Other car - Mg Midget

[oldmod1968]

Hi, I have tweat or whistle coming with very very slight uneven running on power. Could the tweat be a broken ring or exhaust valve?

Car starts ok, ticks over fine. has 50 - 65 PSI with oil cooler but compression test revels 170 on 3 cylinders 110 on the other (no2) . last year it was 150 psi. Tried a wet test and it increased to 150 psi. In last 3 weels I discovered that the timing was 10 degrees retarded ( thats almost 20 degrees from where it should be for a late 1275) so i assume it was the same on the last compression test.

Any ideas before I dive into a head off or attempt to pull no.2 pist in situ.

thanks in anticipation.

[bmcecosse]

The fact that the compression test figure came up when you added oil suggests strongly that the problem lies with the rings............ Also the timing slipping back like that would tell me to check the vacuum advance mechanism.

[oldmod1968]

Hi, Its really strange. Engine sounds fine and very good. I think it was just badly timed and who ever did it just got the mark the wrong side of the pointer (ugh). I even put a stehascope on the block and there is not other ontoward noise. Could a single set of rings wear like that? I am going to Midget 50 in june and think I might take a chance and not fiddle until I return home on the basis other than the engine sounds good apart from very very slight uneven running . fingers crossed!

[rayofleamington]

severely retarded timing can cause it to run hot
running hot can help damage the rings - they're not unknown to crack
retarded timing will also cause a lot of stress on exhaust valves.

it's a lot of hypotheticals though - without taking it apart it's hard to know.

on the flip side - compression will always rise a bit with oil present.

I'm guessing it's possible to get head off to look at the valves and also piston out from bottom of the block for a looksee at the rings - all with engine in situ if you want to go that route.

[MarkyB]

Can't you find out where the tweat or whistle is coming from?
I doubt you'd hear it if it's coming from inside the engine, more likely a failed gasket somewhere.

[oldmod1968]

I was contemplating using some holts piston seal to imrove the compression as a temp fix. I know there are mixed views on this stuff but recall my father using it many many many years ago on an ford old side valve.

I am taking the carbs and exhaust off to replace gaskets and swith to an HIF so I might take the head off at the same time. I suppose I ought to check for a broken ring but cant hear any ticking. UGH.... why does this happen just before a big run!

Thanks for yr help and would love views on Piston Seal. I assume its some kind of epoxy .

chris

[Stig]

Does an HIF fit without tapping on the underside of the bonnet when the engine's running? I couldn't fit one in on my Sprite so it's still on twin HS carbs. That's not a problem with the Minor's bonnet.

[bmcecosse]

Assuming it's not just a valve gap problem (have you checked?) pop the head and check the valves and seats - and if nothing found - yank the piston from the low compression cylinder. It won't heal up, and piston gunge will do nothing sensible for you.