question J60 compression readings

[timbo]

Ok so i have, in cylinder order:

130psi

120psi

115psi

130psi

95psi

110psi

 

Any thoughts...?

[FourFox]

Hi Tim

 

I presume these are readings from one of your 'refurb' engines.

 

When an engine has been in long term storage it is usual for one cylinder to give a lower reading than the others (sometimes two). This is because there is always an exhaust valve open and that exposed valve seat and sealing face on the valve will rust.

 

This may sometimes sort itself out, as light rust will be quickly burned off and the seal re-established.

But sometimes it just gets worse as the gasses passing the faulty seal are always in the same place and just wear away the seat. The valves seem to be more hardy and severly burned exhaust valves are rare.

 

Having said all that it is probable that the workmanship on these so called 're-furbished' engines, is indeed very suspect.

I have found all sorts of horrors when dismantling these engines...all of which must have been performed somewhere in the engine re-building process. I'm just glad that my safety in a critical situation was not dependant on such a process.

 

On the subject of correct presevation for engines going into storage, the following might be of interest.

The Rolls Royce B series engines were routinely test run and then heavy engine oil was slowly poured into the carburettor intake until the engine stopped! The spark plugs were then replaced by blanks and the whole engine blanked off with VPI paper and wax!

It seems to work well, as the few of these that I have 'resurected' have been perfect.

 

Jon

[Caddy]

Have you the means to carry out a compression loss test (also called a cylinder leakage test)? It'll give you the ability to find out % of loss and where the loss is going. They are pretty expensive items to buy but they do tell you what the issue is without taking the engine apart.

General idea is to bring piston up to TDC on firing stroke, attach the tester and it will pump a constant rate of compressed air into the cylinder. By listening to the exhaust, inlet, and crank case breather you can tell what isn't sealing.

I was introduced to this tool whilst working on a RR Meteor and it enabled us to make a full diagnosis of the cylinders in less that 2 hours. It also showed where the compression tester had been giving false readings due to the inlet track being blocked.

 

Would have thought that any good garage would have one....

[sirhc]

Tim,

 

Minimum pressure required to pass a test was 130psi. The engine that went with the Sabre project I sold had 160/170psi on all cylinders. Sounds like yours is a bit sick.

 

Chris

eng 1.pdf

[Chrisg]

Have you the means to carry out a compression loss test (also called a cylinder leakage test)? It'll give you the ability to find out % of loss and where the loss is going. They are pretty expensive items to buy but they do tell you what the issue is without taking the engine apart.

General idea is to bring piston up to TDC on firing stroke, attach the tester and it will pump a constant rate of compressed air into the cylinder. By listening to the exhaust, inlet, and crank case breather you can tell what isn't sealing.

I was introduced to this tool whilst working on a RR Meteor and it enabled us to make a full diagnosis of the cylinders in less that 2 hours. It also showed where the compression tester had been giving false readings due to the inlet track being blocked.

 

Would have thought that any good garage would have one....

 

I made mine from an old spark plug and a bit of tube to connect an air line

[timbo]

Thanks all. No it isnt one of my refurbs but the takeout which my rather gutless sabre is equipped with.... Now i know why it is gutless at least!! The plugs are also very black as was the interior of the carb which I replaced..

 

The simplest solution would probably be to uncrate one of my refurbs and see how that goes, but it does mean a bit of faffing to get it from Rugby to Hudds, ho hum, the joys of cvrt ownership.

 

Jon Ive only personally used one of the A2 refurbs so far, in my Spartan, the paperwork said it had a concession for 175bhp, but it seems to go very well (but then it would do compared to this one!). Mr B also had one for his Scorpion, he whined like nobodys business because the carb diaphragms had perished and the coil had gone, but other than that it seems to be ok. I have plenty more to go wrong though!

 

Cheers

Tim