Rebuilt engine

[Bit of Both]

Hi
I am in the process of buying a rebuilt engine. All machine work was done - bearings replaced as well as the pistons and rings.
A cold compression test that gave 90psi on all four cylinders. Will the compression increase once the motor is run in?

[MarkyB]

It will but I'm not sure how much, what has been done to the valves?

[Bit of Both]

Apparently the valve guides, seats and seals were done.

[bmcecosse]

These readings are dreadful....but what conditions when taking the test? You need a fully charged 'good' battery, hot engine (so the oil is thin) and the throttle held open - and of course all 4 plugs out when doing the test. You could also check the gauge on another known good engine.......

[Bit of Both]

The engine was only run once for a very short time. Later (+- 2 hours) the compression test was done.

[MarkyB]

Was it rebored, you don't specify.

[Trickydicky]

With those compression readings have you checked the valve gaps to make sure they are correct?

[Bit of Both]

The engine was rebored and honed, the head had its valve seats recut and then vacuum tested to check seal.
This is an engine I am looking to buy. I cannot sy whether the valves are set correctly.

[MarkyB]

Does the vendor have anything to say about the bad compression, what sort of guarantee does it come with?

[Bit of Both]

He reckons that it should increase as the motor is run in. No guarantees

[bmcecosse]

It should be ~ 160/170 psi if in good order.

[MarkyB]

It needs to come up by about 50 psi which doesn't seem likely.
Were the valves ground is are they relying on the machined finish I wonder?
If it's you doing the compression test you could try putting some oil down the bores to give the rings more seal in an effort to see where the pressure is going.
If it hasn't been done right it wont be worth the money, and with no guarantee you have no come back at all.

[bmcecosse]

Possibly wrong size pistons fitted? Or rings broken on assembly? Maybe it's just a poor test - with cold/thick oil etc... Ask to see a REAL test on a hot engine after a 10 mile run.

[MarkyB]

So many ways to do it wrong, even 1 thou over bored is equal to many thousand miles driven that you wont get back.
Does he have a long list of happy A series customers perhaps?

[Bit of Both]

The problem we face here is that we do not really have anyone specializing in rebuilding Morris Minor engines. If I look an E-Bay thère are many in the UK but the cost to buy and then Ship it here is to high.

[MarkyB]

Do you have to give him your engine as part of the deal?

[bmcecosse]

Agree to install it in your car and run it for a week doing at least 100 miles.....if the comp readings then reach 140 psi hot (pretty much the acceptable minimum) with good oil pressure (60 psi when hot at 40 mph in top gear) and no oil burning smoke or leaks - you will buy it. Otherwise - he takes it back and you own nothing.