Cracked my cylinder head

Damn, well I turned the motor over with a valve shim tool in place. It had been weeks since Ive had a day off of work or had touched the bike and somehow I stupidly overlooked the fact that the tool was installed. D:

So now that I need a new cylinderhead, is there any specific type I need or will any 750 head work? Anything in particular to do other than a valve job? I guess I may as well replace the rings while I have the head off. Any suggestions or info is much appreciated.

 

Ouch, that sux. Sorry to hear, 'specially since it's one of those ' d'oh, i should have known better' moves.

Good luck, hope it's an easy find and fix.

 

you can't access the piston rings unless the cylinder jugs are off. The cylinder head and cylinder jugs are two separate components. Also replacing original piston rings gets expensive, just sayin from experience.

Replacing the cylinder head is an easy swap, but definitely have a service and/or factory manual as a guide. Don't be ashamed either; I've cracked a corner piece off my cylinder head just by over-tightening the valve cover. I must've been too strong for my own good at that time

 

Golly.

Moellear is absolutely right, you don't need to touch the rings/pistons to swap the head. If the motor was "tight" there's no need to touch the "jugs."

All of the USA-market 750s used the same head. Find a decent one on eBay, get a valve job done on it (or do it yourself) new valve stem seals and you're good to go. You'll need a head gasket, and the o-rings for the oil passages. I would also highly recommend a new cam chain gallery seal, as the original is probably baked useless at this point, being 30 years old and all.

A quick tip: anytime I leave a repair or service procedure "in progress" I leave myself a note (usually a 3X5 post-it stuck to the speedo face) reminding myself where I left off (for instance "NO OIL IN MOTOR" or "REAR AXLE NOT TORQUED.") Saves on disasters, especially with multiple bikes in the garage.

 

I have that tool and it stays in my toolbox. I can't remember what I had for dinner half the time, and that tool scares me. I use a strand of 14g insulated wire for valve adjustments.
Sorry for your bad luck.

Dave

 

Sorry to hear of the disaster, not good at the beginning of the season Hope you can get her sorted before the really decent weather kicks in.

I'm fortunate to be blessed with a mind that automatically retains all kinds of useful information when working on engines etc, for example I stripped a ride on mower with Briggs & Stratton flat twin engine (for stripped crankcase threads) and then the guy bought a new mower so it stayed in bits for 3 years. He recently decided to clear out the workshop so asked me to have a look & surprisingly (even for me) I was able to put it all back together after making sleeve nuts for the crankcase, with no bother... 80

Point being, even knowing this I like to do as Fitz does & make notes of any potential dangerous/damaging things that were left undone on a part-finished job in case I don't get back to it soon.

Another good tip I sometimes do would be to put a zip tie around either the bike or workshop key, such that you have to take it off before you can turn the lock & it reminds you that you need to look closer before jumping in & getting on with the job.

Best of luck getting it sorted. Perhaps you could keep the head/broken part & see if anyone local could TIG weld it up once it's off?

 

Finals are next week and after that I'll have my days off of work to get the Seca fixed up. I think for now Im gonna attempt to temporarily adhere the two broken pieces in place to test the rest of the bike. I've invested thousands now into this bike, countless hours and it hasnt moved in two years. I want to make sure the rest of the bike is functioning before I invest in an engine rebuild.
In the meantime I'll start trying to source a head and get with my local machine shop. Should I replace the timing chainwhile or related components while I have the head off? I had a suspicion that the cam chain was occasionaly rubbing the valve cover before I started tearing the bike apart.
And the reason I wanted to replace the rings is that my compression is only 120psi. I also have receipts from the PO going back to 1994-95 saying the compression was 120. I suspect that either my rings are worn or my motor has mixmatched parts(the actual block with the cylinder jugs has some non stock black paint in the crevices and the valve cover was repainted black).

 

sorry to tell you that this probably won't be a smart decision. Could it be done? yeah but I wouldn't bother unless you know that the broken part is securely mounted and doesn't leak oil when the engine is operating. And if you did get it securely fitted back into its cracked position, then why bother getting another engine head? I put a crack in my engine head (previously explained) and thought I could just JB weld it back... it didn't hold very long so I wound up swapping heads. Fix it right the first time

Check the valve cover. If it was in fact rubbing then the cam chain tensioner wasn't set accurately. Not sure if you would have the auto-tensioner so I'm not much help with that regard. But if you were to replace the chain (timing chain & cam chain are the same chain) you would have to split the engine which I don't suspect you need to.

Have you read into how to remove engine head yet? its fairly simple yet I think you want to do more than you realize you even need to... you need a manual to understand & follow the easy steps on swapping engine heads.

120psi is average so I wouldn't consider changing the rings. As long as it was consistent across all four cylinders

 

Holy sh*t! This is serious damage.

I wouldn't even bother trying to fix that head...

 

Get rid of it. Get another. You'll spend more in trying to fix it than if you just pick up another one..............

dave F

 

I just want to ride it a few times to see if the forks, brakes, carburetors, tires and entire electrical system work since I just rebuilt them. The only reason why I think it would possibly hold oil is that the valve cover bolt-hole is located on the piece that broke off which would keep the piece in place.
Trust me I have no intention of riding it around town with an engine held together with rtv.

I have the manual, nothing in the manual looked complicated except the gearbox. I guess I'll be able to tell a little bit more about the condition of the motor once I get the head off.


@hogfiddles- Pick up another? Bike, motor, head?

 

This might be a place for JBWeld to actually work;

provided you can get both mating surfaces excruciatingly clean.

I wouldn't count on it for a long-term fix, either; but it may hold well enough to do the "testing" you envision.

 

I have a head sitting on the shelf - - if needed

PM sent

 

a good TIG welder could make that go away pretty easy