Engine woes

[Teetertank]

Have never been totally happy with the idling on ’97 Chimaera 500, and last weekend carried out a compression test.

The readings were (in Psi):

85
87
87
90
92
87
85

…so all very consistent, but worryingly low. From research on this site and elsewhere on the net I would hope for readings or around 170PSI so seems my compression figures are all about half of what is considered healthy.

What started the investigation was a low inlet manifold vacuum reading which was 12.5” Hg and would expect it to be around 20 – 25, but have not been able to verify this with any other TVR engines, but when compared to a similar Range Rover engine, was low compared to the Range’s 20”Hg reading.

Idling seems a little lumpy, but not actually misfiring. Power seems good, in spite of the low compression readings, but as its my first Chim, maybe I don’t know what I’m missing performance wise.

With the low cylinder compression readings and low vacuum in the inlet, I am worried that piston rings are worn, and that the engine needs a rebuild, but mileage is only 52K and compression readings seem so consistent that I am not convinced that the piston rings would all be so consistently worn out already?

Has anybody else had similar symptoms and can anyone suggest what healthy vacuum and compression figures should be? Or can anyone help with any suggestions/cause of these figures? Thanks.

[The AJP Griff]

Please dont take this the wrong way,but did you check your compression when hot or cold?

[Teetertank]

That's a fair question Griff, and the answer is the engine was warm but probably couldn't be described as "hot".

Had been running the engine a fair bit for various investigations before the compression test was done, but not actually revving it hard.

However, even if the engine was cold, I wouldn't expect the compression figures to be down by half. Would you?

I also didn't do a wet test, which may have been revealing, and or a leak down test. But welcome any suggestions before I have the next opportunity to do any more tests.

[chrispitman]

Have you calibrated the tester against a know value.

[tvralfagtv6]

interested to see the out come on this, just to get out of the way, fullthrottle when doing compression test?, the fact they are all consistant is good ,as I have never seen a motor where 4,6 or 8 cylinders are aprox 100psi down, for info hot and cold on my cosworth was worth 15 psi,long duration cams reduce vacum at idle and copression readings,however a bd3 in said cosworth 290 duration still gave 150 psi cold.I can not believe the cam is so worn on all cylinders,has your comp tester got the little rubber o ring, shooting the breeze hope it helps, it may spark some thoughts on your side.

[lotusandy]

Just to eliminate it how exactly are you perfoming the test?
I have always removed all the spark plugs with a reasonably hot engine, and held the throttle wide open, removing all the spark plugs gives the engine a chance to spin over reasonably quickly....
Just my thoughts.

Andy

[Teetertank]

chrispitman said:

Have you calibrated the tester against a know value.

No, but have used the same gauge before with expected results, albeit a couple of years ago.

Would be worth checking it as you say, but the vacuum gauge on the inlet must be reading correctly as tested it on a Range Rover V8 on the same day.

[Teetertank]

tvralfagtv6 said:

interested to see the out come on this, just to get out of the way, fullthrottle when doing compression test?, the fact they are all consistant is good ,as I have never seen a motor where 4,6 or 8 cylinders are aprox 100psi down, for info hot and cold on my cosworth was worth 15 psi,long duration cams reduce vacum at idle and copression readings,however a bd3 in said cosworth 290 duration still gave 150 psi cold.I can not believe the cam is so worn on all cylinders,has your comp tester got the little rubber o ring, shooting the breeze hope it helps, it may spark some thoughts on your side.

Yes, throttle was held open during the test.

Your 15 psi confirms suspicion that hot engine doesn’t make as big a difference between ideal readings and what I have.

Looking through the (complete) service history, I have no reason to believe there is a hot cam fitted, so would expect “normal” readings.

Yes, the tester had an o ring

I fear that the vacuum loss ties in with worn rings, as if the cylinders are not achieving good compression figures, there would be a reduction in inlet “sucking power”.

I am hoping that there will be something simple that I have overlooked, as it is uncanny that all the readings were so consistent and yet all so low.

[Teetertank]

lotusandy said:

Just to eliminate it how exactly are you perfoming the test?
I have always removed all the spark plugs with a reasonably hot engine, and held the throttle wide open, removing all the spark plugs gives the engine a chance to spin over reasonably quickly....
Just my thoughts.

Andy

Thanks Andy.
I performed the test almost exactly as you do, i.e. removed all spark plugs, and throttle held open during cranking. The engine had been idling for quite a while (on and off) before the test, so was warm, but not really hot.

Has no one ever had such low compression on one of these? And to add insult to injury, this is supposedly "High Compression" engine!

[The AJP Griff]

Hugo,i must admit that whilst i wouldn't know exactly what to expect when cold,those readings are pretty low.As to wheather the engine was warmed up first,was just a quick check,just in case.Do you get through a lot of oil?If they really were that worn i would expect consumption to be pretty high.The RV8 is known to suffer little boar wear,even having honong marks still present on very high mileage engines,apparently.Heres hoping for you it's just the gauge your using.

[Teetertank]

The AJP Griff said:

Hugo,i must admit that whilst i wouldn't know exactly what to expect when cold,those readings are pretty low.As to wheather the engine was warmed up first,was just a quick check,just in case.Do you get through a lot of oil?If they really were that worn i would expect consumption to be pretty high.The RV8 is known to suffer little boar wear,even having honong marks still present on very high mileage engines,apparently.Heres hoping for you it's just the gauge your using.

Thanks Andy,

I have only had the car for just under one month. The first thing I did was change all the fluids, and gave it a complete service, including new plugs, dizzy cap & arm. New leads are on order as is a new coil (these were in the hope it may sort the rough idle).

As for oil consumption, it is still early days to really tell. but I have done about 300 miles since changing the oil and I would say the level is down maybe one fifth to one quarter of the way from the high mark. So would say yes it has used some, but from reading consumption figures here and in the bible, this doesn't seem alarming (although I read enviously, that others here suffer no oil loss whatsoever). For the record I added 6 litres when changing the oil (& filter), as the recommended 5 litres didn't bring it up to the top level.

Also the oil is still perfectly clear in the sump (after 300 miles) and was pleasantly surprised by the colour of the engine oil I drained out when changing - it wasn't clear, but not sludgy at all, and there was a hint of a light-ish colour still there. If the pistons were worn, wouldn't you expect the oil to be black by now?

Boy, I really hope it is a faulty gauge, but fear that's not the case, and major works are imminent.

[paulathome]

Have you done another compression test after squirting a drop of oil into each cylinder.
If the compression then increases significantly then the bores/rings will be worn.
Just a thought.
Paul.

Edited by paulathome on Tuesday 7th October 19:15

[rev-erend]

paulathome said:

Have you done another compression test after squirting a drop of oil into each cylinder.
If the compression then increases significantly then the bores/rings will be worn.
Just a thought.
Paul.

Edited by paulathome on Tuesday 7th October 19:15

What he said..

[That Daddy]

Those readings are to consistant,engines dont wear that evenly,your gauge is knackered they are consistantly low and thats your gauge get a new one or get a garage to carry out a leak down test(much more accurate test of bore/piston seal)compression gauges are good for quick tests burnt valves,holed pistons etc.

Edited by That Daddy on Tuesday 7th October 21:07

[Teetertank]

I will try and get a leakdown test done at the weekend.

Can any of you think of any other reason, other than a knackered gauge, that would bring all cylinders down no compression?

I would have thought that a compression loss of 100psi should be pretty noticeable as a power loss when driving, but without having owned the car for long or had the opportunity to compare to others, I can’t say for sure how it compares to normal performance.

However the inlet manifold vacuum is still down (and that gauge was proven to be good) and haven’t been able to locate any leaks from spraying gas around any joints or listening for leaks. If there are no external leaks then the vacuum loss could be explained by potentially leaking piston rings or valves? I did get a stethoscope yesterday and will adapt it to listen for any leaks, unless anyone else has any better suggestions or knows of any likely culprits (have ordered a valley gasket but would prefer not to have to start pulling the engine apart).

[Boosted LS1]

If your rings were that shot I'd expect your engine to burn oil. Have you checked the cam timing? has the engine had a cam fitted at some time in the past?

ETA, are you getting full throttle opening and no restrictions in air flow into the engine?

Edited by Boosted LS1 on Tuesday 7th October 23:37

[Teetertank]

Boosted LS1 said:

If your rings were that shot I'd expect your engine to burn oil. Have you checked the cam timing? has the engine had a cam fitted at some time in the past?

ETA, are you getting full throttle opening and no restrictions in air flow into the engine?

Edited by Boosted LS1 on Tuesday 7th October 23:37

I have had some oil loss as mentioned previously; but have not done enough miles to know how serious. However the oil is really clean, and not been sooted up from leaking exhaust gasses. Plus there is no noticeable smoke in the exhaust.

I don't believe any new cams have been fitted. There’s certainly no record of it amongst the perfectly documented history.

Have checked throttle readings and they read fine. Brand new air filter fitted, and no apparent blockages.

[That Daddy]

You are checking the compressions with the throttle wide open when cranking are you?

[Teetertank]

That Daddy said:

You are checking the compressions with the throttle wide open when cranking are you?

Yes. Throttle held open, engine warm, and all spark plugs removed.

[That Daddy]

Teetertank said:

That Daddy said:

You are checking the compressions with the throttle wide open when cranking are you?

Yes. Throttle held open, engine warm, and all spark plugs removed.

OK just checking