Cylinder Leak?

[jjk]

I noticed after riding yesterday my cylinder was leaking on the left side and the front of the motor. I haven't tried to tighten the bolts yet, I was going to get a manual tmrw and get the torque specs first. Is this something that'll effect the compression? Is it likely loose bolts or maybe a bad gasket? Any feedback would be appreciated. Thanks!

 

 

[YZbumblebee]

That can't be good. I'd start with a torque wrench and go from there. I'm not sure how finicky 4 strokes are about compression but you better bench her until you resolve this. If you haven't changed the gasket in a while its probly worth the small amount of money to take care of this.

[grayracer513]

A torque wrench will be no help.  The 450 head is angle torqued, not torqued by a numeric value, so you'd need to start over.  Even if the head was torqued to a number, retorquing never quite works right. 

 

Replace the gasket, and try to figure out why it leaked (heat?, etc.)

[jjk]

A torque wrench will be no help.  The 450 head is angle torqued, not torqued by a numeric value, so you'd need to start over.  Even if the head was torqued to a number, retorquing never quite works right. 

 

Replace the gasket, and try to figure out why it leaked (heat?, etc.)

Thanks, that's what I needed to know. Angle torqued? For example, like 90deg? Is this info found in the manual?

[grayracer513]

Thanks, that's what I needed to know. Angle torqued? For example, like 90deg? Is this info found in the manual?

 

Yes.  Also here: https://www.thumpertalk.com/topic/873863-cylinder-head-tightening/

[jjk]

Yes.  Also here: https://www.thumpertalk.com/topic/873863-cylinder-head-tightening/

Thanks for the info.. I'm assuming if I'm pulling the cylinder, I should probably do a compression test and see if I should replace the piston as well?

[grayracer513]

Conventional compression tests will tell nothing of any use.  First reason for that is that the bike has automatic decompression.  The second is that even without  that, cranking compression readings on a big inch single are far too variable, and you couldn't really even kick it through compression if it were completely healthy, anyway.

 

If you want a good picture of your ring condition, have a leak down test done.

[jjk]

Conventional compression tests will tell nothing of any use.  First reason for that is that the bike has automatic decompression.  The second is that even without  that, cranking compression readings on a big inch single are far too variable, and you couldn't really even kick it through compression if it were completely healthy, anyway.

 

If you want a good picture of your ring condition, have a leak down test done.

Thanks again for all the feedback. My buddy owns a diesel shop. I'll see if I can borrow a leak down tester from him...

[jjk]

Conventional compression tests will tell nothing of any use.  First reason for that is that the bike has automatic decompression.  The second is that even without  that, cranking compression readings on a big inch single are far too variable, and you couldn't really even kick it through compression if it were completely healthy, anyway.

 

If you want a good picture of your ring condition, have a leak down test done.

 

I was thinking, if the motor is already leaking oil, if I do a leak down prior to changing the gasket, it'll be bleeding of for sure, won't it? 

[grayracer513]

It might, or it might not, but the beauty of a leak down test is that you can tell what's leaking and how much.

[jjk]

It might, or it might not, but the beauty of a leak down test is that you can tell what's leaking and how much.

Sorry for all the questions, but I want to make sure I understand. I've not done a leak down before, when you refer to being able to tell whats leaking and how much, could you explain that? I realize the gauge will tell me how much, but as far as what's leaking, is that by spraying the engine with soap water or is there something else?

Edited May 5, 2014 by jjk

[grayracer513]

If the valves leak, you'll be able to hear it in the exhaust and/or intake.  If the rings leak excessively (they all leak because they have end gaps), that can be heard in the crankcase.  Leaks into the cooling system will blow bubbles out of the radiators.  That sort of thing.  If more than one thing leaks, it becomes kind of subjective as to how to grade the severity of any one of them. 

[jjk]

A torque wrench will be no help.  The 450 head is angle torqued, not torqued by a numeric value, so you'd need to start over.  Even if the head was torqued to a number, retorquing never quite works right. 

 

Replace the gasket, and try to figure out why it leaked (heat?, etc.)

 

Quick question for you if I can. I replaced the gasket and torqued it according to the spec. After doing so I realized the front chain guide wasn't properly positioned. I had to loosen the head bolts, slightly lift the head and re-positioned the chain guide. I torqued the head down to spec again. I'm hoping I didn't ruin the gasket in doing this, can you shed some light on this please? 

[grayracer513]

You cannot reuse a head gasket where the head's been torqued down and then removed.  It won't seal reliably. 

[jjk]

You cannot reuse a head gasket where the head's been torqued down and then removed. It won't seal reliably.

That's what I was afraid of. That sucks. Guess I better tear it back down. Thanks for the help.

[jjk]

You cannot reuse a head gasket where the head's been torqued down and then removed. It won't seal reliably.

It seemed like I had read somewhere that if it hadn't gone through a heat cycle it'd be ok, but that didn't sound right.

[grayracer513]

People have gotten away with it, but it's a low percentage bet.

[jjk]

People have gotten away with it, but it's a low percentage bet.

I'm confident you're right but I hope to be one of those lucky Sum B's.... I left it on, adjusted the valves and went out and rode for a few hrs today.. So far so good, the valves were definetly out of spec.. Hopefully my luck holds up. Thanks for all your feedback.. It's pretty obvious you've help a lot of guys out there... Thanks again!!