Skimmed head possible valve to piston clearance problem. Urgent.

Andrei "The Russian" · #1 16th September 2010, 10:18 PM

Have "new to me" Skimmed head fitted and after fitting cams and sprockets the engine wont turn past 8 degrees ATDC.
Im thinking that valve to piston clearance is too small due to head being skimmed.
Checked position of the cam sprockets and think they are on right.
Valve clearance is spot on as well.
Any one knows if a thicker head gasket needs to be used with a skimmed head.
This skimmed head was on a race bike but i dont know what was the set up on it.
Should i put my own head back on and check if engine spins ok with it first before i do anything else?
Any other ideas lads.
Need to get the bike ready in 4/5 days tops.
Thanks.

johnwalsh61 · #2 16th September 2010, 10:32 PM

Hi,
are the cams new as well?
Do the cam gears have slots for adjustment?
It's normal to use a thin gasket with skimmed head to get the compression well up unless the head has been skimmed too much, in which case it would mess up squish clearance. Most likely your timing is out, the kit cams need to be set up carefully

grahamh40 · #3 16th September 2010, 10:33 PM

i'd try the other head before doing anything
is the timing perfect? check it agen

Andrei "The Russian" · #4 16th September 2010, 10:36 PM

Originally Posted by johnwalsh61

Hi,
are the cams new as well?
Do the cam gears have slots for adjustment?
It's normal to use a thin gasket with skimmed head to get the compression well up unless the head has been skimmed too much, in which case it would mess up squish clearance. Most likely your timing is out, the kit cams need to be set up carefully

Im using stock cams mate with stock (non adjustable sprockets).
I should have adjustable sprockets tomorrow though.
I did look like it was skimmed a good bit but i was told that it was running on a race bike and i could see traces of head gasket on the head when i recieved it, so im sure it was working ok.
Probably the timing so.
Just not sure which way to adjusted it.
Bloody crap....
Thanks for the info.
ill see if i can readjust the timing either way so engine turns at least.

paulsmith · #5 16th September 2010, 10:36 PM

8 degrees atdc seems a very small amount, would not expect the valves (which i presume would be the inlets on number 4) to be open enough to lock the engine. i think you should go back and double check your timing. if you were getting a lock up then it would be happening when the piston would be approaching tdc. in your case, when number 3 is approaching tdc (presuming 1-3-4-2 order here, dont know for sure).
chopper obviously would be the man to ask, more experience than me
To view pics on this biker's forum - your post count must be 2 or greater.

Andrei "The Russian" · #6 16th September 2010, 10:38 PM

Originally Posted by grahamh40

i'd try the other head before doing anything
is the timing perfect? check it agen

Think timing is spot on.
Only one way it can go really to look right like in the manual.
Im thinking, since the head is skimmed may be timing of the cams need to be advanced?
I love working on my bike but this is just bugging the crap out of me.

grahamh40 · #7 16th September 2010, 10:44 PM

Originally Posted by Andrei "The Russian"

Think timing is spot on.
Only one way it can go really to look right like in the manual.
Im thinking, since the head is skimmed may be timing of the cams need to be advanced?
I love working on my bike but this is just bugging the crap out of me.

sometimes its nice t get someone else t do it.. worth paying someone, save the stress
To view pics on this biker's forum - your post count must be 2 or greater.
i wud of thought it would of turned over on standard timing? obviously not

grahamh40 · #8 16th September 2010, 10:45 PM

check it again to make sure..

2buckledrims · #9 16th September 2010, 10:45 PM

Advancing the ignition timing is one thing,but advancing the valve timing is completely different you dont want your valves opening to early

Andrei "The Russian" · #10 16th September 2010, 10:48 PM

Right, i think there might be a chance of pistons pushing on the head itself.
Taking the cams off and then see if it turns.
Thanks for the inputs so far lads.
I'll give ye an update later on.

Andrei "The Russian" · #11 16th September 2010, 11:12 PM

Update:
Engine turning fine with cams off.
Gonna put the cams back on and try again.

paulsmith · #12 16th September 2010, 11:14 PM

Originally Posted by Andrei "The Russian"

Right, i think there might be a chance of pistons pushing on the head itself.Taking the cams off and then see if it turns.
Thanks for the inputs so far lads.
I'll give ye an update later on.

still does not make sense, numbers 1 and 4 would be on the way down, 2 and 3 on the way up, you have already said this is happening 8 degress after tdc. the timing has to be out.
but, if you are right and the piston is hitting the head then it makes no difference wether the timing is out or not
To view pics on this biker's forum - your post count must be 2 or greater.

To view pics on this biker's forum - your post count must be 2 or greater.

Andrei "The Russian" · #13 16th September 2010, 11:44 PM

Update.
Intake valve on 4th cylinder is pushing the piston.
While piston #4 is on the way down the valve continues to open and thats when is makes contact.
I read somewhere before that valve to piston clearance is smaller after TDC compared to right at TDC.
Next step is swap the heads back and check it then.

paulsmith · #14 17th September 2010, 12:15 AM

just wandering, is the engine f2 or f3?? any danger the head is not compatible? the f3 had higher compression as standard, 12:1. piston design was different to accomodate........only a thought
To view pics on this biker's forum - your post count must be 2 or greater.

inlet opens 11 degrees btdc so contact definately possible (would imagine tuners use different valve clearances to compensate. have done this with cage engines in the past but i work on old classic ohv engines, not bike engines so dont quote me)

Andrei "The Russian" · #15 17th September 2010, 12:31 AM

Engine and the skimmed head are both off 1996.
Have the head off now.
Cleaning up my old one now to go back on.
The skimmed head is skimmed a lot, valves are sticking out beyond the surface of the cylinder head so i think it was skimmed too much.
Probably need a thicker gasket for it.
Just gonna put everything the way it was and then degree the cams to OEM spec and see where i am at.
Long night ahead of me. Better put on some coffee.
Thanks for all replies lads, really appreciate the help.
Want to do Mondello Masters as wont be racing much next year - new baby on the way. :-)

crispy · #16 17th September 2010, 01:22 AM

Originally Posted by Andrei "The Russian"

Engine and the skimmed head are both off 1996.
Have the head off now.
Cleaning up my old one now to go back on.
The skimmed head is skimmed a lot, valves are sticking out beyond the surface of the cylinder head so i think it was skimmed too much.
Probably need a thicker gasket for it.
Just gonna put everything the way it was and then degree the cams to OEM spec and see where i am at.
Long night ahead of me. Better put on some coffee.
Thanks for all replies lads, really appreciate the help.
Want to do Mondello Masters as wont be racing much next year - new baby on the way. :-)

That mean you might be selling the bike......

Andrei "The Russian" · #17 17th September 2010, 01:54 AM

Nah, want be selling it. Even if i was to move to a different class i'll always keep this bike.
Too much time, work and money gone into it.
One thing for sure - i'll be getting race prepped and tuned bike the next time instead of doing all the work and spending mad money on it myself.

Update:
Have my old cylinder head fitted, cams fitted - engine is turning fine.
Bloody e-bay, set me back a few hundred quid for nothing.
Anyway, better head to bed or my wife is gonna divorce me.
Thanks again lads.
I'll update this once i get it up and running, hopefully with some dyno figures.