john gill

Hello all

After a complete modified rebuild & ST retune I have had a problematic harsh engine noise creep into the running engine .It is more pronounced at idle but comes & goes if you raise the throttle .
It is very similar to a sticky hydraulic tappet but I would think slightly more heavy ,it is coming from the vicinity of the valves & only on one head ,& is becoming almost constant now ,but has come & gone in the last few weeks ,
could this possibly be due to the anti drainback valve having gathered some dirt ?

Also how much oil should be under the valve cover after the engine has been run ?

I am hoping someone can shed some light on this issue ,& possibly save a major pulldown

thank you all

jon928se

John

On the 32V engines the anti drainback valves, IMHO, never fail, or get clogged up with cr*p . What fails is the O ring that seals in hydraulic terms the cam and hydraulic tappet side of the valve from the open space around the cams - the cam box in simpler terminology.

The valve is simple - there's an oilway coming from the block into the head , which is sealed in the head for anti drainback with a ball that seats on a machined seat. the ball is pressed onto the seat by a spring. . The spring is held in place by a cylinder of alu that is held into the head with a little allen screw that screw from the outside of the head - near Cyl 4 exhaust port . The cylinder of alu has a radial groove around it into which fits an O ring. This O ring goes hard and leaks oil from the pressurised side into the cam box, thus reducing lube to the cams while running and also allowing the hydraulic tappets to compress when the engine is not running.

jon928se

PS

If the noise sounds like a kind of quiet rod bearing failure - that comes and goes - thats it.

If it sounds like a very quiet big end bearing failure it's the bearings in the air pump (if you still have have it)

john gill

Hello John

Doesnt have an air pump , the con rod bearings couldnt be worn as they are new , & only if there has been serious oiling issues , this engine was rebuilt from the ground up with serious modifications , it has seen up to 7000rpms & makes good power , I would have thought that if the bearings had issues it would show up as catastophic at these high rpms , but at the moment it is only evident at idle & slightly above ,
Hoping for a simple fix thanks for the info

jon928se

What I mean't by the sounds like a quiet rod bearing failure is that it is one or more tapppets that is not geting enough oil because the non returm valve housing in the head is leaking pressure into the cam box and thus reducing the pressure to the to (and also to the cam shaft)

jon928se

What I mean't by the sounds like a quiet rod bearing failure is that it is one or more tapppets that is not geting enough oil because the non returm valve housing in the head is leaking pressure into the cam box and thus reducing the pressure to the to (and also to the cam shaft)

Mrmerlin

what is the year of the car your working and the engine??

SeanR

Dump in some Marvel Mystery Oil. Could just be a stuck lifter. Mine makes a similar noise if it has not run in awhile.

Bill Ball

Bad lifter noises transmit and I have no good experience with diagnosing one externally, but I wonder if a mechanic's stethoscope held on each exhaust and intake port would alllow you to pinpoint it. If it tracks to one cylinder intake or exhaust port that would be evidence for a lifter.

john gill

Hello ALl

Car is a 90 GT , yes I am hoping that the valve is the problem otherwise I am in for a another pulldown

atb

Cam chain tensioner?

Kevin Michael

Would be my guess also. BTDT.

john gill

Cam chain tensioner appears to be ok ,
How much oil should be in the cam box after a run ??

Should there be minimal leakage ??

On the tensioner question , all appears ok ,but should you be able to press on the top chain & easily compress it ??

TIA
JG

atb

Hi John,

On the tensioners, I think if the pads are tightly in place and the hardlines are properly oriented you're good. Kevin might have more to add.