Compression during break-in

6 replies to this topic
  • dw

Posted November 14, 2002 - 08:40 AM


I have been discussing this on swedish forums, but they have so low knowledge on thumpers on there, most of them are 2smokers.

I have driven my bike for that 1 (1) test hour & break in and operation checks that the manual recommends.

But when the kickstarter hits the TDC, i can move past that position just by Forcing it past with a little muscle... but from what i heard you should be able to jump on the kick starter on TDC without it moving past..

Now to the real question, is there a time during the break-in where the rings dont seal so well, so that air can slip past the rings when i push it with my hand, that its not fully broke in yet... or is something wrong?

Im really worried and you Gurus is sitting upon the answer :)

You guys always got the answers and by this message i must state that the spirit of this forum(s) are great, i would gladly help someone if i could *sigh*

  • Wicked_Crash

Posted November 14, 2002 - 09:14 AM


One thing you might want to check is the decompression lever. Make sure there is some free-play in the lever so that the cable is not too tight. It sounds to me like you are loosing compression somewhere, unless you compete in the world's strongest man competition. Keep us posted.

  • dw

Posted November 14, 2002 - 10:23 AM


I checked the play on the decomp lever, it got enough slack.

But still i can't stand on the kickstarter .. it will follow through. and i can push it down if i use force..

Any ideas? is something wrong ?

Cause everyone says you can stand on the starter without it moving, but i can't!

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  • michaeltrundle

Posted November 14, 2002 - 01:13 PM


nothing to worry about,
It took about 1000 kilometres before I could stand on my kickstarter without it just slowly turning over under my weight. Once its fully broken in your compression should increase as the rings bed in.
If its still running ok then it cant be that bad anyway.
see how it goes after a few good hard rides.

  • Wicked_Crash

Posted November 14, 2002 - 01:21 PM


Check the decompression linkage on the head, maybe something is sticking there. Make sure your spark plug is tight and check for oil leaks everywhere. It could also be a valve problem or they may already need adjusting.

  • dw

Posted November 18, 2002 - 08:06 AM


Hehe no leaks, no sticking, spoke to yamaha, the bike is fine, if your around my weight you can't stand on the kick even if its broken in, thats a fact :D im 110kg.. quite heavy :) but anyways, ill run it about 1000km before i do anything about the compression, the valves need to be checked for clearance after 1 hour? the manual says 1000km.. so i think i will not quite yet :D

  • R_Little

Posted November 18, 2002 - 10:28 AM


I would ride it a bit more and check again.

If the valves are getting tight it won't idle and loose power. If the bike runs okay, change the oil and ride it some more. Check valves after 10-15hrs or so.

I could force the kicker down with my hand on my WR400 when it was new too.

When I checked my valves after break in only 2 were .001" tight.

No problems in a year of riding.


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