Fault Diagnosis - Compression loss, oil usage and popping

[kritip]

Firstly, I apologise if I break any rules, I have read them all and respect this sites' professional nature and the wealth of knowledge contained within.

I am looking for any ideas or advice on my engine problem.

The engine is a:

1368cc 16V Fiat engine, ala Stilo, Punto mk3, Idea, Panda 100HP.

It is similar in design and construction to 1242 16V Fiat units, but with a slightly larger bore and stroke.


Since I installed it into my Seicento, taken from a rear ended 8K Panda 100hp, it seems to have used a fair bit of oil, and has got progressively worse.

I recently did a compression test, the results are attached.

It now seems to also be popping in the inlet slightly, blowing smoke on startup and high rpm and rattling at high rpm.


Does anyone with experience of these have any ideas where/what could be wrong. The engine now has about 18K on it.

To me, the compression results ALL seem low, especially cylinder one. I did the test fully warmed up, wide open throttle, and all the plugs out.

I presume I will have to pull the head for further diagnosis, but ideas of what to look at/for would be appreciated.

If the head or pistons need work, would it be best to go to a specialist like GC? Or for a stock engine, should any rebuilder be able to sort it out?

Thank you very much for any help.

Kristian

[kritip]

Hello again.

I started to strip the top end down yesterday. As I was doing so I found oil in the intake, oil sitting on top of the closed valves that had run down.

I then removed the head, and on all of the pistons, was oil.

The valves looked ok visually, but after the head was off I had to call it a night.

This afternoon, I set about removing the pistons. I have only done one so far, but it doesn't look good.

I have attached pictures of piston number one. Is this classic detonation?

P1020209.JPG (98.87 KiB) Viewed 6134 times

P1020205.JPG (151.91 KiB) Viewed 6131 times

P1020203.JPG (124.04 KiB) Viewed 6132 times

P1020202.JPG (106.21 KiB) Viewed 6129 times

thank you,

Kristian

[Guy Croft]

Yes it is, well done for a good diagnostic strip, classic detonation symptoms - disruption of the alloy around the edge of the crown and - especially - cracked land caused by the sudden violent pressure rise during det event (up to 20 times peak cylinder pressure) with associated high temp.

GC

[kritip]

Thank you very much Guy!

Is this the only place I would expect to see damage, or should I strip the valves etc. They all look visually fine.

I am ordering four more pistons direct from Fiat, as I can't source them from anywhere else, unless you can supply them or an alternative? I will then getting the block checked and bored if needed.

I am confused about pistons though. Mine are Class A, and looking at the Fiat catalouge, you can get Class A, B or C. What is the difference? Are they different diameters? They also do an oversize of 0.1 in each class as well.

Most importantly I have to find the cause of the problem...could have been user error, as I am running megasquirt, or it could have been started before I got the engine, as it was from a scrap yard. I only ran a max advance of 30 degrees, and always kept AFR's on the richer side.

Regards,

Kristian

[Guy Croft]

After a major event like that the engine must have a full strip, you cannt assume the damage is confined to the pistons. It might have been caused by fuel octane too low, plugs too hot, over-hot engine and thus too-high intake air temperature. There are many possible causes, try a search under detonation, I have written extensively on this site. Sometimes you never find the cause but overheating on hot days (100deg C plus engine temp) is the most common.

You need to look for bearing overload damage, debris damage in the oil pump. The head and block must be at least cheacked for flatness and it's common in that situation to have damage around the fire ring and squish regions of the head. The valves need to be take out and checked for distortion and you might have some distortion on the seat inserts too - usually inlet side. I recently did a Tipo 16v that had suffered chronic detonation and all the inlet seat inserts had gone oval and pulled away from the surrounding alloy.

I only supply GC designed competition/forged pistons now, I stopped handling OE rods and pistons some years back.

For info on bore sizes and classes read the article in the GC Virtual Workshop at:

viewtopic.php?f=3&t=254

Naturally, after rebuild, you would be well-advised to examine every aspect of octane, fuelling, ignition, cooling & temperatures etc before running again, you don't want to be rebuilding twice..

Hope this helps,

GC

[kritip]

Thank you very much again Guy.

I will strip down the head then, the oil pump is being replaced anyway, and I will make sure the enigne temps are fine etc. I think I will also run on 97/98 RON as, although its a bit more expensive at the pump, it will be wort it in the long run.

I have also taken the oportunity to get my cams reground, may as well while I'm going this far.

Shame about the pistons, they will be out of my price range I'm afraid. £380 for rings and pistons from the dealer it is then.

I did do a search about detonation, and pisotns but missed the link you posted :)

Thanks again for your time. I'll post up once it's all back and running :)

Regards,

Kristian

[Guy Croft]

By the way (not knowing which came first - det or oil consumption) it is worth mentioning that oil contamination of the charge (drawn past the rings on the intake stroke and via guides on low throttle when there is manifold vacuum) is known to cause (or more correctly perhaps said to cause..) detonation.

But - I have experimented with this, you need a fair bit of oil...



G