Loud Knocking from front of Engine

[marshman]

Would be grateful for some Stag wisdom! After a trouble free thrash to Reading and back a couple of weeks ago I went to go out in the Stag and as soon as I started it up I could hear a loud knocking - similar to a bad big end knock but not quite as deep and solid. The oil pressure rapidly built up to 70psi and no difference.I popped the bonnet and determined it was coming from the front of the left hand head. I increased the revs and the noise increased with the revs though the volume and tone of it stayed the same. I decided to go for a quick drive to see if it changed as the engine warmed up - no difference!

Tonight I have removed the lefthand cam cover and checked all the valve clearances - they are all OK, the biggest being 20thou on one of the exhausts. I started it up, cold, with the cover off. The noise was very pronounced and definately not coming from the cam or any of the valves, but can be heard clearly coming from the depths of the timing cover. I removed the oil filler cap from the right hand head. The noise can be heard from there but not as loud as the left hand head side.

There is pleanty of oil flow to both cams, the cam buckets were still full of oil even though it had been sat for a week - so no issues there.

The speed of the knocking is in time with the cams - i.e about half engine speed. I have listened to the water pump and distributor. The distributor sounds sweet, the water pump also sounds oK but you can hear rhe knocking muffled in the background through a listening stick.

I suspect, but because I've never had it apart don't know, that it could be something to do with the jack shaft.

Any ideas/advice. Can the jackshaft be removed/checked without disturbing the heads/inlet manifold or do you have to remove the waterpump? Having replced the heads and seemingly got the cooling system sealed and sorted I am loath to disturb it!

Thanks in advance

Roger

[iani]

imported post

Have you checked the viscous coupling for play? I was amazed at what that sounded like, I thought I was in line for serious mechanical surgery.

Ian

[marshman]

imported post

Thanks Ian, I did check the viscous coupling and it is ok, This noise is definately internal to the engine -I got the engine ticking over at about 250 - 300 rpm and its still there with exactly the same volume and sound as at higher revs.

Roger

[Stagdad]

imported post

Hi Roger

70 psi seems very high,maybe the chain tentioners or chainshave been damagedas they are pumped out with oil pressure.

Cheers Steve

[marshman]

imported post

70 psi is cold though it doesn't drop much when hot but i can't seem to get it any lower. The chains seem OK. I must admit I am not convinced that higher oil pressure will do that much to damage the chains/tensioners. Anyway the noise is at camshaft speed, if it was some damage to one of the timing chains it would be a lot slower as the chain takes sometime to make a complet "circuit".

Roger

[stustag]

imported post

Roger

The pressure is very high it should be 50 psi at cold tickover decreasing to 25 psi when hot.

In one of Kingpin's recent (when he did them) articles he showed a tensioner that had failed due to high oil pressure (i think) and have worn grooves in the tensioner which had then cause the chain to eat into the metal guide plate under the camshaft sprocket.

Take the cam cover off again and with a powerful torch check everything just to make sure.

At 70 psi you will be putting a lot of pressure on the timing chains are you sure the relief valve is working ok?

Stuart

[marshman]

imported post

Hi Stuart,

The chains are new (< 1000 miles). I have spent many hours trying to get the oil pressure down and have now given up. 2 new pumps, different pressure releif springs etc. I have also discussed it with Peter at LdParts and he wasn't convinced that excessive pressure would definately spell disaster for the chains. I feel oil pressure and timing chain tensioners is one of those subjects that we will never get a definative answer too.:?

The knocking noise is too defined to be made by the chains. I had the engine running with the cam covers off and the chains seem fine, they track over the cam sprockets as smooth and true as can be expected. I checked the cam sprockets and they are tight.

I guess the next stage is to remove the timing chain cover and see whats there.

Thanks

Roger

[ams]

imported post

The only thing regarding the timing chains is that they are under greater stress and tension when a cam lobe is pushing down on a valve and so in theory any slack or issues with the tensioner could result in the sound occuring at camshaft speed in the chain or at the tensioner. I'd have a good gander inside the timing cover first.

Not wishing to be too alarmist but my only other thought was the possibility of a small end in one of the front cylinders if your sure it's not valve or cam related.

Hope this helps and all goes well

Andy.

[marshman]

imported post

Iam convinced the noise can't be made by the timing chains or tensioners, it is to definate, defined and regular. As it doesn't vary in tone or volume with engine revs or load, oil pressure or temperatureI have discounted big end or little end noise - also its at the wrong speed. It seems to occur once for every revolution of the camshaft - hence my question about the jackshaft.

Thanks for the suggestions, keep them coming.

Roger

[V Mad]

imported post

Hi Roger

Did you do replace the chains yourself or did someone else do the work?

Iworked on a car recently, and discovered a previous owner or mechanic had enlarged the adjuster hole to get more life out of the chains, and had not replaced any of the guides or tensioners. It was all in a terrible state, and one of the tensioners was about to break up.

Re your oil pressure, I cant see how you could get 70psi with a normal pump, so I wonder if your gauge could be lying?

Chris

[GDPR]

imported post

I'm wondering if you have a valve guide come loose...

[Bob Heritage]

imported post

Possibly have one of the tensioners at full legnth and slipped a cog?

[GDPR]

imported post

Crankshaft pulley bolt? Cam wheel bolts locktabbed but loose? Seized camchain link?

[richardthestag]

imported post

I think I had a very similar problem with my stag years ago. It started when the pressure relive valve in my old pump stuck and I had very low oil pressure at low revs.

I replaced the pump and everything went back to 50psi when hot at 3k rpm etc but I noticed a knocking noise. It sounded like it was coming from the front of the engine so I started fannying around with water pumps etc. I ended up removing/replacing a whole lot of stuff but only when I reinstalled the chains did I find one was stretched i.e. it wouldn't quite fit the cam sprocket on the n/s head so I replaced the pair. This got rid of the noise but afterwards I got thinking that maybe the knocking was caused by the extended tensioner against the stretched chain.

Prior to this whole sorry debacle I was running a hi pressure pump which gave 70+psi and had replaced it to cure the myriad of oil leaks that plagued my newly rebuilt engine.

Anyways read my story on my Stag website

http://myweb.tiscali.co.uk/rupertstag/

specifically my activities around May 2002

http://myweb.tiscali.co.uk/rupertstag/rh2002.htm

Good Luck - Richard

[bluestag]

imported post

check valve timing first to see if everything is lined up as it should be.

cheers Steve