Topic: Do i need to split cases

[kidrcth]

So last weekend i royally messed up. Don't ask, still a little pissed at myself. Anyways, i ruined a set of cylinders and pistons in the process.

While removing the cylinder, i found myself beating on one or two of the pistons with a hammer and a piece of wood to push it out. I had never planned on splitting cases prior to this but i find myself worrying about the rod and main bearings.

Part of me feels like an engine has an explosion in it all the time, but the other side tells me i need to check my bearings. Do you think the bearings are ruined?

I can be prepared to split cases, i really just didn't want to.

[Trad]

I wouldn't stress out too much just yet. Were the pistons seized to the cast iron bores?

[madmtnmotors]

Part of me feels like an engine has an explosion in it all the time

    

Not sure what you're trying to describe.

There are actually two "explosions" for every revolution of the crank... 

[HondaMan]

Well, my OCD may not help here, but...if I were beating on a rod, I'd have to Plastigage the bearings afterward. I can see how the top side bearing could take a beating and add some clearance in the process?

But, that's my OCD talkin'...

[Ravie]

"Don't ask" Are the details that would help people give you the best advice.

What happens during the process of combustion is a controlled burn, not just a bang explosion. Different forces at work.

[kidrcth]

"Don't ask" Are the details that would help people give you the best advice.

What happens during the process of combustion is a controlled burn, not just a bang explosion. Different forces at work.

you are totally right, but the process in which it happened is a bad story. not my best judgement.

[DaveBarbier]

Like Trad asked, were pistons seized? Wailing on it hard? Any idea if the piston you were wailing on was at TDC? I'd think there would be less strain on the crank bearings if it was halfway down the cylinder.

I've pulled up my proverbial chair. I'm in...let's hear the story.


---
1978 Honda CB550K

[martin_uk]

If the piston was seized in the bore, the resistance to movement would be between the piston and bore and not the con rod bearings/crank journal.

If you hit the piston then it could not transmit force until it has broken free of the bore.

You can damage the piston, but unless it is the bottom end that is seized, should not damage.

However, it does depend on the cause as there may be exceptions.

I just stripped a CB750K8 engine that PO had removed cylinders and pistons and all looked OK until I found a piston circlip in the bottom of engine !

[kidrcth]

OK, the easiest way to explain it is to first say it was a learning experience. You know how they say power tools and alcohol don't match, well never assemble your engine after having a few plus. Yes, life lesson. Anyways...

Piston ring when installed bent and somehow went into the bore almost effortlessly, however when I tried to spin the crank, the piston would not go up. After realizing I probably did something wrong I tried to remove everything to inspect and realized it was a much bigger task. In the process I broke quite a few fins, and the piston ring gouged up the cylinder pretty badly. So, to sum it up, DONT DO THAT.

See super dumb and expensive mistake.

[DaveBarbier]

If the piston was seized in the bore, the resistance to movement would be between the piston and bore and not the con rod bearings/crank journal.

If you hit the piston then it could not transmit force until it has broken free of the bore.

I'm thinking the old croquet move where you step on your ball while its next to your opponent's then strike your's and the opponent's goes flying. Since there is pretty much no play in the wrist pin I'd think the forces would transfer down to the bearing.

Kind of like hanging an axe head...anyone know what I'm talking about?


---
1978 Honda CB550K

[fmctm1sw]

See super dumb and expensive mistake.

  ...but not one to beat yourself up over.  I've heard of the rings getting snagged on install a few times now.  At any rate, it may be good to take a day or two break and get back to it with a fresh mind.  My 750 is going on 4 years of "steps backs" and "fresh minds..."   

[kidrcth]

See super dumb and expensive mistake.

  ...but not one to beat yourself up over.  I've heard of the rings getting snagged on install a few times now.  At any rate, it may be good to take a day or two break and get back to it with a fresh mind.  My 750 is going on 4 years of "steps backs" and "fresh minds..."   

I have a  pretty good start. My main goal for the near future is to finish the motor.

[fmctm1sw]

What's the history of the bike, do you know?  I had an old Twin I worked on and got the top and all nice and rebuilt.  I ran down the road with it and found it didn't shift into third gear.  In the end, the motor had to come out anyway.  Might be a blessing in disguise...

[kidrcth]

There is no history of the bike. There is only history of the Engine at question. Every piece of this bike has been assembled by me. Atleast to this point. When its done, no 2 pieces except the wheels will have come from the same bike.

The engine was purchased from a pretty good source i believe. Original owner, said it had like 7k miles on it. The bores looked to back this up also. Still had factory crosshatch.


Cant the gear shifts be checked? i can manually shift while engine is on stand.

[kidrcth]

Cases split, bearings checked. Everything was fine. Bearing show no mall wear and check to almost brand new specifications.