Author Topic: Broken Cam Chain? (Read 5132 times)

joeyrobots · « **on:** June 21, 2015, 08:52:51 PM »

Hello all, i've been reading the forum for years but its my first time posting. I have a 1975 Honda CB550 that I bought for $550 12 years ago. This forum has helped guide me from a stupid college kid with a lot of determination but few skills into a fairly competent mechanic. Unfortunately, I have run into a problem with is truly vexing.

The bike has about 35K miles on it, but all systems have been serviced throughout over the years by me, excepting the engine. The bike runs like a dream, and always turns over with two kicks even after months in storage. Recently though I have had an oil leak develop on the head gasket, and was planning a top end rebuild this winter. But about a week ago the cam chain started rattling around a little bit, making noise, which previously I've been able to correct via the tensioner. So i didn't think much of it, until the other night when the bike made an odd noise and then just died.

I have spark, and the carbs were just cleaned and re-jetted this year, so mixture is no issue. But now I am getting zero compression on cylinders 1, 3, and 4, with low compression on cylinder 2, about 65psi. I am not getting any suction through the airbox when i kick it, rather I had some fuel dripping from the boot between the box and the carbs on cylinder 4. Then I opened the valve covers and there is a lot of oil up there, which came pouring out the low side when the bike was on the kickstand. When I kick it, the rockers aren't moving at all, nothing. So i popped the breather cover to have a look. There you can see the cam chain through some small windows/slots in the front. I poked my screwdriver in and the cam chain lifts off cam sprocket very easily, exposing the teeth with no resistance.

I searched the forum and can't find very much experience or info with broken cam chains or replacing them. My guess here is that my top end rebuild plans are being moved up a few months, and that I will have to drop the oil pan to thread a new cam chain through. I was hoping somebody can give me some advice of what my actual problem here may be, what I'm getting into, what I should be mindful of, what damage i should look for, and why the cam chain may have failed, if that is indeed the case. I will know more as I start to pull the top end off, and will update with photos. Looking for any feedback I can get before I begin this. How long should I budget for the top end service? Its now officially summer and my ride to the beach won't turn over, so I do want to get this sorted asap.

thanks for your advice,
d

evanphi · « **Reply #1 on:** June 22, 2015, 08:03:44 AM »

A cam chain shouldn't just fall apart when not riding... and I would think if it came off while riding it would have been quite catastrophic. While at idle, though... maybe just would have caught up and died.

You're giong to have to take it all apart, though to find out.

Get to it!

Drop your oil pan, for starters. Look for big pieces... chain, chunks of alu, etc.

joeyrobots · « **Reply #2 on:** July 05, 2015, 07:43:14 PM »

So i took the top end off an dropped the oil pan this weekend and there is definitely some carnage in there. As I suspected, the cam chain snapped. I'm not sure what started it or the order of failure was, but it looks like the front cam chain guide was just shredded, its in a few pieces. The slipper from the cam chain tensioner is broken as well.

My bigger concern is the slots in the cylinder block that the cam chain guide rests in. The slots look like they've been worn out, gouged a bit, and in addition there is some marring above them on the cylinder head. Has anybody seen this before, can advise? There are also parallel grooves on both the block and the head, pathways worn in from the cam chain. I'm hoping I can get away with just a new cam chain guide and slipper on the tensioner, as well as a new chain. Thoughts?

Also apparently I have a bent exhaust valve as well, so i will be taking care of that.

thanks!

links56 · « **Reply #3 on:** July 05, 2015, 08:04:22 PM »

Can you post some more pictures of the motor? The top of the piston that has bent valve? Also the teeth on the sprockets? The cylinder walls? and all 4 spark plugs? Sorry for asking for all this. I'm curious if the chain caused the bent valve or the bent valve caused the chain to break. It Looks like the motor has an awful lot of carbon build up in the cylinders. Looks like possibly some scoring on the cylinder walls. Also does the bent valve move freely? I wouldn't be too concerned with the spots where the chain has been rubbing on the block.

eigenvector · « **Reply #4 on:** July 05, 2015, 08:45:22 PM »

I've had my cam chain jump the sprocket before. It sucks, it does a tremendous amount of damage in the process, but ultimately it is fixable. Of course fixable usually means full rebuild, but on an air cooled bike like this that isn't as difficult as it may sound.

The most difficult part is, oddly enough, finding replacement guides for the chain. I manufactured new guides myself, but really I would have preferred original parts.

Bent valves are easy to fix, so long as the guides are still good.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #5 on:** July 05, 2015, 08:55:11 PM »

Do you know what was done to it when it was taken apart the last time (as told by the arrow on the piston)?

joeyrobots · « **Reply #6 on:** July 05, 2015, 08:56:28 PM »

I can post some more photos tomorrow. The bike is at my girlfriends apartment because she has a basement I can work in.

The teeth on the cam sprocket look a bit worn but are all intact. I couldn't get the valve to move easily when i pushed on it, but i didn't give it too much force. I will give it another go tomorrow, and probably just remove it then. The bike itself was running great, but started with some cam chain rattle noise a few days prior. I've had that noise before with no real problem, and have always been able to run fine with a little buzzing until i had a moment to adjust the tensioner. I was planning on doing the adjustment shortly, and then it broke down. When it broke down, there was a loud clank, and that was it. very sudden.

There is a lot of carbon in there, I was a bit surprised. About 4 years ago, after the bike sat in storage for three years because of some parking ticket issues, i replaced the paper in the air filter with UniFoam. The paper filter was old and grimy and clogged, so it wasn't getting enough air for basically all of college, when i didn't know any better. Maybe all those deposits are from that? Though I did notice the plugs were sooty last time i pulled them, so its still running rich

Pictures tomorrow. Thanks.

joeyrobots · « **Reply #7 on:** July 05, 2015, 09:01:10 PM »

Arrow on the piston? I don't know if the top end has ever come off before, though I suppose its possible. If it was serviced, I have no idea what was done, but it would have been over 15 years ago.

joeyrobots · « **Reply #8 on:** July 05, 2015, 09:09:21 PM »

I did find a replacement cam chain guide and payed a premium due to its scarcity. You think its possible was just too loose and jumped? And all this damage then is me just from putting off some basic maintenance for a few days. Thats just how it goes isn't it.

eigenvector · « **Reply #9 on:** July 05, 2015, 10:51:53 PM »

Hard to tell why in your case, but in my case I let the cam chain go for too long before replacing it. That tensioner can only do so much before the chain is just too stretched out - coupled with the wear on the tensioner and return guide and the whole system collapses quickly.

One of the reasons why mine went so fast was that the tensioner itself was pretty messed up, the tension bolt was no longer turning properly and the gear was jammed.

links56 · « **Reply #10 on:** July 06, 2015, 07:45:10 PM »

Also when the chain gets stretched and you keep adjusting the tensioner, you are changing the ignition timing. If i had to guess that's what caused all the carbon build up. When you put the new valve in make sure you pour gasoline in all of the intake and exhaust ports. Start with one or the other and set the head on its side, then fill them up and see if it leaks past the valves. There should be no leakage. Since you have all this apart make sure you clean all that carbon off and like I said check the valves. Once you post some pics we can tell you if you maybe should do more?? While you have it half tore down. As eigenvector said it's not that big of a deal to repair this stuff, we can help you along the way too! Alot of other timing chain guides will work in these motors or I have made them also. If the chain was that loose it may be time for rings.

jonda500 · « **Reply #11 on:** July 07, 2015, 02:46:49 AM »

Quote from: links56 on July 06, 2015, 07:45:10 PM

Also when the chain gets stretched and you keep adjusting the tensioner, you are changing the ignition timing.

Slightly changes the valve timing - doesn't change the ignition timing

joeyrobots · « **Reply #12 on:** July 10, 2015, 05:31:21 PM »

Sorry for the delay. I've been scraping gasket gunk for a long time and I wanted to get it nice and clean before additional photos. Methylene chloride took the carbon residue off easily. Perpendicular razor scraping with carb cleaner removed the gasket. There was impossibly persistent residue on the head so I did something people might hate me for, 1000 grit wet sand with a block. Checked it with feeler gauges this way and that way and can't get a .004 under anywhere. I still need to scrape the engine case surface, below the pistons.

The bent valve came out no problem with a homemade C-clamp device to compress the springs. The top ring on piston 1 and 4 were broken in half so those definitely need to be replaced. The gas poured into the exhaust and intake did not leak through the valves at all. Should i bother removing and lapping the existing valves? Cam chain sprocket looks a little banged up, thoughts? I also filed off the distorted aluminum around the cam chain guide slots in the block. I am worried about that giving me trouble.

I have new parts here now. New valve, new gaskets, new cam chain, new rings, new tensioner, new chain guide. I have to break the cam chain and rivet it i guess. Not sure if there is a diy trick for that, or what tool exactly to buy. I have read about the rubber band trick for the rockers when putting the cam cover on. Anything else I should really be attentive to here? The spotting in the cylinder jugs is just superficial from cleaning solvents splashing in.

thanks for all your advice.

eigenvector · « **Reply #13 on:** July 10, 2015, 06:25:18 PM »

Breaking the cam chain can be a royal pain in the ass. None of the chain tools commonly available will fit it. I can dig up the chain tool that will work well for this if you like.

As for the cam chain - I bought bulk chain from Amazon (common chain used in go-karts) and spliced it together with a master link. Makes reassembly of the engine so much simpler.

If you can get a new sprocket for the cam use it - that one is likely to chew up the new chain and probably is damaged in ways you can't see. Someone here has one I'm sure if you can't find one.

joeyrobots · « **Reply #14 on:** July 10, 2015, 06:29:22 PM »

I have an EK chain from 4into1.com for the cam chain replacement, they were sold out of DID. I just need to break it and rivet the master link. I used to fix bicycles and would break chains all the time, but you never had to rivet/peen them back, just mash the pin back through the linkage.

Yeah i will shop around for a cam sprocket. It does look a little chewed up. thankS!

links56 · « **Reply #15 on:** July 10, 2015, 09:43:58 PM »

Quote from: jonda500 on July 07, 2015, 02:46:49 AM

Quote from: links56 on July 06, 2015, 07:45:10 PM
Also when the chain gets stretched and you keep adjusting the tensioner, you are changing the ignition timing.

Slightly changes the valve timing - doesn't change the ignition timing

Yep, valve timing I meant nice catch!

links56 · « **Reply #16 on:** July 10, 2015, 09:57:55 PM »

Looking good, I would definitely lap the exhaust valves so they have a good seal just the ones that are leaking. I would also replace that cam sprocket as mentioned. What does the other sprocket look like? I know its more work but it doesn't make sense to replace the chain and just one of the sprockets. Re-work sucks.

scunny · « **Reply #17 on:** July 10, 2015, 10:06:46 PM »

the other sprocket is part of the crankshaft

links56 · « **Reply #18 on:** July 10, 2015, 10:14:34 PM »

Doesn't mean its not ate up too.

joeyrobots · « **Reply #19 on:** August 18, 2015, 06:52:21 AM »

Well everything is reassembled and looking great. Its also running great, idling better than it ever has. I replaced the cam sprocket with one in much better shape. Thank you for your help and advice.

However, despite everything, I have one major conundrum. I am getting major heat off the bike now. After running for about 45 min in 75-80 degree heat, the oil light starts flickering, and you can feel the heat on you feet, legs, etc. When i stop because I'm losing oil pressure as heat builds up, the temps on the engine are higher than they've ever been. If i spit on the clutch case, it sizzles so I'm well over 212 degrees.

I checked the oil levels, and I opened the valve covers to make sure I'm getting oil up top. Everything seems ok. I'm thinking this through, turning it over in my head, looking at what changed in the rebuild (new piston rings, gaskets, cam chain guides, cam chain, cam sprocket), what I could have possibly re-assembled improperly. But is just not adding up, I feel I was very thorough and cautious on reassembly. The bike was running lean after the top end rebuild, I could cold start without opening the choke. But i re-oiled the foam filter and turned in the air screws, so that doesn't seem to be such an issue anymore. I think I might change the oil again, in case there are any residual particles of cam chain guide and chain. But that doesn't seem like it should cause so much heat.

Any ideas what could be causing all this heat? Its a new phenomenon since the rebuild, wasn't an issue before. Anything I should look at?

jonda500 · « **Reply #20 on:** August 18, 2015, 07:24:47 AM »

I have heard a lean mixture can cause overheating (and eventually engine damage!) - do a mid ride plug chop to check for a lean mixture even though it sounds like it may be running rich when running on the pilot jet/idle circuit which would explain why it will start without the choke.

Maybe someone else here knows of more possible overheating causes? e.g. lack of oil circulation?

John

Tews19 · « **Reply #21 on:** August 18, 2015, 10:55:06 AM »

What oil are you running?

joeyrobots · « **Reply #22 on:** August 20, 2015, 07:33:12 PM »

Regular old dino oil. 20w50 Castrol 4T

eigenvector · « **Reply #23 on:** August 21, 2015, 09:45:20 PM »

That should be fine, a bit heavy really, but perfectly fine.

Have you removed the oil pan? Ever - I don't remember you saying? With that much damage from the cam chain I think you'd be amazed at what is clogging that pickup filter in the oil pan.

Just asking, there's a lot of places to examine after stuff like that happens. Certainly the pan itself is filled with debris from the cam chain guides.

joeyrobots · « **Reply #24 on:** August 21, 2015, 09:53:30 PM »

The pan was dropped and cleaned out, lots of little metal chunks. I wiped some glitter off the screen. I seem to have fine oil pressure. The oil light doesn't come on at all until it starts to get hot. I opened the valve covers and the rockers have a good coating of oil on them, plus no noise from the top end so I believe the oil jets up the sides of the block are working fine. I really don't want to pull the top end apart again.

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Author Topic: Broken Cam Chain? (Read 5132 times)