End compression pressure

[Bpaccaud]

Checking the compression ratio from the car i would to buy, here is what i find

cyl1: 7 bars

cyl2: 7 bars

cyl3:6.5 bars

cyl4: 6.5 bars

cyl5:6.3

cyl6: 6bars

it seems to me, to be Low no????

What value could i must to find with a 2.6 l with E88 head

260Z 2+2 1975????

Ben

[JEFF]

Tell me your compression per cylinder in P.S.I and i might be able to help. I do not know what 'bars' are. (well not in the context that you used the word anyway).

- Jeff

[Smokey]

I am actually curious about this question. Of course, I am lost on bars too. From what I have seen, looks like 150's are good numbers for these engines. Or at least, those are the numbers that I have seen generated in the L series motor.

Someone, fill us in on what is a good number range for compression.

[RB30-ZED]

Hi guys

There are 14.5 PSI to the BAR.

So we have cyl 1 101.5 PSI

cyl 2 101.5 PSI

cyl 3 94.25 PSI

cyl 4 94.25 PSI

cyl 5 91.35 PSI

cyl 6 87.00 PSI

The fact that the compression is only around 60% of what it could be ( 150- 160 ) is not good.

The range from highest to lowest is more than 10%, but would indicate general engine wear rather than a problem, like head gasket or valves.

Steven

[sjcurtis]

I agree with the pressures as they appear the engine wear is constant all cylinder are deteriorating together as far as pressure goes it is low but ask why they are all low could be the gauge.

Warm the engine before doing the check. Did you see a decompression plate between head and engine block. The L series engine will drop pressure to the rear (6) with age so don't worry to much. As long as the pressures are close together it will all go smooth. The 10 % is a guide, this engine if it does not blow to much smoke could still run for a while

good Luck

Steve:classic:

[Bpaccaud]

Sorry for the European unit! Like Steven explain 1 Bar is = 14.5 PSI

To explain the problem, the engine didn’t turn for 3 years and has 124000 km, and it has a Janspeed turbo kit.

I check the pressure when it was hot, with full open throttle. And I was taking it twice.

Cold the engine smoke badly and when you revs at 3000 rpm and up a wreath of smoke goes out….but after 30 minutes turning, the smoke begin to disappeared. I suspect the valves seals

The carburetor is in bad condition and the combustion was so not good.

Explain me what you are thinking by compression plate? On the gasket???

When the seller had parking the car 3 years ago it was because when it was hot the engine warm and turn badly, ( but with the carby, and general condition and tuning of the engine I suppose It couldn’t be good)

The next time I’ll check with another tester to find where the pressure is lost and I will inspect the cylinder by the spark plugs with a little light.

Perhaps the rings are glued, and the engine need more turn and time to breath new, I can’t take the road actually to test the car and the engine in reel condition.

What did you think of all that?

Ben

:dead:

[Smokey]

One thing to consider here since you say the car has sat for an extended period of time. It might not be the valve seats that are the cause of the low compression.

One of the Z's I have looked at fell into that very same condition. The owner said that when he bought the car, it ran, although poorly. He pulled the head to get it machined and overhauled. While at the machine shop, the guy said that the head was pretty much shot from having sat so long. The acids in the oil had started to eat away at the head.

The owner then went home and started to look at the block. He actually found a small hole in the side of the block. Come to find out, the acids in the oil along with the coolant had rusted out the block from the inside out. There was no way to save this engine. he ended up with a new Jasper L26.

Not sure if this is what is going on with your engine (and I hope it isnt), but be aware that sitting is one of the worst things for an engine unless it is drained and prepped.

[ZCCOR#109]

Ignoring the details of what is exactly wrong with this car, consider the fact that it sat for three years with no preservation. And, that there was a problem with it at that time.

This would only be a headach for any owner, leading to a complete tear down for dianosis, and then a money hole.

P.S.

You need to run a leak down test now. That is done by putting compressed air to one cylinder at a time and examining for where the air leaks. Into the next cylinder, headgasket, out the carb/intake valve, out the exhaust/exhaust valve, into the radiator/headgasket, etc.

If you do this very carefully, you will know a lot more about the situation.

Best of luck.

[JEFF]

My manual shows the compression should be between

171 and 185 PSI for a stock 240Z in 1972. On thruogh 1978

the compression ranged from 165 PSI to 187 PSI.

I just honed and reringed my 240Z, it is bored .030 over with

a 1978 N47 head - compression after assembly = 165 PSI then

after 30 minutes of running = 182 - 185 PSI.

I am very happy with these numbers.

- Jeff

[sjcurtis]

With a decompression plate you can get low pressure readings on the guage, when boost is applied it will normally improve pressure significantly. It is a steel plate that looks like an extra gasket below the head.

good luck

steve :classic:

[Bpaccaud]

If I well understand you think that when the car was modified at Janspeed shop they probably add a decompression plate to reduce the pressure?

But 8.5 compression ratio is not enormous for a turbo!

I actually try to contact Janspeed to have explanations about the assembly and the different modification done on this engine, I send them a mail but no answer at that time.

Next time I will see the car I’ll be careful to this plate.

Thanks

Ben

[sjcurtis]

I think , if your engine still has life, and we can be positive that a decompression plate is fitted, then you will see lower numbers for pressure. You could probaly expect, Janspeed set the engine up in the range between 7.8 and 8.5 as the Compression Ratio. So I think this could be why the numbers are low, as well as worn engine.

Lowell Marx,

is on the money whith his suggestion, can you try the bleed down check.

I still think though you will have to callculate the engine rebuild into your purchase price, as it may operate for a while, but it may not pass the inspection for road use in France. This is your guess.

It would be very good if Janspeed can give you information for this car.

Good luck

Steve

:classic: