cb650 cam chain

Mr-Wolf

New Member
Hey guys,

I am currently in the process of doing a ground up rebuild on a 1979 cb650 basket case.
I have already finished completely redoing the wiring (per my only other post of an updated wiring diagram), and now ave the motor taken down to the lower end.

The back story of the bike is, I bought it from a guy who was going to try and rebuild it. He got it as a whole bike and took it completely apart and painted the frame.....and that was that, he decided he no longer wanted to rebuild it and it sat in his garage for a few years. Then I picked it up in hopes that I could see what I was made of and rebuild my first bike from the ground up. I have no information from the guy about the PO, but upon rebuilding the motor I have found that (I assume) the cam chain went bad and chewed up the case a bit, but was replaced. I say replaced because the guide and tensioner show absolutely no wear marks from a chain rubbing on them, and as far as a visual inspection for the chain I see no marks of it having rubbed on the case. However, the dampener has some cracks forming on the end.
My questions are this:
What is an easy way to test to make sure the chain is in good specs.
and do i need to replace this dampener?
Money is extremely tight here, I had some cash to order everything I figured I would need at the beginning of the year, but now I am strapped. The pictures below are of the tension, guide so you can see if I am correct in that they are new, and case rubbing because who doesn't like carnage pictures.
If I could get some insight on in that dampener needs to be replaced, and wear I can get one for cheap if it does need to be replaced I would greatly appreciate it.


Thank you for any help!
 

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Mr-Wolf

New Member
Bumping.

If someone can confirm my thought that the chain has tensioner/guide has been replaced. If you look at the second to last picture there is a weld spot in the case. That confirms to me that the motor has been apart to fix the chain in the past. Or am I crazy??? I could really use some help in this as I am a rookie and at a total loss.
 

hillsy

Active Member
Mr-Wolf said:
What is an easy way to test to make sure the chain is in good specs.

If you have a workshop manual it should tell you how to measure the chain to check for wear. Normally they give you a measurement to check over a dozen links or so.





Those guides look good to me.
 

Mr-Wolf

New Member
hillsy said:
If you have a workshop manual it should tell you how to measure the chain to check for wear. Normally they give you a measurement to check over a dozen links or so.





Those guides look good to me.


Thank you for the reply! I will see if I can find that info in my manual.
I agree, last night I scoured ebay looking at the few dampeners I could find, they all look par or worse then this one so I will be running it. Looks like now I can get back to the rebuild!
 

teazer

Well-Known Member
DTT BOTM WINNER
Something doesn't look right there. Can you post more pictures of that nasty gouging in the barrels and crankcases please. It looks like the chain gouged the heck out of the sides of the tunnel and that's not a common wear pattern. Front and back wear from a loose chain is not unusual but that gouging is deep and nasty looking.

Where is the "weld spot" that you commented on?
 

Mr-Wolf

New Member
Teazer,

I agree those are not normal wear marks. I believe there was a cam chain / guide failure of some kind and they replaced the parts and rebuilt the motor after, which would explane the slipper on the tensioner having no wear marks.
The second to last picture, bottom left gouge is were you can see the weld, it looks pretty decent for the angle required and I do not see any external indications that the chain went through the case probably a shop job to repaire and replace?

This is the only other picture I have.
 

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teazer

Well-Known Member
DTT BOTM WINNER
I see what you are talking about. It would be a good idea to split the crankcases, but do not drop the main bearing shells out and mix them up.
 

Mr-Wolf

New Member
What would I be looking for if I split the crank case?
I plan on dropping the oil pan before reassembly to make sure there isn't any metal chuncks down there.
 

teazer

Well-Known Member
DTT BOTM WINNER
You are looking for any other damage. Something odd happened to have that chain flapping about like a politician's gums. The grooves in the barrel tunnel are ugly but not fatal. The crankcases look worse and that suggests that the chain was loose and came off the sprocket and machined those grooves. If you can see with the sump off or with a small mirror or borescope, check to see there is not serious damage where the chain thrashed around.
 

crazypj

Split personality, I fake being smart
Fit a new chain, they are not supposed to wear but in my experience they move around a lot and cut into stuff. (nowhere near as bad as the CB900 though)
The tensioner should be OK as the crack isn't in wear area. It was probably caused by chain not being adjusted at service interval so slapping around
With hy-vo chains, as they wear they ride much higher on sprockets, wear grooves are the result
Those cylinders look pretty nasty, doing a 700cc kit?
hillsy said:
If you have a workshop manual it should tell you how to measure the chain to check for wear. Normally they give you a measurement to check over a dozen links or so.




Those guides look good to me.
If I remember right, you have to have a specific weight to 'stretch' chain then measure pin distance. Personally, from experience of the HY-Vo, just fitt a new one
 

Mr-Wolf

New Member
crazypj said:
Fit a new chain, they are not supposed to wear but in my experience they move around a lot and cut into stuff. (nowhere near as bad as the CB900 though)
The tensioner should be OK as the crack isn't in wear area. It was probably caused by chain not being adjusted at service interval so slapping around
With hy-vo chains, as they wear they ride much higher on sprockets, wear grooves are the result
Those cylinders look pretty nasty, doing a 700cc kit?
If I remember right, you have to have a specific weight to 'stretch' chain then measure pin distance. Personally, from experience of the HY-Vo, just fitt a new one

Well, I hadn't really looked at the Pistons that hard till you said that. I tried honing then up to see what they looked like and there is no chance of keeping it stock. so I think I will do a 61mm piston from a cb750k if I can find them.
 

teazer

Well-Known Member
DTT BOTM WINNER
There are really good looking pistons http://www.dynomanperformance.com/engine/pistons/piston-install/62mm-SOHC.pdf

Or go with CruzinImage at a fraction of the cost and I wopuld expect them to be be perfectly OK for your application. http://www.ebay.com/itm/79-82-HONDA-CB650-1-00mm-OVERSIZE-PISTONS-SET-4-PISTONS-INCLUDE-CI-CB650APS-2-/161856493778?&_trksid=p2056016.m2518.l4276

We use their stuff, including pistons in any number of street GT550 and 750 motors. In fact the pistons in my race bike came from there. I don't expect them to last forever in that abusive situation but for a street part at a great price, they are great value for money.
 

Mr-Wolf

New Member
teazer said:
There are really good looking pistons http://www.dynomanperformance.com/engine/pistons/piston-install/62mm-SOHC.pdf

Or go with CruzinImage at a fraction of the cost and I wopuld expect them to be be perfectly OK for your application. http://www.ebay.com/itm/79-82-HONDA-CB650-1-00mm-OVERSIZE-PISTONS-SET-4-PISTONS-INCLUDE-CI-CB650APS-2-/161856493778?&_trksid=p2056016.m2518.l4276

We use their stuff, including pistons in any number of street GT550 and 750 motors. In fact the pistons in my race bike came from there. I don't expect them to last forever in that abusive situation but for a street part at a great price, they are great value for money.
Is this just a bore out and replace Pistons with the cruizin image set? Do I need an oil cooler if I do this? And how far would I have to have the cylinder bored to? 61mm?
 

teazer

Well-Known Member
DTT BOTM WINNER
Yes - it's a straight 1mm o/s bore and hone job.

No - oil cooler not strictly necessary, but might be a nice (future) upgrade if you can find one

1mm larger than stock. Stock was 59.8 I believe, so that would make it 60.8mm finished bore size. Your machinist will measure all 4 pistons and will bore and hone to the correct clearance for each pot. Pistons will come back marked 1-2-3-4 and will match the bores. Try not to mix them up.
 

Mr-Wolf

New Member
Thank you so much for your help!!!! I luckily have a profession machinist brother who will do the work for a case o'beer....or a few bottles of homebrew, so it looks like it will be an easy and cheaper then expected swap for me.
And I am sure I can resell my pistons and brand new rings on here with other misc parts I have laying around (including side covers).
I could kiss you, but that would be weird........Thank you so much for your help!!!!
 

teazer

Well-Known Member
DTT BOTM WINNER
Your brother has to hone the bores to finished size to get the correct clearance and surface finish. It's not quite the same as a normal machining job, but I am sure he can get it right.
 

Mr-Wolf

New Member
Am I cool to run my current set up of Mac 4-1 headers and #120 / #42 jets with pods for the overbore? Probably a dumb question but it's late and my head is swimming.
 

teazer

Well-Known Member
DTT BOTM WINNER
That rather depends on whether that combo worked before.. As long as you have a decent muffler and filters, you can jet it when it's running. Do you know what stock jets are for that bike as a point of reference?
 

Mr-Wolf

New Member
Well, I got the bike as a basket case so I have no idea how it ran before. However the jets and headers idea I got from a few other forums where people have used that set up with stock cb650s with great success.
stock is 92/35

Now I just need to find ignition coils...that aren't going to break me anymore then this overbore already has.
 

crazypj

Split personality, I fake being smart
I have a couple of sets of NOS 0.75mm oversize CB750 SOHC pistons, BUT, no rings, pins or circlips
 

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