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 1725 Compression test
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Stella

France
127 Posts

Posted - 25 Aug 2017 :  09:23:04  Show Profile  Reply with Quote
Does anyone know the original compression for the cylinders. I did a compression test yesterday and found the following results:
cylinder 1: 152
cylinder 2: 140
cylinder 3: 160
cylinder 4: 150
I feel that this would be within the norm but am curious as to what they were originally.
Any help appreciated
Clive

Edited by - Stella on 25 Aug 2017 09:26:12

pruyter

Netherlands
199 Posts

Posted - 25 Aug 2017 :  09:41:54  Show Profile  Reply with Quote
With a completely new engine the compression pressure should be 175/185 lbs which translates in 12.3 to 13 kg/square cm.
The difference between the highest pressure and the lowest should be no more than about 10%. In your case the difference between cylinder 2 and 3 is 20 lbs which calculates for about 15% when we take 140 lbs as a basis to calculate from.
If you experience no specific problem I should do nothing with it.
If you are interested to know what could be the cause of your observations than the following procedure gives you more information:

Run the engine to operating temperature;
Take out all spark plugs;
Put a tea spoon of oil in a spark plug hole and measure again;
Proceed with a tea spoon of oil until you have measured all 4 cylinders.

When the compression pressure is higher than the measurement without the tea spoon of oil then the problem can be related to pistons and/or piston rings.
If the compression pressure remains the same then most problably the valves are the culprit.

Regards,

Peter
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Stella

France
127 Posts

Posted - 25 Aug 2017 :  11:13:07  Show Profile  Reply with Quote
Hi Peter

My car keeps losing force after driving a few kilometres on recent outings.. so that we have had to turn around and go home for the modern. (not nearly so much fun). On the return trip it will appear to be OK then suddenly go into limp mode...and I panic about needing to get out and push.

Sending for a carb renovation kit..have checked almost everything.. at a bit of a loss to know the cause for this off-an-on performance.
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pruyter

Netherlands
199 Posts

Posted - 25 Aug 2017 :  14:09:30  Show Profile  Reply with Quote
Hi Stella,

This problem has in my opinion no relation with a lack of sufficient compression pressure, if it should then I should expect it to be a constant problem.
This problems, that are not there all the time, are not easy to solve.
It has to be most likely either petrol or ignition. So that asks for a systematically approach. Regarding the petrol section it could be dirt in the petrol, lack of sufficient ventilation via the petrol cap which can be determinated by taking the petrol cap of when the problem has occured. If you hear a sucking noise from the tank opening then you have found the problem. Alternatively you could make a test drive without the petrol cap installed and see if the problem disappears. But there are many more possibilities like problems with the petrol pump and carburator.
So if the problem only occurs after you have driving some time then I should think about a ventilation problem with the tank or something that is related with temperature (for instance the ignition coil getting hot). From here behind my computer it is not easy to find out what is wrong, but with some base knowledge about car engines it must be possible to detect the culprit.
Don't hesitate to come back to this forum with your observations while you are searching for the culprit. We are with many on this forum,so there is a lot of experience which can be helpful for you.

Regards,

Peter

Edited by - pruyter on 25 Aug 2017 15:33:39
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Stella

France
127 Posts

Posted - 26 Aug 2017 :  07:57:01  Show Profile  Reply with Quote
Hi Peter.. thanks for the feedback.

By the way.. when the hiccup last occurred.. I noticed the rev counter would go crazy... then when the hiccup subsided the rev counter returned to normal ... bizarre...

Clive is going to start working his way through your suggestions..

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pruyter

Netherlands
199 Posts

Posted - 26 Aug 2017 :  08:21:58  Show Profile  Reply with Quote
Hi Stella,

another thing you could try is checking the spark plug of cylinder 2 (the one with the lowest compression pressure)for oil that might have been escaped a side of te piston rings.

The fact that the rev counter is going crazy could be because of a ignition coil problem,the rev counter gets it feed from the ignition coil. So you could try another coil and see what is happening.

Please keep us posted about what is going on.

Regards,

Peter
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bigt80

United Kingdom
932 Posts

Posted - 28 Aug 2017 :  10:13:34  Show Profile  Reply with Quote
Wise words as ever from Peter.
My thought would be electrical; esp. since the Rev Ctr goes crazy when it happens. I've had it before where coil is fine to begin with and as it warms up, it starts to break down. If it were not for the Rev Ctr behaving oddly I would have said it is an air-lock in the fuel system. Electricnick & I had to come back from Moffat the other year with the fuel cap removed, in order to avoid the car loosing power after every 30/40 miles.
Cheers. G
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pruyter

Netherlands
199 Posts

Posted - 06 Sep 2017 :  10:29:36  Show Profile  Reply with Quote
Hi Stella,

Did you already found out what was the culprit of the behaviour of the engine of your Rapier?

Regards,

Peter
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jimlagos

United Kingdom
133 Posts

Posted - 06 Sep 2017 :  17:59:44  Show Profile  Reply with Quote
Hello folks, I've just returned from a tour of France. The fault certainly sounds like electrical, as the rev counter shows. I'd go for coil after checking points condenser first. Peter, as usual, is very good with his advice.

jim

Edited by - jimlagos on 06 Sep 2017 18:00:17
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Stella

France
127 Posts

Posted - 07 Sep 2017 :  19:54:24  Show Profile  Reply with Quote
Hi All...
New coil, refurbish carb, flushed out petrol pump etc.. checked all electrics. Now starts and ticks over... but
major problem between Cylinder 2 and 3... possibly head gasket, possible piston wear.. possibly all sorts of things.. including a cracked head (have I got that right?).

OH is in the process of now removing the engine for a complete overhaul... oh what joy...

Thankfully we are being allowed to use my little SLK for this weekend's Sortie Chabrol... though we are having to be tail-end Charlie so as not to offend the purists...
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pruyter

Netherlands
199 Posts

Posted - 08 Sep 2017 :  12:15:30  Show Profile  Reply with Quote
Hi Stella,

I am sorry to read that there are still problems with the engine of your Rapier. Is it still the same problem as described in your earlier posts or regards it something else?
What are the symptoms that made you conclude that there is a problem between cylinder 2d and 3? If that problem is caused by for example a head gasket than a complete overhaul is not necessary at all?
So if you inform us about symptoms and tests you might have made we possibly can offer some help....

Regards,

Peter
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bigt80

United Kingdom
932 Posts

Posted - 08 Sep 2017 :  14:40:38  Show Profile  Reply with Quote
Yes, indeed - whilst I'm sure from the tone of your last post that it is a bit of a whirl-wind there in the Wood household; as Peter infers: did those initial procedures sort out the problem that you first referred to? These latest diagnosis's would not have caused the first problem, I would not have thought!
Engine out sounds rather drastic; so I'd remove head and then examine head gasket bores etc. with engine in situ and then decide next steps :-). Let us know. G.
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Stella

France
127 Posts

Posted - 08 Sep 2017 :  20:53:45  Show Profile  Reply with Quote
Evening All..

Frankly.. we did not know what was going on. One day the car was running OK... another day, nothing but trouble as the car laboured on.

It seems to have been caused by more than one problem...as OH has gradually worked through the electrical side of things. and it still was not happy.
Not sure what prompted him to look into the compression, except that we knew the head had not been changed to accept lead-free petrol and he wondered if that had now become necessary..

and I got it wrong.. it is bad between 2 and 4 cylinders. the leakdown test shows compression going from No 2 exiting through No 4.

rings and bores appear to be ok BUT going to check everything including all bearings whilst the car is not needed elsewhere.
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pruyter

Netherlands
199 Posts

Posted - 08 Sep 2017 :  21:25:13  Show Profile  Reply with Quote
Hi Stella,

The fact that the cylinder head is not adjusted to take lead free petrol should not cause any problem, because the valve seats in alu heads are already hardened enough.
The compression going from cylinder 2 til cylinder 4 is strange indeed.
If the gasket should be the culprit I should have expected problems like coolant in the oil or the other way around. Loosing coolant, running hot, water in the exhaust etcetera. I must admit that right now I have no explination for this observation. I am very curious what your husband is going to discover and I hope you will keep us informed.
In the meantime I wish you all the luck you need!
Best regards,
Peter
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bigt80

United Kingdom
932 Posts

Posted - 10 Sep 2017 :  09:17:10  Show Profile  Reply with Quote
Oh dear; the behaviour of the engine is most odd: I do hope you get to the root cause of the problem.
Not sure on French fuels, but would have thought no different to UK & with mileage you cover, I totally agree with Peter; there is no requirement, on the aluminium cylinder head, to have it converted to unleaded - just a way of making money for firms who offer the serive - IMHO .
Anyway, yes keep us posted when you have time.
Incidentally I'm coming to France in October - driving to Perpignan, so if you are around when I'm passing I will try to look in on you (seeing Rog & Delia on the way down). G
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Stella

France
127 Posts

Posted - 10 Sep 2017 :  20:16:04  Show Profile  Reply with Quote
Rest assured.. I will keep you informed of progress..

and Glen.. look forward to possibly seeing you in October.. we are back in UK from about 18 - 31st though..

regards

Stella
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