Hello all.

Hoping I can get some help with a question.

A 2002 Stype. 8cylinder. Compression o this entire bank is nothing above 50psi??? Crazy. Took cam cover of, turned engine, flats line up, this first cylinder at TDC, Cams are off the tappets, and valves are UP.
So, what else could be the cause of low compression? I've dropped an oz of oil into the cylinders (a buddy swore a mix of gas and tranny oil was a better bet - I disagreed) and still. 20, 28, 46 and 48 lbs in each, respectively, front to back.

What's happening?

 

Do you have the timing mark in the flywheel aligned?
The flats should not be aligned at TDC IIRC it's 45deg before.

 

I can't see clearly but looks to have the BAD tensioners (discoloured, orange-ish plastic). If so, get 'em changed! (plus the guides etc)

 

THE ENGINE IS NOT TIMED AT TDC!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!

Please get familiarized with the timing setup before going any farther!!!!!!!!!!!!!!!!!!!!!!
(All crank/cam timing is done at 45 degrees AFTER TDC)

I uploaded my copy of V8/V6 engine repair course 168 to the internet and it is available with a search.

bob

bob

 

so... ive done some work on these engines before. change A and B heads on my xk8...

i know that it needs a tensioner upgrade - upper, seconds and guides. thanks...

i think people are getting caught up at the TDC idea and not addressing the real question of and reason for the post. ok,,, the engine is NOT at top dead center (as I wrongly stated) but the cams are aligned, timed, no? the flats line up. timing looks correct... at first i was inspecting to see (this is my first look) if it had jumped a tooth or two (was afraid more since compression was so low) and bent valves. that does not seem to be the case. the s type is an interference engine, correct?

in the photo you can see - and yes - on the RH (pass) side of the motor, while that first cylinder is at the max height of its travel (tho not at TDC), both valves are completely closed and the lobes are off the taps - which makes sense.

my question is,,, what MIGHT be causing the looow compression, in all of you's experience?

 

So what's the history? has to be a story.

The flats may be aligned but are they aligned in the right place?

 

I'm helping someone that doesn't know much about the car other than they like to drive it. They asked me to help because the car stopped running in March...

I tested for compression and it was low. There is fuel, spark but no compression - or very low. I removed the cover to see what I could see, expecting a timing issue. There doesn't seem to be one. So, at that point I can to the forum, which I have been using for two + years to ask for some help.

What's "aligned in the right place" mean?

 

Is the timing mark on the flywheel aligned at the same time as the flats on the camshafts?
Is it just one bank with no compression? Are the flats on the other bank aligned at the same time?

 

If it already jumped timing... what would compression be...

One tooth - maybe no damage. Any more and it's an interference engine...

 

You might be suffering from BORE-WASH.

Nikasil engines use very lightly sprung piston rings. The bore can lose the thin oil coating and the rings need that oil to seal.

bob

 

Im sorry to say that i havent gone so deeply into it, yet... For now, i am where i am. What im looking at and what i jave offered is all i got. More info will be forthcoming since what i have so far clearly isnt enough to produce suggestions or guidance. Thanks folks

 

I am with Bob on this one. Could be the damage of the nikasil coating, fouled up rings, lubrication issue or even an fuel (ratio) issue. Was the oil okay? And oil level? Did you check comp on the other bank too? Any error codes (o2, injector or coil related)?

 

Well a 2002 would NOT have the Nikasil problem.
BUT bore wash is a good guess. Still the added engine oil when doing the compression test should have helped that a lot.

Are you sure it has not jumped time?
.
.
.

 

true, the 4.2 does not have that issue, but looking att the tensioners and the intake I guesed it would be a 4.0 :-)

Jay: is it a '02 model or actually a '01?

 

No the later 4.0L V-8's stopped using Nikasil too.
We had a cut off date somewhere in the 1999-2000 date range. So the 2002 year is AFTER the entire Nikasil problems.
.
.
.

 

Just to be clear about the Nikasil problem.
The first 4.0 V8 engine with steel liners was made at 10:43am on August 18th 2000. (First day back after the summer holiday shut down.)
It has engine number 0008181043 (00 year, 08 month, 18 date, 10:43 time.)
So, any engine before this number has the Nikasil coating and any engine after this number has the steel bore liners.

 

Yes, and you can't rely on the car's date to say which engine it has - other than (say) a 2003 won't have one. (It'll have the 4.2 anyway instead of 4.0 but you get the idea - check the actual engine #)

By now nikasil does not seem to be a problem - I suppose because if it were then the engine would already be toast.

What is a problem? The use of plastic-bodied tensioners for the timing chain. Need to be the metal kind.

 

Hello all. Thanks for the thoughtful posts. Its been rain here so not a lot to add or update.

Im pretty sure it's an 02. I know there are cut off dates which actually determine the way year appears in titles. I have not checked the compression on the opposite bank. The oil is fine. And, an once or more was dropped into each cylinder on cranking. Fuel ratio shouldn't effect the compression as uniformly - I don't think.

I have some digging to do. Maybe a bad compression reader!? Still, she will not start. I haven't spent a lot of time with her,,, and the guy that has ain't so swift. His jabbrring might have sent me looking i the wrong direction all together .

I think I am past nikisil by model year. If not,,, all four cylinders,,, all four ring sets? Sounds like too much a coincidence.

where are my sunny skys?

 

Just to make sure, did you check compression with wide opened throttle? That's a must to get the correct reference values.

If the throttle is in idle position just cracked open a few degrees for the measurement, the cylinder starts compression at a very low pressure level, therefore also only reaching a low peak pressure level comparable to what you present.

 

Aix...!

Super good point! No I did not! But Will!

Thank you for that, much appreciated!