Zero compression on a Saxo

Unread post by **CitroJim** » 31 May 2008, 14:04

A neighbours son's Saxo arrived home this morning on the back of an AA wagon

As sure as night turns into day, it was not long before I was called in to cast a thought or two

The engine has what appeared the usual TU oil leak and signs of explosive coolant loss, but not much.. It still has coolant in it and it's clean.

The engine spins over with no compression at all. Cambelt I though but that is intact. The cam is rotating and valves are operating.

A compression test shows absolute zero on Cylinders 2, 3 and 4. I did not bother to test No.1. On how it sounds, No.1 is unlikely to have any compression either.

The owner, 17 years old, just got the car yesterday, just passed his test said all he heard was a rattle, a loss of power and then it died..

His dad is lifting the head this weekend.

Any thoughts on what has happened to loose compression totally on at least three cylinders? My only thought is destructive detonation and holed pistons or badly burned valves. The plugs are sparkly clean with no combustion products on them whatsoever. But why all four cylinders?

It's a TU1 engine.

deian · Unread post by **deian** » 31 May 2008, 14:11

Zero compression would point to destroyed piston rings. or a the pistons have dissappeared down a black hole (right??).

Surely it would show some kind of compression (even very very low nubers) even if there is some kind of hole for the air to escape to.

In saying that, could the valves be stuck open (i.e broken camshaft, bearings on the geared pulleys welded into place etc... would point to a broken camblet.

Anyway, it doesn't sound good at all!

slim123 · Unread post by **slim123** » 31 May 2008, 14:29

Hi Jim.

Just a thought but in the past I have known these little TU engines to strip a few teeth on the cambelt, looking at it all appears normal and sometimes even the camshaft will turn, albeit now out of time!

Over revving can also cause a valve bounce on these engines, 17 years old, just passed the test, driving a Saxo? Quite possible!

Who owned it last, there are a lot of 17 year old "race mechanics" out there who seen to think that they can make a Saxo very fast and furious, maybe the problem is simply a poorly done head job.

I would be very surprised if it was rings as one compression maybe but not on all 4 at the same time.

Thats about all I can think of.

Regards
Slim.

AndersDK · Unread post by **AndersDK** » 31 May 2008, 15:23

Timing belt has slipped. Valves out of timing may produce these highly "unlikely" readings on a comp test.

Its a head off job, as there will be bent valves as well.

A friendly debriefing of the driver may reveal if the engine was mistreated, but it is likely that a loose fit belt can do exactly this.

citronut · Unread post by **citronut** » 31 May 2008, 16:22

im with Slim and Anders on this one, a few teath stripped, so it is sill allowing the cam to rotate openning more valves, i feel sure all 25 HE HE HE will be bent,

i have seen this sort of thing before

if it were rings you would get some compresion
regards malcolm

Unread post by **CitroJim** » 31 May 2008, 17:44

Thanks all, I reckon the belt jump/tooth loss is the one although on the bit of the belt I can see, I cannot see anything the matter and it's under good tension although both the belt and tensioner look ancient.

Could valve bounce cause the timing to jump?

His dad is getting on well, he has the exhaust manifold off and the inlet is shortly to come off. Those little 8V TU engines are a joy to work on compared to an XU(D). So much space, such a tiny engine

His dad also told me, in confidence, he has lectured him several times about thrashing it

lesson learned...

AndersDK · Unread post by **AndersDK** » 31 May 2008, 18:30

Valve bounce ????

Never heard of it - except that valves may tend to stick partly open because of too much friction in their guides at hi revs. But I cant see how that would influence the cambelt - unless the cam itself gets locked.

Either this engine has truly been trashed - or the cambelt history is not true.

MikeT · Unread post by **MikeT** » 31 May 2008, 19:40

Sorry to butt in, I don't really have anything worthwhile to add but the info so far has left me with some questions.

Is the compression tester confirmed working? Did you confirm the pistons and valves are actually moving on cranking?

Unread post by **CitroJim** » 31 May 2008, 19:51

MikeT wrote: Is the compression tester confirmed working? Did you confirm the pistons and valves are actually moving on cranking?

No, the compression tester is fine Mike. When I said zero, No.3 did give about 20 psi (a kick of the needle). No. 4 and 2 really were zero though.

The valves move. The starter motor sounds like its doing no work to speak of when it [literally] spins the engine. It was going wheeee rather than ruurr, hurr, hurr, hurr

MikeT · Unread post by **MikeT** » 31 May 2008, 20:03

That eliminates the crank end then

Not much help now but you can tell a lot about the state of a working engine as well as the fuelling from the plugs. Lots of "pepper" or diamonds indicates freerange metal.

deian · Unread post by **deian** » 31 May 2008, 20:42

citrojim wrote:t was going wheeee rather than ruurr, hurr, hurr, hurr

gotta love the sound effects

i agree, my theories were a bit unreal and illogical

...but i wouldn't be surprised if the engine was thrashed to bits... being a 17yr old in the 'saxo', which have a certain reputation in that age group. I refuse to buy one based on the image it's had. I would however buy a clean unmodified VTS (aguy who works with me reckons he's trained peugeot mechanic and swears the VTR is faster than the VTS, I however know better).

so yes, i think the engine has been a victim of a boy racer and sounds like it needs some expensive work.

Unread post by **CitroJim** » 01 Jun 2008, 21:26

The head is off.

Timing had not slipped, no teeth off the belt, no bent valves but..

A big hole in No.1 piston and all four exhaust valves with chunks out of them. Lots of fine specks of metal around the other piston crowns.

Looks like a case of severe detonation (pinking) hence the rattling noise the driver heard.

When the airbox was being removed, it was noted that the pipe leading from the inlet manifold to the breather was broken at its joint, thus allowing rather a lot of air to bleed into the inlet manifold and causing a very weak mixture. That would seem to explain the reason for the destructive detonation.

The search is on for a replacement engine complete.

AndersDK · Unread post by **AndersDK** » 01 Jun 2008, 22:16

A rather surprising explanation ...

Symptoms like - and indications on - a trashed engine - but the driver is innocent

Unread post by **CitroJim** » 01 Jun 2008, 22:19

AndersDK wrote: Symptoms like - and indications on - a trashed engine - but the driver is innocent

Indeed. His dad and I spent some time this evening gently convincing him it was not his fault

slim123 · Unread post by **slim123** » 01 Jun 2008, 22:40

Must have been detonating for a long time before destruction, these things usualy take a while to destroy an engine.

My guess is after having a couple of 17 year old drivers, is that the music volume disguised the detonation noise for a while!!!!

Still at least an engine should be easy to find and cheap enough.

Regards
Slim.