Topic: Went to look at a 78 750 tonight and...

[benjamin550]

...learned why o-ring chains can be very bad.

The bike didnt have a chain on it when we got there and the owner went to fetch the chain to show us that he had it.  As soon as I noticed it was an O-ring chain I had my suspicions on why oil was pouring out near the front sprocket. After I got the sprocket cover off I could see the chain grooves and the oil leak. Im curious to know what it would take to fix this. I have no idea what the correct part names are so I took a photo (bad cell pic) to try and show. The leaking (red circle) is coming from what looks to be a joint where two pieces of the engine come together, but im not sure what pieces they are and if they are repairable. Im guessing there is a gasket in between them. The grooves didnt look deep enough to go through the metal so maybe they just ate through the gasket?

Im trying to figure out what the bike is worth. He was asking 700, but that was before he knew about this leak. The good news is that the stock exhaust was in great shape and the side covers were too.

Thanks,
Kohl

[Skunk Stripe]

Something else caused this. The 78 CAME stock with an 0-ring chain. So, in order for this to happen, the chain was either really stinkin loose or there was a much too large sprocket on the front.

[phil71]

either way, you're talking about some real surgery to do anything but a half-assed fix that will only leak slightly less than it does now. however, for the time being, motor oil is still pretty cheap.. how fast does it come out?

[benjamin550]

Well, he did mention the chain was a loose too. I thought it was most likely form the o-ring chain since I had read quite a bit about them causing problems.

The leak is pretty significant. I certainly wouldn't ride with it like that. In less than 5 minutes of just idling it made a puddle about the width of my fist.

[Eydugstr]

After I got the sprocket cover off I could see the chain grooves and the oil leak. Im curious to know what it would take to fix this. The grooves didnt look deep enough to go through the metal so maybe they just ate through the gasket?

Im trying to figure out what the bike is worth. He was asking 700, but that was before he knew about this leak. The good news is that the stock exhaust was in great shape and the side covers were too.

Thanks,
Kohl

either way, you're talking about some real surgery to do anything but a half-assed fix that will only leak slightly less than it does now. however, for the time being, motor oil is still pretty cheap.. how fast does it come out?

Ben550 - I just got done finding/fixing a similar problem on my 750...


What phil71 said is spot on...Sure you might be able to jb weld it from the outside, but my guess is that'll still leak.  The PO on my bike went to the trouble of taking the motor apart, welding a piece onto the bottom half, jb welding the top, grinding them both flat until they fit together...and it still leaked...My solution was to find a set of good crankcase halves on ebay, and swap the motor's innards into the better cases.  It's fixable, but it's definitely a PITA...

[dave500]

offer him less,point out its screwed.

[CHIZZLE]

If the stock exhaust and side covers are in "great" shape that's worth $700 right there.  Just sayin'

[dave500]

youve got to haggle!!!!its not the same if you dont haggle!

[KingCustomCycles.com]

I paid $100 for a friend of mine to properly prep and weld that area on one of my chops.  It turned out beautiful and the weld bead was continous and flawless.  = no leaks.  He did say the worst part was torching out the old JB weld.

[CycleRanger]

Hard to tell from that photo but that drive sprocket looks completely shot.

[benjamin550]

wouldn't it be bad to weld it because its at a spot where the two cases meet? Wouldnt you essentially be welding the cases together.

When i showed this to the owner he understood that he would have to take a LOT less for the bike now. I would think somewhere in the couple hundred dollar range as its essentially a parts bike now. I think its worth a few hundred, and it did have stock exhaust in pretty good condition, but i was looking at the bike for my uncle and for him its too big of a job even if we got the bike really cheap.

[Don R]

OK, then tell us where it is...

[benjamin550]

don-

the bike or the leak?

The bike is in knoxville, tn if thats what you meant. If your referring to the leak, see picture.

[nayto550]

wouldn't it be bad to weld it because its at a spot where the two cases meet? Wouldnt you essentially be welding the cases together.

When welding the cases to fix a leak like this, you would have to completely disassemble the motor, weld, then machine to fit.  Otherwise, yes, you would be essentially welding the cases together.

[MCRider]

Well, he did mention the chain was a loose too. I thought it was most likely form the o-ring chain since I had read quite a bit about them causing problems.

The leak is pretty significant. I certainly wouldn't ride with it like that. In less than 5 minutes of just idling it made a puddle about the width of my fist.

What you had likely read was directed towards 500/550s which do not have the room for an ORing chain. Installing one will cause a problem like what you have encoutered.

However as stated, the 78CB750 came with an ORing chain, and all CB750s can be retrofitted to ORing chains in the 530 size for the older bikes and as replacement chains in the 630 size for the 77/78 models without consequence and I think its a big improvement.

Something other than the chain itself caused your problem.

[Roach]

Hard to tell from that photo but that drive sprocket looks completely shot.

thats the first thing i looked at there are no teeth or very little probably why the chains slapping

[seanbarney41]

It is a very common problem with 750's because they eat chains up pretty good and people get sloppy with chain and sprocket maintenance...then the chain breaks and gets jambed in there by the sprocket and the case cracks.  My bike has the same problem but it never leaked that bad.  Then I jb welded it...leaks a little less...but still leaks...at least my sidestand will never rust

[Doggie]

I have heard of the chain link ( where the chain is connected) put on backwards doing that kind of damage. Can anyone verify that?
                               Doug
                                                   

[dave500]

only if it lets go.

[ekpent]

That has to be the worst counter shaft sprocket I have ever seen. Surprised it stayed together as long as it did.Now look at that and then wonder to yourself ,Hmm did the guy ever change the oil or do any maintenance at all.

[Old Scrambler]

+1 on the really BAD sprocket.........................If no damage and condition of the bike is good, its likely worth something in the teens...$1700 or so.....................So buy the bike for $200-$400 and spend the difference to fix it up.................labor and welding about $400.............chain and sprockets about $200.........plus beer with your uncle.