I'll name that nasty metallic clatter in........?

[Mike Nevitt]

I’ll name that nasty metallic clatter in ……..?

I’m in urgent need of help please? My 1976 Stag suddenly stopped with a nasty metallic clatter just after starting and whilst idling. Subsequent investigations revealed that a small piece of metal had been ingested into number six cylinder which resulted in a bent inlet valve. I have since taken off the heads and replaced the valve, gaskets etc. (I also fitted new timing chains sprockets etc). The damage in the affected cylinder was a light fine half moon indent on the piston and two very small scuffs on the head itself. There were no marks on the valve itself or on the seat and the valve guide seemed fine. I confess, I took a gamble at that point. I did not do anything to the bottom of the engine or skim the heads. In spite of my very careful reassembly with all new parts the restart has to be judged a failure. Whilst it started and ran rather well it now has a new but very nasty metallic clatter, or tapping sound. I’ve been over it with a stethoscope and cannot narrow it down. I’ve uploaded a short 28 second video clip to YouTube under the title “I’ll name that nasty metallic clatter in ……..?” Not an easy challenge I know but I could really do with some help, guidance and advice please.

[KOY 23]

Hi Mike.
My guess is it’s cam buckets or valve clearances. Where are you in Devon?
John.

[DJT]

https://youtu.be/MpnbwfJaLZs

[Mike Nevitt]

KOY23. John good evening. I did wonder. I’m on the Devon, Somerset, Dorset border. Any help or advice would be hugely welcome. Thanks

[flying farmer]

Half moon dent in the piston sounds suspiciously like a bit from one of the spring washers that hold the air filter box to the carb elbows. Did you find one missing when you removed the air box?

Sometimes its a piece only a few mm long, I have heard of this happening before.

Its possible that there were a couple of bits in the inlet manifold, and if you didn't make sure it was cleaned out it is possible the second bit is now in a cylinder.

[marshman]

First question did you find the source of the metal piece?

It could be mal adjusted valve clearances. Did you use the same thickness head gasket - thick if the heads have been skimmed?

Second did you check the cam buckets on No. 6? not only visually but for fit in the bores? a slight bit of wear resulting in the cam bucket rocking in the bore can give a "knocking" sound.

Must admit the audio makes it sound more "light knock" than "tap" through my speakers if you know what I mean, trouble is the recording does alter the sound.

Whilst a stethoscope is good it seems to be almost useless on Stag (and Dolly Sprint) heads in pin pointing valve train noise - I had a worn cam bucket on my Sprint but even with the stethoscope right next to the offending bucket you could not determine that was where the noise was coming from. I confirmed it was by swapping it out for a good unworn one.


Does the noise change as you increase the revs, does it change as the engine warms up?. To be honest it sounds very much like my engine did - eventually after pulling the engine I found it was "piston slap" (thanks Wilf !), no. piston skirt was badly scuffed. It started suddenly on morning when I started the car, was fine the day before when I came back from a long run. The noise was very pronounced when cold and reduced as the engine warmed up, but never entirely went away. This was back in 2009. There are a couple of clips below - ignore the fact that there were 3 "click nothings" before the car started in the first clip - that was sorted by refacing the contacts in the solenoid!

Click on the pics below they are videos with sound.

[KOY 23]

Mike.
Have you access to a bore scope to look in the cylinders for other foreign objects/damage?
John

[jbuckl]

Would be helpful to hear it being revved up a bit.
From what I could hear…. Which is by no means definitive… it’s a loose valve guide , worn little end or piston slap.

my money would have been on little end …. But previous info wouldn’t rule out the others.

favourite noisey little ends are 6&8… they get the highest amount of dirty oil thrown up to the piston underside.

Little end bearing does not take a lot of wear (unusual in a stag) before it gets noisy & it does happen.

Fix is a new bronze bearing & very very accurate honing. May need a new piston pin aka gudgeon pin too.

A reamer cannot achieve the specified tolerance…. Only a honing machine can (e.g. sunnen machine)

[DJT]

Just to add a bit more information to the original post. Mike lives about 20 miles away and I was present at first start up after he had spend quite a lot of time stripping the heads and carefully refitting them with new thick gaskets, quality chains, new sprockets, etc. When he originally removed the heads, I removed the bent valve for him and could detect no discernible play or looseness in the guide. I would have been happy to fit a replacement valve and re-use the head.

Before the engine was started, we span it over for some time with plugs out, then again with plugs in but HT king lead disconnected. There was no sign of any knocking or unusual noises. The knocking was noticeable once the engine had started. To me it sounds as if it is within the block. I cannot detect any unusual noises from either head using a long screwdriver as a stethoscope. The noise increases in frequency as the revs increase.

[marshman]

Just to add a bit more information to the original post. Mike lives about 20 miles away and I was present at first start up after he had spend quite a lot of time stripping the heads and carefully refitting them with new thick gaskets, quality chains, new sprockets, etc. When he originally removed the heads, I removed the bent valve for him and could detect no discernible play or looseness in the guide. I would have been happy to fit a replacement valve and re-use the head.

Before the engine was started, we span it over for some time with plugs out, then again with plugs in but HT king lead disconnected. There was no sign of any knocking or unusual noises. The knocking was noticeable once the engine had started. To me it sounds as if it is within the block. I cannot detect any unusual noises from either head using a long screwdriver as a stethoscope. The noise increases in frequency as the revs increase.

Your description of the noise sounds like my engine. Ended up being pistons "slap" from a piston with a scuffed and damaged skirt. The first indicator that it was a piston problem was when I had the heads off and was cleaning of the top of the block I noticed no. 2 piston was sticking up proud on one side. You could rock the piston significantly more than any other piston. After removing the engine, stripping it right down, honing the bores, new pistons etc. all was fine. Spent ages chasing round after valve clearances, cam bucket wear, timing chains and tensioners, jackshaft end float, water pump, distributor drive, crank end float etc.

[Mike Nevitt]

Good evening and very grateful for the thoughts thus far. As requested I have now added a second YouTube clip entitled “Stag Clatter 2”. It shows a cold start and revving. I might add that I chose not to touch more than I had to so for example I checked the valve clearances but, as they seemed within tolerance I left them alone. I did change the Jackshaft sprocket and did slip the distributor out and back in, marking carefully as I did. However the water pump was not touched other than to be drained of course. My thanks to everyone, but DJT in particular. I really need to know where to start so all and any suggestions are worth their weight in gold. I know one of you will know.

[DJT]

https://youtu.be/Mi4MIJtwdJQ

[wilf]

Very difficult to say, but the noise on your video still seems to be a "light tapping" to me, rather than a knock, and so I think, in your shoes, I would recheck the valve clearances as a first step. Plus a borescope down each cylinder to ensure nothing is in there that shouldn't be. The very best of luck with this.

[KOY 23]

Thank you Wilf for endorsing my earlier suggestions,
I would also suggest a compression test to ensure no more bent valves,
Check that all cam bearing caps are in the right order on the correct heads.
Check valve clearances.
Remove cams and check for worn buckets.
Check valve collets are seated correctly, and buckets are not hitting the head.

[Mike Nevitt]

Ok well thank all very much. This thread seems to have gone cold so I will take all your suggestions and work my way through. I’ll let you know how we get on.