Broken piston ring? (longish)

You say when the ht lead is removed from No 6 cylinder the ticking stops , there couldn't be a hairline crack in the plug lead suppressor cap that is shorting to earth could there ??( a spark shorting to earth does make a sort of ticking sound)

If the caps are the same as the ones on the S14 Two of mine were cracked one so bad it atually broke off when removing it from the plug

cheers

Andy

How old are the shims that are fitted? It may be possible that the shims have become worn around their circumfrence and therefor connecting with the lip in the top of the bucket as the cam comes around.

Steve

Hi Ian,

 

You say you’ve just changed the head……was the sound there before or only since you’ve changed the head?

With the compression readings you are getting you wouldn’t normally associate anything wrong with the compression rings, particulalry as the readings are so close to each other.

It does sound like tracking from a plug, but I’d guess you’d lose power under load, (may not be discernable due to the copious amounts of power available), how does it behave if damp?

 

Is it there at tick over – no pun intended? If it is, have you tried looking at it ticking over in the dark?

 

What oil are you running, is the sound more noticeable when hot? I guess it’s not petrol related ‘pinking’ or ‘tinkling’, as that should affect all cylinders.

 

How good is the head rebuild? Could it be one or more of the valve/bucket assemblies are out of tolerance?

 

Reading your mail again I’d go for the plug cap/lead. I’d start by changing the plug and cover/lead before doing anything else. Try one thing at a time. It's the easiest thing to rule out. I'd then try a different fuel and then give it an oil change before I went any further. I'd also make sure the cooling system was working efficently. 

 

Dave

Nick wrote: I would not expect to see such an even spread of compressions if one had a broken ring.. and also the sound going away when the spark is disconnected makes me think that it is valve related.. the force of the firing making it move in its seat.

Hmmm.  Hadn't thought of that.  Guides are new and seats/vales were recut after guides were fitted and hence centralised in the seat.  Or so I was told. 

 

heres a little tip worth trying:

     
Diagnose Noises with a timing light

Valve train noises occur at half of crankshaft speed
so even if your ear can't tell whether the noise is
happening at 700 rpm (raps per minute) or only 350
rpm, your eyes can. Hook the timing light to any one
cylinder and watch the flash illuminate the timing
mark. Stare at it for a while and see if the flash
matches with the noise (i.e 1 flash for 1 tick). If it
does, then it is more likely to be , lifters, camshaft,
cam bearings, timing chain and gears.
If the noise seems twice as fast (i.e 1 flash for 2
ticks )it is more likely to be the crank, mains, rods,
rod bearings, wristpins and pistons/ rings.


Thinking about it, you already know it stop when you
pull the lead. You said you used 'Total Seal' rings,
did you use the correct honing pattern? it is possible
a ring hasn't seated properly. I've heard countless
stories of people who have had nothing but trouble
with TotalSeal rings.


Edited by 215DMX

215DMX wrote: heres a little tip worth trying:       Diagnose Noises with a timing light

Good idea.  That should pinpoint the area to conentrate on.  Just need to find a local motor factors that actual stock timing lights!!!

Thanks

Ian

 

SHEPSM3 wrote: Is the same noise eveident when the revs are comming back down?

Yes

 

Andy S wrote: When you put the head on what were the bores like? i had a ticking noise with an HSR Chevette years ago The block was rebored but number 4 bore was not bored enough and got too hot and caused the small end bearing to seize and this was the noise. I still have the piston with a big score mark down one side of it. The bore on number 4 was scored as well.  Not what you want to hear but just another suggestion.

Bores were fine.  Engine was previously rebored 8k miles ago and when I swapped the head the bores showed no signs of wear.  Thats not to say that something hasn't happened after fitting the new head but with the compression readings as they are I would see bore wear.

Incidentally I have carried out a cold compression test and get the following results

170,175,170,177,178,185

I did a repeat test as well to ensure repeatability of results.

No 6 cylinder on a hot test showed 188.  Why would no6 be the highest on the cold test (by a good margin) but only increase by 3 psi on the hot test whereas the others increase by around 6-8 psi on the hot test.  Can't make sense of it yet.  To test with the timing light as well so I can determine if it's top or bottom end.  Looks like I will run with it for now as the car will come off the road in winter for 6 months which will give me time to whip the head off again.

Thanks

Ian

 

SHEPSM3 wrote: ian M635UK wrote: SHEPSM3 wrote: Is the same noise eveident when the revs are comming back down? Yes   Well, that blows what I thought it may be out the window!

 

injectors? - noisy but not the problem

Ian,

When you fitted the pistons, did they have circlips to retain the gudgeon pins?  I rebuilt my M30 2800cs engine years ago with a set of Hepolite pistons (I was only 16!) and all ran well for a while. I ran the engine in well, but was having a high speed blast, cruising between 110 and flat out for about half an hour with an XR4i (in period) and had a minor disaster.  Light thrashing noise from the engine, which made me back off and stop as soon as I could.  From then on the engine had the same ticking of which you speak.  Most noticeablein the 1500 - 3000 rev range.  I can't speak for higher speeds, as I stayed slow till I took the head off.

My car looked OK on a dry test, but show problems (also pot 6) on a wet test.  Turned out one of the circlips had broken, and the head with the eyelet had found its way down the bore, past the rings.  Rings were not actually broken, but had a nick out of them, and the bore was scored.

I think for peace of mind you are best pulling the head again. 

Do you notice appreciable blow back when you take the oil filler cap off with the motor ticking over?  Mine was quite bad, and the tickover was a bit lumpy.

Hopefully yours isn't such a big deal, but on such a nicely done motor, I'd park it up and not drive till sorted. 

On the plug tracking - wait till evening, when the light is fading.  Pull the bonnet and spay the head gently witha little hand sprayer (like a windolene bottle).  It's just enough moisture to show anything wong really well.  Start her up, and if there is a tracking problem, you'll see a lightning storm till the heat clears it. 

Good luck......