chain broke crank case

[sedate]

Hey all, this is my first bike so very devastating to say and ask these questions. A mechanic recommended he weld this but it might leak oil like a Harley used to back in the day. Is this the best course of action? How would you guys go about fixing this? 

[Migyver]

Oh man, I'm sorry to see that, that's some bad luck.  Given the location of the break it's likely going to be difficult to stop it from leaking. 

I had a rock punch through my side cover on my WR on the stator side and had it bent back and welded, I put a piece of metal over it with JB weld, but it always looks slightly humid, not enough to actually leak, but it's a reminder.  This was on a straight piece without and bends, and bolts.

It's worth a shot if they say they can weld it.  Cheaper than a new engine.  Let us know how it fairs out.

[M. Hausknecht]

Sorry! This is why proper chain slack adjustment and regular chain lubrication are important.

I dunno what the chances for a good weld are, but I'd remove all the parts on that end of the crankshaft and give it a go. There is no pressurized oil around there, just splash off the gear you see that mates with the gear on the starter motor. Getting a level surface for the side cover and gasket is key to avoiding an oil leak. It should all be possible. The alternative is new engine cases, top and bottom, with everything removed from the broken case (and its companion) and reinstalled in undamaged cases.  Or, just replace the whole thing with a complete used engine. They seem to go for between $1500-$2500, when you can find one.  

 

Edited February 24, 2023 by M. Hausknecht

[Triple Jim]

It looks like the break includes a parting line bolt, so you'd either have to disassemble the engine to make it like stock, or you'd end up welding the case halves together.  Unless you just weld the top and side and use some sealer at the parting line, that is.

[Lone Wolf]

12 hours ago, sedate said:

 How would you guys go about fixing this? 

Looking at it strictly from a financial, detached, uninvolved perspective - the bike could be considered a "total loss" in terms of parts and labor to do a complete and proper repair to pre-loss condition. It sucks, but happens all the time when there is an expensive repair, or an otherwise perfect vehicle gets flooded with water.

Accordingly, if it was my bike, I would be willing to do a very strong band aid and just ride it.

In the old days, vehicles would get used to the point things needed to be rebuilt, and we would change bearings, grind valves, do whatever it took to keep "that" engine running. Today, for most consumer vehicles, we swap heads rather than do valves. We replace engines with either new or low mile used as others have suggested.

So if you look at it that way, the odds of splitting those cases (if this didn't happen) are really slim. I know it is not "proper" to join the top and bottom cases in a way they can't be unbolted in the future, but honestly that is not likely to be needed and you are already sort of perma-screwed.

I would clean the surfaces really, really well with acetone. Then do it again. I would get a short stiff brush, apply JB weld sparingly to both sides so that when pressed together it just forces out a small bead, like the diameter of string (not gobs of snot).

Before the JB weld sets up, I would have ready a new gasket for the side case, and install that to properly anchor the broken piece. The side cover may need to come off in the future, and with this repair that would be possible. Splitting the main cases would not be an option, but these engines can last hundreds of thousands of miles without needing to go deep into the engine.

The good news is that the piece that broke off does not hold bolts for a side cover. It really doesn't need to be strong enough to retain a fastener, just needs to be oil tight and be able to tolerate heating and cooling cycles.

[klx678]

22 hours ago, M. Hausknecht said:

Sorry! This is why proper chain slack adjustment and regular chain lubrication are important.

I dunno what the chances for a good weld are, but I'd remove all the parts on that end of the crankshaft and give it a go. There is no pressurized oil around there, just splash off the gear you see that mates with the gear on the starter motor. Getting a level surface for the side cover and gasket is key to avoiding an oil leak. It should all be possible. The alternative is new engine cases, top and bottom, with everything removed from the broken case (and its companion) and reinstalled in undamaged cases.  Or, just replace the whole thing with a complete used engine. They seem to go for between $1500-$2500, when you can find one.  

 

I'm not sure how much slack would have to be there to throw a chain, but it would have to be inches, not a half inch or so, but inches.   Incorrect chain alignment would be the other issue.  After all my dual sport is running around 2-1/2 inches of slack, otherwise it's too tight at the tightest spot, he Zephyr is 2", with proper chain alignment and neither have thrown or broken their chains.  Too tight would be as much a concern, because that would cause a chain to break or other damage.   

I had a chain break on the Zephyr, showing the link plate that broke had started cracking far earlier, being dirty in one area and clean in the new breakage.  That was when I did what was necessary to find out exactly what the chain slack should be.   I will now compress the rear suspension to get the countershaft, swing arm pivot, and rear axle in line, then adjust for about 1 inch of slack, then let the bike up to unloaded height and check the slack at that point to know what it needs, not what some manual says, that may have just been a cut and paste.  Chains are not meant to run tight.  It is better to have a bit more slack in the chain than not enough.   

The biggest risk with chains and maintenance newbies would be that they make the chain too tight or the chain line crooked.   I always check it both visually and with a measure from swing arm pivot to the axle centerlines.  

[M. Hausknecht]

Agreed @klx678 the biggest risks are too tight a chain and a rear wheel out-of-line. I didn't suggest too much slack as the likely culprit. The damage suffered by the OP is undoubtedly from the chain breaking, rather than falling off. 

[klx678]

@M. HausknechtI noticed that there wasn't any specific reference to why the chain adjustment was important, so I kind of stated what I'd learned and experienced. 

The only true thrown chain I ever had was when I was young and stupid, 19 y/o, and likely put the master link clip on backward on my Bultaco Sherpa T.  tossed a chain, jammed beteen the sprocket and ignition flywheel with a nice broken out piece betweent them.  Filled in with a thin piece of metal and some good epoxy that is still there after around 50 years.   

 

I forgot to say what I'd probably do.   I'd clean the area with some contact cleaner to get all oil out of the joint that is about to be made, then I'd epoxy the part in, with some Yamabond on the actual case joint (sparingly), and run it.  Looks like a low stress area.  See how it holds up and look for leakage occasionally.  Probably strip off paint on the outer area and fill in a bit with epoxy again just because.

[Lone Wolf]

27 years ago I was gunning a Harley Sportster, freeway on-ramp and broke a chain.

NEGLECT was the culprit. Although I was not a new rider, I was just riding the thing and only focused on keeping fresh oil in the engine, air in the tires. The chain worked, until it didn't.

We learn from our mistakes (or better yet, learn from other's mistakes). 

1 hour ago, klx678 said:

... I'd epoxy the part in, with some Yamabond on the actual case joint (sparingly), and run it.  Looks like a low stress area.  

Agreed, and those main engine cases likely would never need to be split. It's not a race bike.

JB-Weld is an epoxy, and well suited to this task (handles the heat, pressures, etc.)

J-B Weld™ is The Original Cold Weld two-part epoxy system that provides strong, lasting repairs to metal and multiple surfaces. Mixed at a ratio of 1:1, it forms a permanent bond and can be shaped, tapped, filed, sanded and drilled after curing. At room temperature, J-B Weld™ sets in 4-6 hours to a dark grey color. A full cure is reached in 15-24 hours. J-B Weld™ has a tensile strength of 5020 PSI and sets to a hard bond overnight. It can withstand temperatures up to 550ºF when fully cured.

[shinyribs]

On 2/24/2023 at 11:43 AM, Lone Wolf said:

Looking at it strictly from a financial, detached, uninvolved perspective - the bike could be considered a "total loss" in terms of parts and labor to do a complete and proper repair to pre-loss condition. It sucks, but happens all the time when there is an expensive repair, or an otherwise perfect vehicle gets flooded with water.

Accordingly, if it was my bike, I would be willing to do a very strong band aid and just ride it.

In the old days, vehicles would get used to the point things needed to be rebuilt, and we would change bearings, grind valves, do whatever it took to keep "that" engine running. Today, for most consumer vehicles, we swap heads rather than do valves. We replace engines with either new or low mile used as others have suggested.

So if you look at it that way, the odds of splitting those cases (if this didn't happen) are really slim. I know it is not "proper" to join the top and bottom cases in a way they can't be unbolted in the future, but honestly that is not likely to be needed and you are already sort of perma-screwed.

I would clean the surfaces really, really well with acetone. Then do it again. I would get a short stiff brush, apply JB weld sparingly to both sides so that when pressed together it just forces out a small bead, like the diameter of string (not gobs of snot).

Before the JB weld sets up, I would have ready a new gasket for the side case, and install that to properly anchor the broken piece. The side cover may need to come off in the future, and with this repair that would be possible. Splitting the main cases would not be an option, but these engines can last hundreds of thousands of miles without needing to go deep into the engine.

The good news is that the piece that broke off does not hold bolts for a side cover. It really doesn't need to be strong enough to retain a fastener, just needs to be oil tight and be able to tolerate heating and cooling cycles.

This ^ 

 

Or, if you want a more easily reversible repair, clean the area very well and glue the piece back in with Hondabond, Yamabond, Threebond...all the same stuff. 

The quick version of JB Weld kinda sucks. The original formula is extremely good stuff. I've got fuel tanks patched with original JB Weld that's 15 years old and still going strong. But the original JB Weld is very runny and can be difficult to keep in place on vertical surfaces for several hours as it cures. Threebond is very clingy and will stay put.  

 

ps- the rubber case saver/chain guard that fits inside the sprocket cover... reinstall it! 

Edited February 28, 2023 by shinyribs