well may be some good news
changed the plugs and fired up the old girl, no change
took off the cam cover and found that one of the rocker arms had come off the exhaust valve on number 2 cylinder
the valve was therefore in the closed position and not letting gasses out
i will have to get one of those valve spring compressors that you use to change springs without taking the head off
here are some pictures
what possible damage might have been caused?
comments please
ditch
Rescued attachment DSCF0005.JPG
and another
a lucky escape i think..... the valve failed in the closed position
why would the rocker arm come off like that?
is there any way to stop it happening again ?
ditch
Rescued attachment DSCF0003.JPG
I got my donor cheaper as it was running in a similar manner and the guy had been told by his mates that he cam had gone.
The rocker was in a similar position to yours.
It can happen when you over rev and get valve float where the valve spring cannot accelerate the valve quick enough to remain in contact with the
rocker.
The law that states "anything not restrained will move to an undesirable position" is applicable.
It could also happen if the spring has reduced in free length, but I think the former is probably the case.
I replaced the rocker and ran trouble free after.
HTH
Excessive revs = valve bounce = valve open & cam closed (so to speak) = large gap for rocker to fall out!!!
Cure, don't over rev it!!!
You may be lucky as there may be other problems yet so I would still carry out a compression test on all cylinders
Martyn
the engine has only 800 miles on the clock so i think i will put it back on and then put a rev limiter on.
the engine spec sheet suggests that the engine can rev to 8000 rpm but i think valve bounce must have set in.
omex rev limiter here i come.
ditch
Why don't you just de-adjust it and pop it back on ??
quote:
Originally posted by ditchlewis
well may be some good news
changed the plugs and fired up the old girl, no change
took off the cam cover and found that one of the rocker arms had come off the exhaust valve on number 2 cylinder
the valve was therefore in the closed position and not letting gasses out
i will have to get one of those valve spring compressors that you use to change springs without taking the head off
need to find someone with the equipment to carry out a compression test..
still hoping that this is all thats broken. if so it was a timely warning
ditch
Turn the cam so that the offending lobe is pointing up. Start to re-insert finger from valve side. When finger meets with post give the valve end of the finger a light tap with a soft hammer to mount finger on ball stud. Refit retaining spring and check valve clearance. JD
Has it actually broken or just come off??
Sometimes they they just come off and do no damage ,can you not put it back on and try it and if still misfiring then do a compression test.
its just come off
there are no marks and i did over rev it a bit
its supposed to reach 8000 rpm but i'm not so sure. i'll put a 7200 limit on it, still very high for a pinto
ditch
Who built the engine? Unless you payed a lot of money for it (i.e. forged pistons, steel rods, ARP bolts etc. ) I would be very dubious of a safe 8000RPM capability. Pinto flywheels also have a habit of detaching themselves at those kind of speeds unless extra dowels are fitted, or the Cosworth crank with the extra bolts are used!
I would suggest checking that the valve isn't bent....
the engine was built by Vulcan engineering. it was ballanced and blue printed, with a lightened flywheel and double dowelled.
the spec sheets show 8K rpm with max power at 6500 rpm.
as you say 8K rpm is special and the valve bounce may prove 8k a bit fanciful..
i am planning to install a rev limeter with about 7K as a top rpm.
todays job is to put the rocker back in place and then rotate the engine to check that all valves move the right amount.
see if it runs and then do a compression test.
i'm hoping that i was lucky.
ditch
[Edited on 13/6/08 by ditchlewis]
If max power is at 6,500, why the hell would you want to rev it to 8,000 anyways? A little over max power maybe, but not that much.
thats what i thought, but the graphs show 120bhp at 8000.
ordered a rev limiter now and will limit it to 7000.
ditch
problem solved
the locking nut on the ball pivot had become loose allowing the cam follower to fall away from the cam. when the engine was reved the retaining clip
snapped and the cam follower fell off the valve . the valve failed closed and the engine expelling the exhaust through the inlet valve and the
carb.
i've ordered a rev limiter also as this was a very timely and lucky escape.
i will be having a compression test also just to check every thing out.
many thanks lads.
ditch
surely you should be able to judge the limit when accelerating to 7k. I'd be very concerned at a pinto at 8K.
Still atleast no damage, damage would only have occured if the valve had stuck open.
i help my mate run his sports 2000 pinto engined race car, that's built to rev to 8000, but again it's past peak power really. however he had lots of problems with tappet posts unwinding all last season, it was ok if he kept the revs below 7k. For this year we've stripped out all the tappet posts and locknuts, cleared out the holes, and used some hi temp, hi strength locktite, intended for sticking bushes into place on them. no problems since, but i'm not sure how we'll go about re setting the tappets!
Don't forget to reset the valve clearances if the rocker stud has moved!