Rod knock

[Carlton]

Hi all. I think my engine may be suffering with rod knock. The oil pressure on hot tickover is around 10psi but rises well at higher rpm and there is a knocking noise, which is worse at low rpm and not noticeable at normal driving speeds. I've asked my local mechanic to drop the sump and take a look at the bearings but he thinks I'm wasting my money, as the crankshaft is more than likely already damaged. His advice is to run the engine for a while longer and then get it rebuilt. My question is, should I take his advice or get the bearings checked in the hope that the crankshaft isn't yet damaged. Apart from this, the engine runs well and doesn't use any oil. It is the original TV8 with 60k on the clock (rebuilt 10k ago in 1998). The oil pump was replaced last year. Any advice would be appreciated.

[wilf]

If a big end bearing has gone to the point of knocking, you may find cutting open the oil filter (or simply looking at it if you have the original style type) may give you a clue - bearing shell material can be caught there.

Easy and cheap to do.

The cranks were hardened, if you are very (very) lucky the crank might be serviceable, I wouldn't run it any longer. But if the engine has a high mileage, then the crank may well be shot anyway.

In any case, I wouldn't run an engine with a bottom end knock any longer than I had to, to save components for reconditioning.

[Carlton]

Thanks Wilf. My mechanic also suggested looking at the oil filter. She's due an oil change anyway, so I'll do that.

[marshman]

Thanks Wilf. My mechanic also suggested looking at the oil filter. She's due an oil change anyway, so I'll do that.

When you drain the oil strain it and look at the bits - will be just as informative as looking in the oil filter. If the big ends are knocking then they won't last that long anyway and the more you drive it the more damage you may do to the crank. It is possible when it was rebuilt that the crank was reground but not hardened. In that case it may well only last 10k miles before wearing.

You say the oil pressure rises but what to?

Is your car an auto or a manual? You can tell quite a lot about what is knocking by how it responds to engine load and engine revs - harder to analyse in an auto.

Roger

[Carlton]

Thanks Roger. She's an auto and when hot, oil pressure rises to around 35psi at about 2500rpm.

[Motorsport Micky]

I'm always suspicious about an engine knock, is it from the big ends ? or maybe from the small ends of the rods ? If it's the small ends they often knock when first the engine is started (oil drainback) and the knock then disappears under normal driving, and they can last many thousand miles like this without causing engine damage.

Drop the sump...now. I'd never make a definitive statement about bearing wear or not based upon inside of oil filter, let the dog see the rabbit and make the judgement when you can see the crank. Unless the crank is really badly marked (take photos and post here) you could even just replace like for like mains and big end bearings and carry on using the car.

Micky

[Carlton]

Thanks for your advice Micky. If I go ahead and get the sump dropped, I'll try and get some photos.

[StagManiac]

Good luck with it.

Paul

[Carlton]

Thanks Paul.

[jakesmig]

With a tickover pressure of 10 psi and normal hot running at 35psi I wouldn't have been suspecting big end or mains to be overly worn, these aren't great pressures but they're certainly not catastrophic. Strange that the noise disappears as revs rise, it doesn't seem to me that the noise may be oil pressure related, I'd go looking elsewhere before stripping down the bottom end. Bear in mind, whilst I've been building engines for 45 years, i'm not a trained mechanic so what would i know.

John

[Carlton]

Thanks for your advice John. Coincidentally, my mechanic isn't convinced that the noise is oil pressure related. The only reason I'm questioning his advice is that despite being a very experienced mechanic, he hasn't worked on Stag engines before.

[Bandit1200]

I have a vague recollection that over advanced ignition timing can cause knocking.
If for no other reason that it will cost you nothing, check your timing.

Best wishes
Steve

[Carlton]

Thanks Steve. I will certainly check the timing.

[marshman]

I have a vague recollection that over advanced ignition timing can cause knocking.
If for no other reason that it will cost you nothing, check your timing.

Best wishes
Steve

It can, it's called "pinking" among other things, but I would describe it more as a deep rattle at lowish revs under heavy load (hard acceleration).

Roger

[Bandit1200]

It can, it's called "pinking" among other things, but I would describe it more as a deep rattle at lowish revs under heavy load (hard acceleration).

Roger

You are correct Roger, "pinking" or pre-ignition is one man's deep rattle or another man's knocking.

Steve