11 replies to this topic

[PACINO]

With the hot engine (1275cc) this was the result:
Piston 1: 125 psi
Piston 2: 135 psi
Piston 3: 135 psi
Piston 4: 140 psi

What do you think?

[sonikk4]

Throttle wide open? Tappets set correctly?

[PACINO]

Hello Sonikk4. Yes, Throttle wide totally open. Sorry but I don't know what is or means Tappets.

[Daz1968]

Valve clearances may be an easier term, I find if compression test is similar across all cylinders then it is usually ok, actual reading is not as important, I would try a little oil in cylinder 1 see if it improves, it seems a little low compared to the others, 

my 998 shows 150 on all cylinders but that has a skimmed and rebuilt head.

[PACINO]

Hi and thanks for your answer. In 2016 I did the compression test twice and it gave me; around 13 bar in each cylinder. Since then, I will have made the car 7 thousand kilometers or less.

In this time I have changed the exhaust for a narrower one, I put an electronic distributor, and I have lifted the cylinder head to give it a review putting new stem top hat seals.

I find it very strange such low compression. Any suggestions?

Edited by PACINO, 27 January 2020 - 01:29 PM.

[DeadSquare]

Let this be a lesson to you.

 

As you have noticed, you get a much higher reading if you work in British PSI, than if you use EU Bar

[PACINO]

The compressimeter used in 2016 is a DRAPER exactly to this one, which belongs to a friend.




In that time the cylinders was around 12-13 Bar. (174/188 psi).
Now, 9 - 9.5 Bar (130/138 psi)

There is a big difference.

Edited by PACINO, 27 January 2020 - 04:15 PM.

[Magneto]

I bought a new compression tester, and the first engine I tried it on it gave readings lower than I expected, so I dug out my old one and ran the test again, then borrowed my neighbor's to double check.....the new one was 50lbs low! My old one and the neighbor's agreed almost exactly.....

[PACINO]

Hi Magneto. Thanks for your answer. Without a doubt, my friend's compression tester, which is a Draper, is better than I bought now, which has been very cheap.
Anyway, there is a big difference between the reading I did in 2016 and now.

Could be it influenced by an incorrect electronic distributor set?

Edited by PACINO, 28 January 2020 - 12:23 PM.

[bpirie1000]

Dont think it will be influenced with distributor.
Your measuring the compression not the time of the spark.

[Twincam]

Hi and thanks for your answer. In 2016 I did the compression test twice and it gave me; around 13 bar in each cylinder. Since then, I will have made the car 7 thousand kilometers or less.

In this time I have changed the exhaust for a narrower one, I put an electronic distributor, and I have lifted the cylinder head to give it a review putting new stem top hat seals.

I find it very strange such low compression. Any suggestions?

When you removed and replaced the cylinder head, did you renew the head gasket and also adjust the valve clearances?

[PACINO]

Hello friends, and thank you to reply. Yes Twincam, a year ago I lifted the Cylinder head and it was sent to the grinding machine. They decarbonized it there, lower two tenths of a millimeter, and put new Dupont brand top hat valves on it. The valves and their guides were not replaced as they were good and there was no wear.

I mounted it in the car with ARP type studs, put a new cylinder head gasket (Payen BK450) on it and made the valve adjustment as the manual says. The Cylinder head must be given a re-tightening at 1000kms.