Compression

Post by **rayofleamington** » Sat Jan 28, 2006 12:40 pm

Hi Onne
From those reading on a low compresion engine, I suggest to completely ignore it and cary on using it.

The 1098 saloon engine has fairly flat topped pistons so when you put oil through the spark plug hole some of it will get around the rings and seal the rings better if they were leaking. The rest of the oil will sit on top of the piston (reducing the remaining volume) and give a mild increase in compression.
The 1098 low compression engine has deep dished pistons so when you put oil in through the spark plug hole it will sit in the top of the piston - the more oil you put in, the more it will fill up the piston until it resembles a standard one, giving a compression ratio closer to 150

Post by **newagetraveller** » Sat Jan 28, 2006 1:56 pm

Changing the piston rings with the engine in place is relatively easy on a Morris Minor (compared with almost any other car).

Take off the cylinder head.

Take off the sump.

Undo the bolts that connect the con rods to the crankshaft.

Withdraw the pistons from the top.

Replace the piston rings.

Put everything back together again.

Post by **Willie** » Sat Jan 28, 2006 4:16 pm

ONNE, I repeat, your readings for a low compression 1098 engine are quite
good. Obviously your problem cylinder is not has healthy as the other three
and the oil test improvement does suggest bore/ring wear but, as others have
said, it will go on for ages. If you fit your nice unleaded head you may well
find the oil consumption improves anyway.

Post by **bmcecosse** » Sat Jan 28, 2006 4:26 pm

Doesn't matter if it was a low compression engine or not - it IS now! But it will run just fine for many happy miles (or kilometers) - and only thing will be the oil consumption (and heavier fuel consumption) which may eventually push you in to doing something about it. Meantime - happy motoring!

Post by **Onne** » Sat Jan 28, 2006 5:12 pm

I will keep on motoring. I somehow think I have another endless moneypit...
Thank you all very much indeed!

Post by **bmcecosse** » Sat Jan 28, 2006 5:17 pm

Lots of cheap 1098 engines on ebay - set up a search under (surprisingly) 1098 ! I appreciate these are in UK - but you seem to have plenty of contacts who would collect/keep for you.

Post by **Packedup** » Sat Jan 28, 2006 7:02 pm

Willie wrote: good. Obviously your problem cylinder is not has healthy as the other three
and the oil test improvement does suggest bore/ring wear but, as others have
said, it will go on for ages.

I would've thought as all cylinders went up roughly the same amount, but the bad one was still roughly the same amount lower, then it points more towards head than cylinder?

If it was just bottom end then I'd expect it to come back into line with the other three on the wet test

Post by **Willie** » Sat Jan 28, 2006 11:04 pm

PACKEDUP.... I disagree there, the rise in pressures with the oil in was not
pro rata, the dodgy cylinder increased more than the other three which,to me, suggests ring/bore wear. ONNE will soon find out whats what when he
fits his new head.

Post by **Onne** » Sat Jan 28, 2006 11:30 pm

Which I haven't bought yet, admittedly...

That is my other query about sending delicate bits like a head. Will it survive the trip?

Onne

Post by **Matt** » Sat Jan 28, 2006 11:52 pm

A head isn't that delicate...... i would say providing the mating faces are protected there shouldnt be a problem!

Post by **Willie** » Sat Jan 28, 2006 11:54 pm

ONNE, well,obviously, it totally depends on how well the supplier packs it!
Mine was well protected and suffered no damage. Perhaps you should ask
the supplier to keep in mind that it is going abroad.

Post by **Onne** » Sun Jan 29, 2006 10:55 am

I will indeed, firts have to save up a bit. I like your pictures Willie! Looks beautiful

Post by **mkwc** » Sun Jan 29, 2006 12:01 pm

If you have added oil to the cylinders and the commpression goes up it normally indicates that the problem is with the rings.
By changing the head at this stage you will probably achive nothing.
A more accurate way to find if engine has a problem is to have a leak down test done on the engine.
This is a common practise in the aircraft industry for checking piston engines aircraft, a leak down gauge is attached to the plug hole and compressed air is pumped into the cylinder if rings are the problem you will hear air escape through the oil filler, if it's an inlet valve it will came out the carby, for an exhaust valve it will come out the exhaust and a crack in the head or block, the rad will bubble.

Maybe that is over simplifying the whole thing but you can see what I mean.

Regards Mark

Post by **Onne** » Sun Jan 29, 2006 2:03 pm

Indeed I can see it. A device that is easily made at home I think, all you need is a compressor, an old sparkplug en a bit of hose.

Excellent

Post by **rayofleamington** » Sat Mar 04, 2006 3:48 pm

I did a compression test on Wilberforce this afternoon. 135, 120, 125, 135 (Similar Readings to Onne, but without low compression pistons!)
Wilberforce still goes better than most 1098's so it puts the readings into perspective.

Post by **Onne** » Sat Mar 04, 2006 3:59 pm

I guess compression is only one piece of the four stroke system. Rather important one for sure.

I still find my 1098 rather lumpy, and a bit fitless. It is quite torquey but doesn't like revving.

Post by **bmcecosse** » Sat Mar 04, 2006 5:45 pm

These are pretty desperately low readings for a 1098!! Mine gets 165/170 psi on all bores - and it's six years (but only 10,000 miles) since the head was off - and that's all on unleaded petrol with NO additives, and no hard seats.

Post by **rayofleamington** » Sat Mar 04, 2006 6:26 pm

These are pretty desperately low readings for a 1098!!

yes - they don't appear good (maybe my guage reads a bit lower than yours?)
either way, he really flies though

Had to keep backing off the gas to keep down to 70 on the M40 just now.

Post by **Onne** » Sat Mar 04, 2006 7:47 pm

Well, I know my block isn't the full 75% atm, but who knows, it might still be original

Post by **bmcecosse** » Sun Mar 05, 2006 6:05 pm

It could well be the gauge/battery condition/starter condition. Test should be done on hot engine - with all plugs out and throttle wedged open - to let some air in ! If it runs well, don't worry about it!

Morris Minor Owners Club

Compression

compression

Re: compression

bores

head