Rebuild Mi16 Missfiring - Help Required!

[Chris H 10]

I've finally got my rebuilt (not by me) mi16 up and running and it is missfiring on no2 cyl. When i first fired the engine up a couple of months ago it had a noticable rattle and shut it off after a few secs and quickly found the inlet clearances on no2 cyl were 0.45mm too big. Today I've fitted some shims the correct size and put everything back together as it was when it was built. The engine is the same spec as before the rebuild and is running the same map etc....its on omex and jenvey throttle bodies and is basically std except for piper cams and mechanical followers.

 

When i ran it up to day its missfiring on cyl 2 and i have spark, and if you swap the plug leads between cyl 2and 3 it makes no difference (dis system) i then swaped the injector plugs between cyl 1 and 2 as all injectors are fired as one batch. i then swaped the injectors between cyl 1 and 2 and still no change.

 

Any suggestions what to try next....planning to do a compression test tomorrow incase its a mechanical problem.

the only other thing i can think to try is to change the spark plug as they are brand new and you never know that it could be a faulty one.

 

Took the plug out of cyl2 and its much cleaner than the others, a little bit of soot but also wet with fuel.

 

There seems to be a slight bit of smoke comming out of the inlet trumpet on this cyl too.

 

Any feedback greatly recieved as i desperatly need to get this engine running as i'm doing a rally in a months time and am running out of time to run it in and get it fully mapped.

Edited August 16, 2008 by Chris H

[Chris H 10]

UPDATE

 

Just done a compression test and its not good

 

Cyl1 9bar

Cyl2 0bar (yes Zero)

Cyl3 11bar

Cyl4 10.5 bar

 

Bugger...bugger ...bugger!

 

Something must be seriously wrong with no2 cyl to have zero compression...i'll borrow the bore scope from work tomorrow to see if i can identify the problem but it seems like engine out and strip the head off.

 

i'm off to sulk!

[tony perks 1]

sound to me like the correct shims were actually Incorrect sized.

[Chris H 10]

Trust me i've tripple checked the shims sizes before i did anything and also got someone to check that i hadn't made a feck up! But i now think that maybe the shims were the correct size in the first place.......

 

I had a proper look with the borescope and the piston is showing sign of valve to piston damage so i reckon the valve has hit sligtly and isn't closing fully hence the bigger valve clearance. Not sure why this has only affected one cylinder though. With the cyl leakage tester thie affected cyl is 95% leakage and the other 3 are about 10% which is spot on....you can feel the air coming through the intake trumpet so there is deffinitelly a major problem with the intake valve sealing.

 

Better get the head off a have a proper inspection of the head and piston to see whats damaged.....maybe its time to get a propper head done.

 

I can't see me getting it ready in time for my next rally so i'll have to use my other car instead...shame its about 100bhp less.