1100 DOHC 4's.


Captain
Last edited by Captain on Tue Feb 27, 2018 3:25 pm, edited 1 time in total.

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Re: Cam Chain tensioner & guides

Post by patzx12 »

The highest temp plastic are:
Duratron PBI & Peek.
I use these from time to time in Injection moulds, I have a supplier here in Ireland.
I am a precision engineer but have never done anything with tensioners.
Sitting here at the PC I wouldn't fancy bonding them. Screwing them down would be a good option but as stated it would be down to putting them into an engine and running them (racing preferably).

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Re: Cam Chain tensioner & guides

Post by wyly »

patzx12 wrote:The highest temp plastic are:
Duratron PBI & Peek.
I use these from time to time in Injection moulds, I have a supplier here in Ireland.
I am a precision engineer but have never done anything with tensioners.
Sitting here at the PC I wouldn't fancy bonding them. Screwing them down would be a good option but as stated it would be down to putting them into an engine and running them (racing preferably).
http:/would you trust a screw not to come loose in that situation? ...I'd think a rivet or two would be a more secure option...but then I don't know much :? ...
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Re: Cam Chain tensioner & guides

Post by patzx12 »

True, but there are ways of securing screws. After all your whole motorcycle is held together with screws.
The hi spec plastics do not bend, they would have to be machined with the curvature.
Bloody expensive BTW

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