Knocking engine and burning oil when hot

maxgreenwood · Post by **maxgreenwood** » Tue Sep 20, 2011 12:23 am

I have mentioned my noisy engine here already and the garage said it was 'crankshaft rumble' and not to worry about it, but now i'm not so sure they heard the extent of the noise when engine is fully warmed up.

I'm talking about a 16 carb petrol. 1990 TZS

I've got blue smoke out the exhaust on acceleration, not idle, which is accompanied with knocking, but only at a particular medium load, full throttle it goes.. And the blue smoke and knocking only occur when engine is fully warmed up. It sounds pretty sweet before then and no fumes.

It seems to be getting slowly worse. The engine is using oil. And the other day i took off the oil filler cap whilst engine running at full operating temp. , and there is what looks like the same blue fumes coming out of the oil filler pipe too, which was quite alarming and is making me think this could be more serious than 1st anticipated.

The timing and fueling has been set by the garage and seems spot on.

The cambelt was done a few months ago.

I have just done an oil and filter change to see what that would do, using 15w 40, before that i had 10w 40 - no discernable difference.

It did run low on oil (before i knew it was using it) on a run, with me up to 4000 rpm at times. But there was still a few mm oil on the bottom of the dipstick.

The knocking only showed up once i'd replaced the vacuum advance capsule. The timing was previously advanced about 10mm from it's current correct position when i got the car (and the vacuum advance wasn't working, but connected)

I don't have any mechanical background when it comes to cars but i've come to understand all this technical stuff in trying to get the car sorted.

From searching the web etc, could it be piston rings?

Willy · Post by **Willy** » Tue Sep 20, 2011 1:03 am

Piston rings problems could probably explain your blue smoke problem, that's oil being burnt. It probably becomes more apparent when the engine's warm as the oil is fluid enough to leak up the cylinders. That could also explain your "smoke in the oil", high pressure + hot air leaking out at TDC.

Check your sparks plugs, that should help diagnose if it's just one cylinder or more (Haynes has diagnoses in the back for these). If it's just one and the piston is seriously damaged, then that could explain the knocking, as the engine could be giving uneven torque fluctuations.

But there was still a few mm oil on the bottom of the dipstick

The difference between high and low on a dipstick is still a good litre, remember.

If you've adjusted the vacuum advance, try adjusting it back? It may sound elementary, but hopefully your knocking will just be ignition a few degrees too early (causes large engine stresses if you're firing early, but it's a very simple fix).

Will

maxgreenwood · Post by **maxgreenwood** » Tue Sep 20, 2011 1:19 am

Thanks Willy,
the timing has been set by the garage with the new vac advance caps on so i'm reluctant to change it. i should take it down there and listen with them and talk it over.

Maybe if it had been advanced to compensate for lack of vacuum advance at somepoint before i got the car, this might have put stress on the engine leading to this wear, but i'm not sure how that would affect it. It didn't seem to be knocking at that stage. It will be a real shame if this becomes a big problem as i've had some big jobs done and i really like the car.

I'll check the spark plugs, i fitted new ones around 3k ago.

It's very smelly, petrol/oily as well as smoky at the moment.

citronut · Post by **citronut** » Tue Sep 20, 2011 8:24 am

if the knocking was not there before re/timming after the advance capsule was fitted, it is almost certainly a timming issue causeing it,

the smoke could be a blocked crank case breather, which will presureise the sump,

did you oil warning lamp light when low on oil, if not then the oil pump was still finding oil, as the warning lamp lights when there is no or very low oil presure,

if it did not light then its unlikely this caused any damage,

regards malcolm

maxgreenwood · Post by **maxgreenwood** » Tue Sep 20, 2011 9:13 am

Hi Malcolm,
the light did not come on.
where is the crank case breather? How would you unblock?

I trust the garage with the timing setup, and i experimented with it myself beforehand. I think this knocking is different from the knocking obtained by too much advance.

I'll take it back to the garage so they can have a quick look i think.

Post by **mat_fenwick** » Tue Sep 20, 2011 9:53 am

Pinking from too much ignition advance is more of a 'tinkling' sound, so that seems less likely to me. Perhaps another Youtube video? Do you know any good sound engineers?

The crankcase breather system is designed to take any pressureisation of the crankcase (from any combustion gases leaking past the piston rings) away as otherwise the pressure build up would damage seals and cause oil leaks. All engines will leak past the rings slightly but obviously more so with a worn engine. In the past this was vented to atmosphere but for the last 30-40 years it is now drawn into the air intake system and burnt. There should be a pipe from the oil filler to the air filter somewhere - if you pull that off at the air filter end and you still see as much smoke that proves the breather system is OK.

To me, the oil consumption/smoke from the filler does sound like worn bores/rings. A compression tester is pretty cheap to buy and as easy to use as changing spark plugs - that will give you a good idea of where the problem is.

Gibbo2286 · Post by **Gibbo2286** » Tue Sep 20, 2011 10:33 am

Your description of the knocking says to me big end bearing and I'd recommend that you have it investigated further before you have what we in the trade call a 'leg out of bed' i.e. a broken con rod through the side of the crankcase.

You might get away with a set of big end shells if you're very lucky and have caught it in time before too much damage has been done to the crankshaft although that's a rare occurence.

Post by **mat_fenwick** » Tue Sep 20, 2011 11:16 am

/\ I thought that as well, but the bit about going away under load puzzled me. I've not heard a big end knock personally (although heard knocking that may or may not have been, just not diagnosed for certain) so I'm not confident enough to make a diagnosis on it.

The other point to note is that a 10w40 and a 15w40 have nominally the same viscosity when hot so wouldn't expect a difference if the noise is oil pressure related. I think that the recommended range goes right up to a 20w50, but I'm not recommending just putting a thicker oil in to hide the problem.

maxgreenwood · Post by **maxgreenwood** » Tue Sep 20, 2011 11:40 am

Thanks for all your thoughts here.

I just took it down the garage. It doesn't look good. Probably piston rings. "I'd start rooting around for another car" was their advice.

The knocking he said was the crankshaft, not sure if that means the bearings or what. But more importantly the engine would need an overhaul, head and sump off. Big job. €1500.

The car really smells and it is now embarrising covering following cars in clouds of dirty blue smoke.

This is really annoying, but a lesson learned with a car i bought in February more with my heart than head. I've driven it for 6000 miles in that time.

I have had the clutch and cambelt and the big octopus done in the last 6 months. That's a load of money i needn't have spent. Also spheres and re-con struts, but i can transfer them to another one.

I might be able to tackle the job myself with some help and a garage somewhere, but not for a while.

I'd better start looking for some more wheels.

KevR · Post by **KevR** » Tue Sep 20, 2011 11:50 am

maxgreenwood wrote:
I'd better start looking for some more wheels.

I'd be more inclined to look around for a secondhand engine.

maxgreenwood · Post by **maxgreenwood** » Tue Sep 20, 2011 11:58 am

that is an option, although i don't know how i'd do it. Maybe i could fit a GTi engine and put the speedlines on it looks like i've aquired.

Philip Chidlow · Post by **Philip Chidlow** » Tue Sep 20, 2011 12:11 pm

Could do a lot worse than fit a GTi engine: everything else - is pretty much the same.

sdelasal · Post by **sdelasal** » Tue Sep 20, 2011 12:26 pm

Max - sounds like you need a trip to essex and a nice 1993 TXD diesel estate - in Red

Willy · Post by **Willy** » Tue Sep 20, 2011 12:37 pm

Root around on ebay/here for a second hand engine/someone breaking their car. Money-wise, you'd probably be better off splicing in a replacement - maybe even a cheap bare one if all your auxillaries are in good shape. It could possibly work out cheaper than breaking your car for pittence or spend E1500 on getting it fixed. Try a diesel

maxgreenwood · Post by **maxgreenwood** » Tue Sep 20, 2011 1:29 pm

used to have a diesel, a good TZD turbo estate. Sold it 2 years ago

Max - sounds like you need a trip to essex and a nice 1993 TXD diesel estate - in Red Wink

I have been looking around for an XM estate, the BX is great round town, but a big mile muncher would be great for work trips round the country and family holidays. If i can i might move on this more quickly and repair the BX as and when. I have had a generous offer of help from a club member with respect to engine swapping, so I am officially on the look out for a good replacement.