Rover V8 Sounds Like a 'Rattle Gun' Under Load

Hi Ian,

For a long time it DID sound like pinging! I was almost certain it was a dizzy problem, and i spent ages trying different timing settings and even swapped in a spare dizzy. It would sound the same on LPG and 98 RON petrol. Hard to chase the problem because every trip it would sound different!

Apart from the noise under heavy load the motor ran smoothly! A compression check showed all cylinders were around 180 psi. The noise has got worse lately though (as audible in the video) and a compression test last night told a new story!

Cyl 1 - 150 ...... Cyl 2 - 180
Cyl 3 - 190 ...... Cyl 4 - 150
Cyl 5 - 190 ...... Cyl 6 - 130
Cyl 7 - 170 ...... Cyl 8 - 180

I can also hear a very light ticking near the heads. It sounds just like leaky exhaust manifold gaskets, but considering that i glued them up the day before it must be compression gases escaping. I guess earlier on when the compression test showed good results they were not leaking badly enough (only under heavy load), but they are now leaking at idle. Interesting that the oil is clean as a whistle and there are no bubbles in the cooling system. Mustn't be leaking into these areas.

Edward :)

Hi all,

This issue is starting to test my patience... I replaced the head gaskets over the weekend and installed some refreshed 3.5 L heads (slightly lower compression than my previous 3.9L heads). Piston # 6 looked cleaner than the rest. The others had some carbon build up, but # 6 was a tan colour with very minimal carbon. I assumed water may have been leaking in and gave it a clean. I checked the headers again for cracks/holes. I put it all back together and the noise is still there!

I have narrowed down the noise to cylinder # 6 by removing one spark plug lead at a time and driving it. When i remove lead # 6 there is no rattle sound.

I did another compression test tonight. (I tested the drivers side at least 3 times):

Dry Test

1 - 150 ........ 2 - 156
3 - 150 ........ 4 - 156
5 - 160 ........ 6 - 133
7 - 150 ........ 8 - 150

Wet Test (3 squirts of oil - maybe a bit too much)

1 - ........ 2 - 180 (+24)
3 - ........ 4 - 180 (+24)
5 - ........ 6 - 180 (+47)
7 - ........ 8 - 185 (+35)

What do these results suggest? Broken ring in cylinder # 6? I can barely feel any blowby out of the oil filler, and the motor doesn't really use any oil or blow smoke. The motor only has 60,000 km on it and uses Hastings chromoly rings. Could the lower compression in cylinder 6 be from the piston being free of carbon?

Many thanks,

Edward

If it was a P76 engine I'd say it was 99.9% certain a cracked piston skirt. Not sure if Rover pistons are prone to do the same. P76 pistons used to crack down one or both sides of one skirt and rattle under load, if you drove it long enough the skirt would fall off and the oil ring no longer work. Still drove though. With the head off you'd have a lot of piston rock compared with an adjacent one.

Thanks Beeutey. I guess i won't know for sure until i pull it out.

The pistons are new + 20 thou oversize 9.35:1 pistons. Can't remember the brand, but they were recommended by the engine builder who bored out the cylinders.

Edward

Nobody seems to have suggested that a sleeve is loose and bouncing up and down.
It is less likely on a 3.5 than a 3.9 but is not unknown.
it is caused by the block cracking behind the sleeve and the sleeve losing interference tension.
I recall that Graeme Cooper once told me he stopped doing stroker kits on 3.5s because they invariably caused a sleeve to fail.
I hope it is a cracked piston , but the most likely explanation is a loose sleeve .
The loose sleeves generally only happen on the middle 2 cylinders.
Regards PhilipA

Thanks PhilipA for that information that I didn’t want to hear :p

I won’t discount that as a possible issue. I did check the deck heights and all the bores appeared flush. I also did not see any cracks around the cylinder casting. From my research a slipped liner is more likely to occur when the motor comes up to operating temp, but this rattle gets BETTER when the motor warms up. For example, it rattled today in 2^nd gear at low load, but as the motor warmed up it only rattled under heavy load in 3^rd and 4^th.

What I did see was a bit of a polished spot on the bore in cylinder # 6 though, where the hone marks were more difficult to see. About the sizer of a 5 or 10 c piece. I’m pretty sure it was on cylinder 6…

Edward

Quote:

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I also did not see any cracks around the cylinder casting.

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The cracks happen about 2-3 inches down the block behind the sleeve.
Regards PhilipA

If it were a 3.9, 4.0 or 4.6 I would say a slipped liner on number 6 - the steam cleaning of the piston and the noise would be the clue.

However, while not unheard off, doesn't seem to happen much on the 3.5.

Other than the obove comment I am not able to actually offer a solution as you have honed into the problem area - maybe run the engine with no 6 spark plug lead disconnected and see if you have green coolant in the cylinder (would need a borescope).

Garry

Quote:

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but # 6 was a tan colour with very minimal carbon. I assumed water may have been leaking in and gave it a clean

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This is an additional clue that you may have a slipped sleeve which I just remembered.

There are no connecting waterways in a RV8 except at the extreme rear or front of the heads.

For water to be present in a bore it must be a cracked head or cracked block.

A blown head gasket will not cause water to be in number 6.

Look it is very difficult to diagnose from afar but this is a relatively common thing in 3.9 upwards but not so much in 3.5 as the supporting alloy structure in a 3.5 is thicker. However the block castings were never that accurate .

Regards PhilipA

The other thing is that a slipped liner only tends to clack away when the engine is cooler and as it heats up and expands it then locks in - so noise under load as originally described is not typical - as Philip said hard to diagnose from afar.

I must admit on reading the very first post the symptom seemed to be typical pinging - either caused by advanced timing, or low octane fuel, or lean burning or other ignition sources such as carbon in the engine.

Then as further symptoms were revealed I started to think slipped liner due to the steam cleaning of a piston - number 6 cylinder obvious has an issue but 3.5s tend not to slip liners.

At this stage I have no idea - did you put lifter lubricant in the oil just in case the noise was a sticky lifter?

Good luck

Garry