Topic: Cam Chain Tensioner Rubber Wheel Failure

[wjs]

Pulled my carbs because I have not been able to eliminate a miss which only happens when the bike is running at low speed and not under load especially when hot.  While the carbs were off decided to pull the cam chain tensioner and try to get a peak at the rubber tensioner wheels.

Found that the upper wheel was ground off on one side and must have just been sliding on the chain.  I had adjusted it a couple of times.  Remarkably it wasn't abnormally noisy and the engine still performed real strong.  I was just pushing the bike up to 90MPH a couple of days ago.  I can't believe that the engine didn't frag itself.  But now I think that the miss might be caused by valve timing with a sloppy cam chain.

Last month I pulled the oil pan and inspected the primary chain tensioner and the rubber wheel there was perfect.  But I did find a few small pieces of rubber in the pan.  I guess that I was in denial but suspected that it came from the cam chain tensioner or guide.

Now my question is what is the absolute minimum that I have to do to fix this?  If it's just the upper wheel can I replace it without removing the head or cylinder?  Doesn't look like it.  If I remove the head and cylinder can I just put it back without replacing the rings and honing the cylinder?  The engine runs strong at 29k and I don't see any reason to rebuild it.

[bryanj]

If pistons/rings are in spec no replacement or hone necessary, as to parts needed, with head and cylinders off replace ALL the rubber camchain tensioner parts and probably the cahin with a rivet link type

[wjs]

If pistons/rings are in spec no replacement or hone necessary, as to parts needed, with head and cylinders off replace ALL the rubber camchain tensioner parts and probably the cahin with a rivet link type

I imagine that the rings have wore in at a certain position.  Will they find that position again or do they have end pins keeping them in place?  I was thinking that the problem would be if the rings went back in at a different rotation than they wore in at.  Maybe I am overthinking.

Anyway got the engine completely disconnected and untethered last night but it's still sitting in the frame.  I was contemplating the best way to dismount it as it must be 350lbs.  Thought I would try putting a couple of short 2x4 pieces under it and jacking it and sliding it out sideways onto my motorcycle jack.

Thanks for your help.

--Bill

[Bob Wessner]

The engine doesn't weigh that much.. just seems like it. 

Might have a look at this thread re: removal techniques.

 http://forums.sohc4.net/index.php?topic=39702.0

[chickenman_26]

I imagine that the rings have wore in at a certain position.  Will they find that position again or do they have end pins keeping them in place?  I was thinking that the problem would be if the rings went back in at a different rotation than they wore in at.  Maybe I am overthinking.
--Bill

Just reposition the ring end gaps as shown in the service manual. They're not pinned and can move around in use. But do check the ring end gaps against specs - at least one of them. Parts for these bikes are going NLA at an alarming rate right now, so if the rings are at or past the limits, now's the time for new ones. Regarding the rubber parts, you got good advice to replace them. You're going to find that most all of them are hard and brittle, and that includes the valve stem seals. Some of the top end rubber and most of the gaskets are NLA, so you might want to go with an aftermarket gasket kit like Athena or Vesrah, but check all gasket alignments before assembly.

I realize you'd rather not spend any more or do any more work than absolutely necessary, but now's your chance to find and correct other problems. Do a compression test before opening the top end. I recently tore down a 750 that was running great but had severe oil leakage. And even though it ran with no apparent problems, the compression on one cylinder was low enough to make me investigate with a leak down test. Leaking exhaust valve. Turns out all exhaust valve faces were slightly pitted and had carbon deposits on the seating areas. The stem seals broke like pretzels when I removed them. And of course, all rubber cam tensioner parts were destroyed. So just a friendly warning - doing the bare minimum is likely to be a mistake.

Stu

[bryanj]

Rings actually rotate around the piston in use, which is hy they peg stroker rings

[MCRider]

Rings actually rotate around the piston in use, which is hy they peg stroker rings

"stroker" meaning 2 strokes? Or 4 stroke with a longer crank throw?

[chickenman_26]

Rings actually rotate around the piston in use, which is hy they peg stroker rings

"stroker" meaning 2 strokes? Or 4 stroke with a longer crank throw?

Two strokes. Their rings are pinned so the end gaps never get caught in the ports.

[wjs]

Thanks to all for the advice.  I slid the engine out onto my motorcycle jack after several trial and error attempts to position it so it would come out.   Then I just cranked it up to the top and the big motorcycle jack worked great as an engine stand.

When I positioned the engine a #1-4 TDC the cam marks lined up perfectly so I don't think the cam chain has much stretch in it.

I backed off all of the adjusters and slowly disassembled the rockers and bagging and numbered everything.  Used a small fiberglass tent pole stuck in the back of the jack to tie the cam chain up with - that worked great.  Pulled the cam out and the rocker assemblies with no problem.

Found all of the head bolt nuts and head bolts including the ones under the rubber plugs.  a couple of pops with a rubber mallet and the head came off.

The cylinder was a bit harder.  Not many places to pry without breaking a fin.  I pried a bit under the cam chain tensioner hole putting a little protection over the starter cover.  The cylinder came a bit loose on the back side and I managed to wiggle it with lots of effort until I finally got it off.

Bores looked real nice and pistons and rings all looked good except for some carbon on top.

The upper wheel on the cam chain tensioner was flat on one side and was obviously not turning but it was working quite well as a cam chain guide I guess.  Might have lasted quite a while before it actually cam apart.  Anyway the chain wasn't loose enough that it caused any damage. 


The lower wheel  was a bit chewed up on the ridge that rides in the chain center but otherwise was ok.  The slider chain guide on the front side looked fine.  I will post a picture today.

I'm ordering the full cam chain tensioner assembly with both wheels and the slider today as well as a top end gasket set.  I'm on the fence about whether I should hone and put new rings or just slide the cylinder back down over the old ones.  The engine with 29k ran strong, had good compression, didn't smoke or burn excessive oil and the bores look great.  Don't know what the best course is.

I will take the advice here and replace the valve guide seals. 

One observation is that these engines are quite complicated with the rocker assemblies and all of the various oil seals, plugs, and pins.  There are definitely lots of individual steps to remove the motor and disassemble it as well as put it back together.  It was too bad that it couldn't have been designed to replace these rubber parts without engine disassembly - same with the primary tensioner.
 

[wjs]

I don't think that one side of the upper wheel should be flat!  It was running good that way and might have run a lot longer with the chain sliding on one side of the wheel.

Anyway, after thinking it through I ordered a gasket set and standard ring set from Cyclex and all of the cam chain tensioner stuff from CB750Supply.com

Since the bores are super clean and there is no top lip except for carbon I'm just going to buy a dingle berry hone at about 280 or 320 grit and hone it a bit and then put everything back together.

[MCRider]

The wheel of my 305 SuperHawk had done the same thing. IT ran good but got noisy as it finally couldn't adjust any further. The wheel had seized on its bushing from sitting too long.

Is yours seized from turning?

[wjs]

It turned but was definitely tight in one spot.  The bike had sat for at least 8 years when I got it last year.  The motor turned freely but the carbs had not been drained and the bowls were full of green slime and the jets very dirty.

But, now having it apart, the pistons, bores, valves, valve gear, and everything else looks good and doesn't look like it suffered from corrosion.

I now have more $$$ in the thing than I paid for it but it has been an enjoyable hobby and I have learned a lot and continue to learn.  I thought this rebuild project was a bit too much for me but I am getting at it one step at a time.  Yesterday I decided to order new rings and pulled the pistons.  At first I wasn't going to do that.

Now I am trying to figure out the best way to decarbon the tops of the pistons and the combustion chambers.  Tried a wire brush and that didn't work too well.

[MCRider]

Soda blast is the most benign way to clean used parts for reuse. If you don't want to buy or make your own, I or others may be able to do it for you.

Water clean up,

[chickenman_26]

Now I am trying to figure out the best way to decarbon the tops of the pistons and the combustion chambers.  Tried a wire brush and that didn't work too well.

Go to Home Depot and buy a gallon of Jasco Stripper. Paint it on the parts good and thick, then let it sit overnight. Clean up the parts with water and a wire scratch brush. Caution - wear protective gloves when working with Jasco. It'll really mess with any exposed flesh it gets on. I'm surprised OSHA hasn't banned it like they have other good products...bastards.

Stu

[wjs]

I read somewhere on this forum that soaking in simple green would loosen it up.  I now have the piston sitting in a small bucket of it.  If that doesn't work I'm going to get some of the Jasco or look into soda blasting.

I'm still waiting for parts.  Getting my rings and gaskets from Cyclex.  My past experience with them has been good, so I'm not worried there.  But I'm not sure about the cam chain stuff coming from CB750Supply.com.  They are not good about communicating the status of your order or tracking numbers.

I ordered some stuff from VintageCB750.com over two weeks ago.  Don't have it and haven't had any communication from them.  I didn't realize they were in Canada until I looked at the contact info.  Anyway these 2 outfits seem to be the same company or affiliated as there web sites and manor of doing business are very similar.

[lucky]

The engine doesn't weigh that much.. just seems like it. 

Might have a look at this thread re: removal techniques.

 http://forums.sohc4.net/index.php?topic=39702.0

Just lay the bike on its side.

[wjs]

Wow!  The Simple Green worked.  I put the pistons in a small bucket with SG.  The next morning I just wiped the carbon off.

[tlbranth]

I don't think that one side of the upper wheel should be flat!  It was running good that way and might have run a lot longer with the chain sliding on one side of the wheel.

Anyway, after thinking it through I ordered a gasket set and standard ring set from Cyclex and all of the cam chain tensioner stuff from CB750Supply.com

Since the bores are super clean and there is no top lip except for carbon I'm just going to buy a dingle berry hone at about 280 or 320 grit and hone it a bit and then put everything back together.

I don't see any reason to hone the cylinders. You'd just be adding unnecessary wear to an engine that's already broken in.

[chickenman_26]

I don't see any reason to hone the cylinders. You'd just be adding unnecessary wear to an engine that's already broken in.

If he weren't replacing the rings, you'd be correct. But using new rings, it won't be broken in any more. He definitely wants to break the glaze and leave a crosshatch if he wants those rings to seat...within his lifetime. A BRM  Flex Hone won't remove more than
 .0001" during the dozen or so strokes necessary, and break in will be pretty quick. I just finished this job on my 750A, and that's the bore size increase my bore gauge showed - one ten-thousandth of an inch.

Stu

[tlbranth]

I don't see any reason to hone the cylinders. You'd just be adding unnecessary wear to an engine that's already broken in.

If he weren't replacing the rings, you'd be correct. But using new rings, it won't be broken in any more. He definitely wants to break the glaze and leave a crosshatch if he wants those rings to seat...within his lifetime. A BRM  Flex Hone won't remove more than
 .0001" during the dozen or so strokes necessary, and break in will be pretty quick. I just finished this job on my 750A, and that's the bore size increase my bore gauge showed - one ten-thousandth of an inch.

Stu

Indeed. I thought he was just reassembling with old rings and pistons. My bad.

[lucky]

Shortened

What about all the little bits of rubber that can get into the crankshaft journals?

To get the engine out just leave two long rear bolts in it and lay the bike on its side on old sleeping bags or blankets. Then remove the two remaining bolts.
Then lift the bike off of the engine. You did drain the oil right?

Here are two photos from the TECH tips section of CYCLE-X website.
"Removal of the crankshaft oil ball bearings will expose 30 plus years of sludge.
Cleaning these blind oil holes can be difficult................. so, tapping and install socket head plugs will allow you to clean properly.  "

[wjs]

Got all of my parts.  Did buy a 2 1/2 dingle berry hone 320 grit.  I ran it through 7 or 8 times in each hole.  Seemed like it had a decent cross hatch.  Then noticed my #2 hole had a scratch in it.  So I'm debating giving it a bit more.

CycleX head gasket is odd.  It has 3 layers.  I guess they know what they are doing.

I'm not going to touch the bottom end although it could probably use some work.  There was sludge in some of the oil holes in the pistons and I think a couple might have been plugged.  Used a small drill bit by hand to clean them.

I'm just replacing the valve guide seals but all of the seats and valve faces look very good.  Not going to lap them.

Over the Labor day weekend, I'm going to stick it all back together and hope for the best.  Hopefully I won't have to tear it apart again before next year.

Thanks for all of the help and advice.

[MCRider]

Got all of my parts.  Did buy a 2 1/2 dingle berry hone 320 grit.  I ran it through 7 or 8 times in each hole.  Seemed like it had a decent cross hatch.  Then noticed my #2 hole had a scratch in it.  So I'm debating giving it a bit more.

CycleX head gasket is odd.  It has 3 layers.  I guess they know what they are doing.

I'm not going to touch the bottom end although it could probably use some work.  There was sludge in some of the oil holes in the pistons and I think a couple might have been plugged.  Used a small drill bit by hand to clean them.

I'm just replacing the valve guide seals but all of the seats and valve faces look very good.  Not going to lap them.

Over the Labor day weekend, I'm going to stick it all back together and hope for the best.  Hopefully I won't have to tear it apart again before next year.

Thanks for all of the help and advice.

Sounds like you got a MLS gasket? MLS = multi layer steel.