13 replies to this topic

[tino]

Hi All,

 

I have recently taken the engine out to solve the issue with the low oil pressure on start up, which turned out to the be oil gasket has failed. In the process I took the cylinder head off to have a look at the bores and they all seemed, so took the opportunity to re-lap the valves and change the oil stems.

 

However I have low cylinder pressure on cylinders 2 and 4, so I don't think it's a head gasket fault. It's at 75PSI so not dreadful but not great, I have adjusted the tappets and checked them and they are all set to what the haynes manual says. i am not sure if there is a link between NO 2 and 4 so before I take the head off I thought I would ask.

 

Not sure if it's relevant but when testing those two cylinders with no spark plugs in any other the oil cap seems to become pressurised and releases as I turn the engine.

 

Thanks!

[tino]

Hi All,

 

I have recently taken the engine out to solve the issue with the low oil pressure on start up, which turned out to the be oil gasket has failed. In the process I took the cylinder head off to have a look at the bores and they all seemed, so took the opportunity to re-lap the valves and change the oil stems.

 

However I have low cylinder pressure on cylinders 2 and 4, so I don't think it's a head gasket fault. It's at 75PSI so not dreadful but not great, I have adjusted the tappets and checked them and they are all set to what the haynes manual says. i am not sure if there is a link between NO 2 and 4 so before I take the head off I thought I would ask.

 

Not sure if it's relevant but when testing those two cylinders with no spark plugs in any other the oil cap seems to become pressurised and releases as I turn the engine.

 

Thanks!

 

I can't seem to edit the topic, it should say low compression, also prior to taking the head off it was around 140 psi.

 

Edited by tino, 12 January 2025 - 11:51 AM.

[nicklouse]

Ok first off. What oil gasket?

 

that is the compression on the other two?

 

test should be done with no spark plugs in and throttle wide open.

 

you should test left to right then right to left and divide by 2. With a well charged battery.

 

if 75 when was 140 it could be your valve gaps. Or a poor head gasket.

[tino]

Ok first off. What oil gasket?

The one the pump mates to the engine with.

https://www.minispar...-gasket-genuine

that is the compression on the other two?
 
test should be done with no spark plugs in and throttle wide open.
 
you should test left to right then right to left and divide by 2. With a well charged battery.
 
if 75 when was 140 it could be your valve gaps. Or a poor head gasket.

The other two are 135 roughly. I did throttle wide open and no plugs in, went up and down twice and same results.

Adding a few drops of oil to the cylinder, didn't impact the pressure by more than 5 psi across all of them so I'm fairly confident its not the piston rings.

It's either bad head gasket impacting two cylinders or I didn't re-lap the valves very well is my assumption?

I have checked the valve clearance multiple times and they are all correct.

[lsto]

Sound to me like unfortunately you'll be taking the head off again and checking the valve seats. You'll have to change the head gasket anyway but at least when the head is off you can re-check it for straightness and make sure nothing is leaking past the valves.

[tino]

Thought as much, one final thing. After cranking and measuring on either of those cylinders, I can hear a pulsing hiss from somewhere, measured pressure doesn’t drop mind. So I think it’s most likely head gasket.

The head itself was straight/flat and she’s not been started yet since taking the head off so I’d assume is still flat!

[weef]

Instead of doing a compression test carry out a cylinder leak down test before you strip the engine to see if it gives you a better indication to where your fault is.

[lsto]

Thought as much, one final thing. After cranking and measuring on either of those cylinders, I can hear a pulsing hiss from somewhere, measured pressure doesn’t drop mind. So I think it’s most likely head gasket.

The head itself was straight/flat and she’s not been started yet since taking the head off so I’d assume is still flat!

The hissing may well be the sound of the valve seat leaking. It's horrible when you put all that effort into a job and something like this happens, unfortunately it comes with the territory sometimes. Good luck

[ACDodd]

Did you reset the valve clearances after refitting the head?

Ac

[tino]

Did you reset the valve clearances after refitting the head?

Ac

If you mean check them all and make sure they were .3mm/.012” then yes, done that.

Also checked the tappet bolts themselves were torqued correctly and rechecked the cylinder head bolts.

[tino]

Sound to me like unfortunately you'll be taking the head off again and checking the valve seats. You'll have to change the head gasket anyway but at least when the head is off you can re-check it for straightness and make sure nothing is leaking past the valves.

How can I test nothing leaks past the valves out of the engine? Or is it just lapping until shiny?

[lsto]

Make sure there is spark plugs fitted, (with the valves and springs fitted) then turn the head upside-down. Then fill the chambers with water and leave it for a bit and see if any leaks past the valves into the inlet or exhaust ports. I like to use a solvent so it's a bit thinner and will show leaks quicker but bear in mind if you do it's a potential fire hazard.

[tino]

Make sure there is spark plugs fitted, (with the valves and springs fitted) then turn the head upside-down. Then fill the chambers with water and leave it for a bit and see if any leaks past the valves into the inlet or exhaust ports. I like to use a solvent so it's a bit thinner and will show leaks quicker but bear in mind if you do it's a potential fire hazard.

I assume brake fluid is ok? Pretty sure I used that last time, but can't find the photo's I usually take before and during so it looks like I missed it.

[tino]

Also, pretty sure this doesn’t matter but no harm in asking.

It’s a copper head gasket and the car hasn’t been started yet so no heat cycle. I assume that won’t make a difference at all?

I think I’m going to go with this one next time https://www.minispar...ore-head-gasket unless told otherwise!