Checking for stuck piston rings.

[ferrispeterchris]

I am re-seating my valves in my V/P MD1 due to low compression.I had such a job getting the head of that I am wary about removing the barrel to check the piston rings. A friend suggested (not sure if it has ever been done before) tightening down a block of wood with a hole bored in it to see what compression I could measure. Is this feasible or crazy? Thanks, Peter.

 

[wotayottie]

If you want to measure the compression, beg borrow or steal a compression tester. They arent expensive and will do the job properly.

Were the valve seats cruddy / corroded? If they werent, then there's no point in putting the head back on to measure compression and ruining another gasket. Were the bores shiny like in a mirror? Do they have a pronounced lip on them?

If all you are worried about is sticky rings (what makes you suspect them?) then I have found that a dose of redex down the bores works well.

 

[PeteCooper]

As already said, use a compression tester - not expensive to buy. When you have tested the compression, put a teaspoon(ish) of oil in the cylinder and then measure the compression again. A significant change in the reading would indicate problems with the rings.

 

[capsco]

I think he is trying to test the compression, without putting the head back on.

 

[ferrispeterchris]

That is correct Peter.

 

[boatmike]

tightening down a block of wood with a hole bored in it to see what compression I could measure. Is this feasible or crazy?

It's crazy big time and won't work. Take the barrels off and look. Even if the rings are not stuck I can guarantee that if your valves are in a naff state your rings will be worn. Check the bores for wear by looking at the lip on the top. If it's not excessive, clean the piston grooves with a broken piece of old ring and fit new rings. If it is, rebore & fit new pistons and rings.

 

[brianhumber]

Can't see what the wood idea is trying to or could be measuring- except for excessive clearance which means your bearings are run and on a small engine like the volvo you would have much bigger signs of this than weak compression. Would suggest
Check bores to see any telltale scrapes indicating broken rings ( unlikely)
Hone the bores to remove any glaze
Regrind the valves
Check head not warped
Refit

As others have said you can check the rings with a compression tester taking readings before and after a drop of oil but unless you have done this before and have a feel for the results I would say do not give yourself more stress but just put it back together and unless you are unlucky away she will go.

Good luck

Brian

 

[Heckler]

it would appear that he has been advised that he can use a bit of wood instead of the head to run a compression check!!
crazy? YES!!
he doesnt want to remove the barrels (?) to check the rings.

 

[Bilgediver]

No ...No......No..

Now you have the head off it takes about 1 minute to lift off the block......Just do it but watch for the shim joint between the block and crankcase....

If you do it then come back and we will tell you the easy way to drop the block back on without damaging the rings...

Now the head is off there is nothing holding the block down other than a sticky joint!!!!