Top end noise

[moon monkey]

Hi all, I'd like to take advantage of the massive knowledge here!

My engine (1975 2CV6) has started making a "ticking" noise -- louder than the normal noises I'd expect. It seems to be top-end, but isn't just the valves -- I've checked the clearances, and also changed from the 0.25mm I normally use to 0.20, without making any difference. The noise isn't there when the engine starts, but becomes apparent when it warms up. I wondered whether it was a rocker hitting the "Jelly Mould" rocker cover (which is what it sounds like), but I can't see any evidence of that, and I also tried running it with them only loosely on, again with no change. Lastly, I also tried running without the alternator belt, just to eliminate that. Apart from this noise the engine is running well, no other issues or clues.

So, I'd welcome suggestions as to what else it could be, so I can start checking!

[Davidm]

My 2cv engined Pembleton makes exactly the same noise you describe when hot and I too have failed to identify the cause so far !
Before fitting the engine I fitted new rings and checked the little end bearings but did not split the engine to check the camshaft or drive gear.
I've re-checked tappet clearances 3 times, and made sure the bolts locating the rocker shaft are secure.
The engine runs well so the incentive to dismantle more is not there yet.
Only tentative ideas so far and splitting the crankcase would be needed to check fully -
-the camshaft lobes worn or damaged somehow ? I could check the throw of the pushrods without dimantling.
-wear on the camshaft drive gear ? The gears are such that the same teeth always contact each other. I noticed on my spare engine that 4 or 5 teeth on the camshaft gear were pitted but the others ok. -but the sound is more like tappet noise.
-wear of the camshaft bearings ? but again the noise is rapid like tappet noise.

So I too would welcome suggestions !
Davidm

[Davidm]

Another (unlikely?) possibility I wondered about was a problem with the anti-backlash gear on the camshaft. Designed to reduce gear noise but what if a spring failed or the "floating" gear became stuck ?
But then the noise I get is unlike gear whine or rattly gears I think.
Davidm

[moon monkey]

Thanks for the thoughts, Davidm.

I've used a stethoscope and it's definitely louder at the top end. I did wonder about something in the pushrods -- so perhaps cam followers? But then I'd expect it to be louder the lower down the pushrod tube, which it doesn't seem to be.

But if it is something in that area, is there anything that can be checked (free play / clearances etc) at the top end, eg perhaps taking the head off but nothing deeper?

[Davidm]

The only test without dismantling I can think of is to measure the lift of the pushrods or valves as the engine is rotated.
Ken Hannah quoted some useful figures to help me choose a 2nd hand camshaft. The dimension over the lobes for an OE Citroen camshaft is 32.42 to 33.06 mm. I can't seem to find the dimension of the standard base circle but distance over lobe minus base circle would give the lift. Using a dial indicator on the rocker arm near the pushrod and preferably with valve clearance adjusted to zero the valve lift could be measured.
If the base circle is not known (eg if the engine has a reground camshaft) then the lift of the valves could be compared with each other and perhaps a dodgy one identified. Ken also advised that that the exhaust lobe nearest the front of the engine usually wears most.
David

[moon monkey]

Here is a video of the engine running. You can hear that the left hand cylinder (as viewed here) is noiser than the right.

Any suggestions?

https://www.totalrewind.org/lomax/engine_video.html

(note: if sound doesn't play, try a different browser -- chrome seems to not want to play sound! Or download it.)

[billp]

Hi Andy,
Sounds like a sticking cam follower, sticking valve, or loose valve guide. Before delving into the engine I'd swop the cylinder head with a spare. If you haven't got one then a fellow local club member could probably loan you one for the test. That would at least tell you if the problem was in your cylinder head, or lower down in the motor. Try removing the valves from the head, check if stems are bent, clean carbon deposits from the stem as they can run too tight in the guides, lifting the guides and making them noisy when they eventually seat as the valve closes. Another possibility is a bent push rod fouling on the inside of one of the tubes. I'd also check the poundage of the valve springs, as one could have lost it's strength, which could allow the valve to snap shut, if something was sticking somewhere. But a head swop will tell you where to look next.
Dished cam follower maybe.
Cheers
Bill

[Davidm]

We have had a couple of rainy days so I took up the suggestion of changing a cylinder head. In fact I changed both heads.
I refurbished the heads I took off about 2000 miles ago - I checked valve guides, ground in the valves and replaced the seals with new PTFE seals.
I have a spare engine and the cylinder heads were refurbished by our local excellent engine repairer. He used rubber seals because he thought the PTFE ones were tight on the valve stem. I fitted these cylinder heads to my engine in the car.
RESULT :-
The same noise is still there.
I now suspect the camshaft or camshaft timing gears.
Davidm

[motomallett]

HI running your engine with 25 thou tappet clearance would surely make your engine noisy regards Roger

[Ian Caldwell]

When I recently rebuilt the right side of my Avion's engine ( see the tapet replacement thread) , I found that my dad had set the vales to less than 0.15 mm. I've set them to 0.175, as per the middle range that the Haynes manual tells you, and I've certainly noticed quite a bit of extra noise coming from the ricker covers of both sides of the engine. Does anyone else run these engines with tight valve clearances? I know you can get burnt valve and other issues, which was not evident when my head was rebuilt, but it's strange that my dad had set them that way and apart from trying to cut the clatter down, I'm perplexed as he was a stickler for tolerances.

Ian.