almost lost my head

[rob w]

The last time I rode my 400, it ran terrible, like it was very lean, it would backfire and detonate. Using the choke some would not help, it would start good, then had no bottom end and would only run at one throttle setting.
 I thought it was a main seal air leak from behind the flywheel. I pulled the motor out to go through it, and found that two head bolts were totally loose, and the other 6 were not very tight.
  Can the engine suck air in from the head if it is not properly tightened?
 Do these symptom's sound like a loose head?
 Is there a test I can do to check the R.H. main seal, to know it is'nt leaking air.
 You really have to watch the nuts and bolts on these 400's, eh?
Any imput would be appreciated
Bob.




 

[Jdbglover]

Bob,

The test that can be done to determine if the engine is leaking elsewhere, beside the the head is a preasure test of the engine. The following is a link to an article on how to build a pressure tester cheap and how to use it.

http://www.westcoasthodaka.com/psitst3.html


 

[john durrill]

Rob,
 Yes a leaking head gasket can do that. Replace the head gasket , while you have it off check out the cylinder with the piston all the way at the bottom of the stroke. Just to make sure  the cylinder walls look good.
 We found on both my 175 conversion and my sons 175 piner that runing the engine up to temp and then re-torqueing the head bolts was a must . We found over a very short time both heads would have loose nuts and a bolt if we didnt. the third time we checked them after a short ride they were tight and have stayed that way.
 If the right side seal is leaking, you can usualy see damp spots behind the stator base plate..
Having a setup to check crankcase sealing is a good idea though. its a handy tool to have around.
 John D.

 

[rob w]

John G. and John D., thank you for your guidance. It's funny how I only learn about these things through my mistakes, I've read a dozen times to re-torque the head bolts after assembly, but I have to suffer the consequences before it truely sinks in.
 The pressure testing tool seems like a good thing to have, does'nt appear to be too hard to make after purchasing the bulb and guage at NAPA.
 I've already got a new main seal, so I might as well install it now. But I'm leaning toward the head as being the source of the trouble, because the time before last, it ran beautiful. I'm guessing the seal would'nt go bad that quickly.
 My main target for this year is no DNF's, thanks again guys.


 

[tim bowers]

Barry Higgins told me one time to run
the bike up to temp. then let it cool down
completely and retorque the bolts again.
This was at an AHRMA national a few years
ago and I was having the same problem, infact
the whole assembly was loose(cylinder and all)after the first moto. After I did what he
said I had zero problems with that again