Crank Rumble. V8S

[trackcar]

One for V8 Racing maybe :

My V8S has started to rumble on warm start-up. It sounds just like an old Triumph straight 6 start-up crank rumble ..

however: from cold start there is no rumble at all, it only occurs when the car has done a fair run, is well up to temperature and i leave the car for an hour or so before restarting .. the rumble is there for maybe 3 seconds and then all is quiet once more.

Curiously the oil pressure follows exactly the same patterns it always has, never makes less than 30psi on my gauge which is what it's always done at hot cruise. At tickover it's around 25psi on the gause. The pressure builds up on the gauge just as slowly as it always has (tho of course the gauge is bi-metallic heated element so not exactly the most sprightly gauge at the best of times).

Wonder if anyone has come across this before .. it *sounds* like crank rumble but maybe it isn't? I was thinking maybe the oil pump isn't pressuring very well on hot thin oil start, but that's the only thing i could think of.

thanks in advance for any information



>> Edited by trackcar on Thursday 8th December 08:06

[GreenV8S]

Time for some plastigauge, maybe?

[HarryW]

I assume the same noise is apparent with clutch dipped or not . Mine was completly stripped at around 90K and funnily enough the bottom end was fine, just a polish, re-shell and hone required, whether that was due to being fully balanced or not I'm not sure.
I'm sure Rob will be able to say what the normal prognosis is. Apart from excessive revs or oil surge on fast corners the 4ltr afaik has a fairly sound bottom end. Could just as easily and more commonly be cam bearings .
Then again what the feck do I know .

Harry

[trackcar]

GreenV8S said:

Time for some plastigauge, maybe?

yeah that should thicken the oil up nicely

[GreenV8S]

trackcar said:

GreenV8S said: Time for some plastigauge, maybe? yeah that should thicken the oil up nicely

[v8 racing]

Ep 90 works quite well in these situations! to be honest i am a little stumped, i doubt very much it will be bearing issue problems if it doesnt do it from cold, the followers arent bleeding down are they? but this would also cause them to rattle when cold i would have thought? it must be something to do with a component that expands with heat and stays expanded, rocker arms??

[trackcar]

It's something much heavier than that Rob .. you can feel it through the car and it sounds just like that crank sound triumph straight sixes make when they start up.

I might pull the sump off and take a couple of caps off to see what's going on in there. might be prudent to stick a new oil pump gearset and end plate in there too .. but yeah it's got me a bit stumped aswell!

[v8 racing]

Surely if it was shells it would it from stone cold?? the gears wont be a problem these can be absolutely scrap and still produce reasonable oil pressure! i have just thought of something that happened a long time ago on the sd1's the oil filter has it got a non return valve in it ie genuine filter? if its a coopers or the like these can actually drain out back into the sump and it takes a few seconds to fill them back up?

[Boosted Ls1]

Has it had a thrashing recently? It does sound like a clearance issue once warm but is s deep sound. So, I'd wonder about thinning oil, past it's sell by date or a piston bore issue which sometimes sounds like a bottom end problem.

Boosted.