loss compression in cyl 4 and 5

[markus_74]

Hello,

After a few months begin with smooth shake (very low compression in cyl 4 and 5), now shake more.

It feel like there are no ignition in 1 or 2 cyl, but all spark is normally. No burning oil, temperature normal, just shake from low rpm to high rpm and shake is feel very strong at 1500-2000rpm.

I want to fix this engine but here no leak down tes tools

So what should I do? I want to located the problem between :

1.head gasket leak
2.valve
3.broken ring
4.false reboring by machineshop too big may be.

Any method or visual inspect to check the problems? So I can start with or may be head first?

What sign if head gasket leak?

My engine has compression lost from the beginning after i reboring my block to 2500.

Any idea and advice very appreciated

Thank you
Markus

[SilverShadow]

How do you know that it has too low compression?

Have you carried out a compression test on all cylinders?

In regards to head gasket whats your oil and water state?

[SilverShadow]

How do you know that it has too low compression?

Have you carried out a compression test on all cylinders?

In regards to head gasket whats your oil and water state?

[Yeti]

compression test it dude unless you already have otherwise your jumping the gun. the heads are known going between 4 and 5 so if the compression is rubbish make sure the head gets a leak test when it gets machined.

[Brianmoooore]

Leak down tester on 4 or 5, forcing in compressed air, then listen through the spark plug hole of the adjacent cylinder. If there's a leak between the two, you'll hear it hissing.
Turn the crank a bit, just in case the noise is travelling by partly open valves, and repeat.

[markus_74]

Hello,
Sorry for late reply because of the different zone time.

Yes, i have doing compression test this is the result

Compression test (warm and 6x crank)
Cyl 1 160psi
Cyl 2 165 psi
Cyl 3 160 psi
Cyl 4 125 psi after add oil 160 psi
Cyl 5 120 psi after add oil 170 psi
Cyl 6 140 psi

No smoke come from exhaust, no oil in the water, no water in the oil, all spark plugs good health brown, temperature normal, no oil loss.

Just smooth shake like 1 cyl dead, and shake is faster as fast the rpm.

I just buy small air compressor today 100psi power, i hope it is enough to make pressure into the Cyl and trace the leak i really curious what is make it shake.

But just for opinion does lower compression have shake symptoms?

[Speedtouch]

Sounds like sticking or worn piston rings or possibly bores on Cyls 4 & 5.

Cyl 6 is rather low too.

[markus_74]

Sounds like sticking or worn piston rings or possibly bores on Cyls 4 & 5.

Cyl 6 is rather low too.

It start from the beginning the engine running so i think

May be the machine shop too big while making new boring? Or false while make honing pattern?

What horse power loss in this case? Just raw number.

And what is the machine shop need for doing good reboring? Only piston ring and measure the gap between ring or ring must attach into the piston?

[DanThe]

What head gasket was used?

[markus_74]

What head gasket was used?

I use victor reinz brand new

[markus_74]

I want to make simple leak test but o just have small compressor and if i fill air in the healthy cylinder, does the air will flow out from the cylinder or stay inside 100 %?

[Brianmoooore]

Air will flow past the rings, and air will leak past the valve seat. The trick is to judge just how much air is leaking, and whether it is acceptable, and you can do this by comparing with the good cylinders. Air should not leak directly from one cylinder to another, and the air leaking past valve seats should be minimal, providing, of course, that the valves in question aren't being lifted by the camshaft.

[markus_74]

Thank you for the info tomorrow i will make test with help of my mechanic. I will info what i will.get

[guuskolo]

i had the same on my 200.000km m10.
i bought tunap valve cleaner ( seafoam is the american variant ). it is supposed to loosen piston rings too!
i had:
Cyl 1 10
Cyl 2 8
Cyl 3 10
Cyl 4 8
and now i have 12.5 on all cylinders.

i can't guarrantee it'll work for you but trying it is a hell of a lot better than a head rebuild.

[markus_74]

Thank you for the info but my engine is newly rebuild, so it is something wrong with the tolerance but maybe not sticking ring

[markus_74]

After try to blast compressed air to cyl

Cyl 1, 2, 3, 6 air goes to exhaust and intake but not a lot

Cyl 4 and 5 no air goes to cyl 5 to 4 or vice versa, air goes to oil dipstick hole and intake and exhaust, no air goes to other sparkplug hole.

No air bubbles in the water radiator.

It is difficult for me to judge which is wrong or good

In this test im still un sure.

But in compression test meter, i can sure while.i put a spoon of oil, the pressure goes high at cyl 4 and 5.

So what does the conclusion? Any advice?

[Speedtouch]

Sounds like sticking or worn piston rings or possibly bores on Cyls 4 & 5.

[markus_74]

I use about 100 psi and it goes empty at about 5 second, why it not like the leak test tool that can hold much pressure in very long time may be about 1 minute?

[DanThe]

The compression tester has a valve that holds the pressure in the gauge

[Yeti]

i presume you rotated the engine on each cylinder to TDC when you did the leak down test?

they could of not set the piston ring gaps 120 degree orientated from each other as you will get a leak through but theres a certain amount of leakage thats allowed. i have seen that before. so either way it would be a strip down.

[markus_74]

i presume you rotated the engine on each cylinder to TDC when you did the leak down test?

they could of not set the piston ring gaps 120 degree orientated from each other as you will get a leak through but theres a certain amount of leakage thats allowed. i have seen that before. so either way it would be a strip down.

Yes each cylinder to TDC.

I don't understand piston ring gaps 120 degree oriented but all.

I got once at cyl 4 very little leak but, while i make compression test this cyl is very low seem it is opposed (while i put a spoon of oil pressure raise)

[Gavt]

If pressure is good with oil in there then it's rings or a cylinder wear. Both require a strip down to find out it could be the rings not 120 degrees out (what would be the cheapest option) but strip down is still required ,when you replaced the rings did ensure that the opening of each ring was offset 120° from each other like the points of a Mercedes bagde

[markus_74]

I see i understand now, that the ring gap shoud not parallel and should have 120 degree, i will ask my mechanic as he is installed it. But he has installed many engines before.

[Brianmoooore]

Get a piece of tube, one end in your ear, and the other into various parts of the engine to hear where the air is escaping to. Compare with other cylinders to determine what is 'normal'.

[Yeti]

yea sorry im crap at explaining things some times lol

hope this helps

[markus_74]

Get a piece of tube, one end in your ear, and the other into various parts of the engine to hear where the air is escaping to. Compare with other cylinders to determine what is 'normal'.

It is very difficult, all air goes to in and ex valve the other i don't known

[markus_74]

yea sorry im crap at explaining things some times lol

hope this helps

Thank you for have send me the picture

[markus_74]

I will open the head next week to check what is wrong.

I have feeling 90% that the fault is in the ring or cylinder wall because while i pout/put a small quantity of oil into the sparkplug hole and make compression test the pressure goes high/normal again.

If i put oil and pressure not goes high so it is not the ring or cylinder wall, it isn't correc

[Gavt]

Yes oil will temporarily help seal the rings and bores by blocking any small airgaps . if its valve related oil will not make a difference to the pressure

[markus_74]

Thank you this make me courage to open the head.