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5 Cylinder Rb20

GTAHH

By GTAHH,
in R Series (R30, R31, R32, R33, R34)

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GTAHH

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G'day lads,

I'll cut to the chase, I bought a really cheap R32 with an RB20 that is only running on 5 cylinders. I have done a compression test and all cylinders are around 127-130 psi, which I think is pretty good? Except for cylinder #3. It has 0 psi compression. And yes I mean 0

I was wondering how I can determine whether it is top or bottom end problem? I am going to embark on taking the head off as I have a feeling that a valve is not closing correctly on that cylinder, if this is the case it should be a fairly easy job. But if I was to rip the head off with the engine still in the car, than it could get a bit messy.

Is there a quick way of trying to work out whether the piston is cracked/rings gone without removing any parts? I have tried the squirting oil into the cylinder and doing the compression to no avail. As it has no compression anyway.

Cheers :D

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Drift R Collaborator

Drift R

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You should get a cylinder leakage test done to determine where the compression is going.

this is where you get the engine on TDC No 3 cyl and feed compressed air into the cylinder and listen where its coming from i.e. remove oil cap if you can hear a fair bit of air then it has excessive blow by on that cyl (prolly cracked rings), if the majority of air is coming from radiator cap then blown head gasket, from intake tube then the intake valve is not sealing, from exhaust then the exhaust valve is not sealing.

you must make sure the piston is at TDC compression stroke so that the valves are closed and when you feed the compressed air in make sure the crank doesn't try to spin back a turn or forward as it will if its slightly off TDC. Also where the compressed air is fed in through the spark plug hole it must have a tight seal (use the compression tester rubber or tube and seal it) so you can hear the air inside the motor.

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GTAHH Collaborator

GTAHH

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You should get a cylinder leakage test done to determine where the compression is going.

this is where you get the engine on TDC No 3 cyl and feed compressed air into the cylinder and listen where its coming from i.e. remove oil cap if you can hear a fair bit of air then it has excessive blow by on that cyl (prolly cracked rings), if the majority of air is coming from radiator cap then blown head gasket, from intake tube then the intake valve is not sealing, from exhaust then the exhaust valve is not sealing.

you must make sure the piston is at TDC compression stroke so that the valves are closed and when you feed the compressed air in make sure the crank doesn't try to spin back a turn or forward as it will if its slightly off TDC. Also where the compressed air is fed in through the spark plug hole it must have a tight seal (use the compression tester rubber or tube and seal it) so you can hear the air inside the motor.

Thanks champ I thought that's how I could do it. Whats a good way to get the #3 cyl to TDC with the motor still in the car?

Also how would you be able to determine the exhaust valve is leaking with the full exhaust on? Other ways?

Cheers again

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Drift R Collaborator

Drift R

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Yeah, pull out the third spark plug and insert a piece of straight wire, turn the crank clockwise so you can see when the piston reaches the top (when the wire stops moving up). Remove the cam covers and look at the cam lobes over the third cylinder, make sure they are not pushing the valves down at all (valves closed). When you have this its at TDC cylinder 3 compression. The piston gets to the top twice in a cycle once on compression (valves closed) and once on exhaust stroke (exhaust valves open)

Good luck

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Drift R Collaborator

Drift R

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give the head bolts a thourough inspecton for anything obvious but they should be alright.

try scotts auto one, repco, coventry auto parts for just the head gasket but it would be worth getting a full VRS kit that contains all the gaskets you'll need, get these from engine specialists possibly the above mentioned.

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Drift R Collaborator

Drift R

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The head most definitly needs to come off if its a valve prob.

A VRS kit is like a bag full of all the seals and gaskets you will need like intake gasket, exhaust gasket, head gasket, cam cover gasket/s, thermostat gasket, water pump gasket (if you change it), new cam seals, 'd' rubbers, cam cover bolt seals and any other gaskets and o-rings you may need to disturb to get the head off. Its cheaper than buying each seperately and way better than using the old ones. Be sure to buy a little bottle of 'permatex' or somthing similar to put on the water gaskets (thermostat, water pump, o'rings on water pipes etc).

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