Compression

Post by **Onne** » Fri Jan 27, 2006 5:56 pm

I did a compression test today:
No oil in bores:
cyl. 1 125 Psi
cyl. 2 110 Psi
cyl. 3 125 Psi
cyl. 4 125 Psi

With oil in the bores:
cyl. 1 160 Psi
cyl. 2 150 Psi
cyl. 3 160 Psi
cyl. 4 160 Psi

So apparently number two is down a bit, the others were exactly the same. My plugs were very dirty though, lots of oil being burnt in the chambers (maybe valve guides???). What would you wise people advise me to do? I have got a leaded head now, so thats another reason for changing heads.

Has anyone ordered ESMs unleaded heads by mail? Or would you advise me not to order it like that? This because it is probably the easiest, cheapest, and quickest way of getting it all done

Onne

Post by **Onne** » Fri Jan 27, 2006 6:16 pm

I forgot to ask, what would the compression have been when the engine was new? Low compression engine btw

Post by **chickenjohn** » Fri Jan 27, 2006 6:58 pm

If the compression goes up with oil in the bores, then thats possibly a sign of piston rings worn!

125 looks too low for me.

My traveller was ~150 psi (apart from the one with the burnt valve- 63psi) adding oil made no difference.

Post by **Matt** » Fri Jan 27, 2006 7:15 pm

but thats a high comp. engine, onnes isn't.....

I think you might have some bore wear there onne, but does it run ok?

Post by **Onne** » Fri Jan 27, 2006 7:17 pm

It doesn't idle nicely. And she uses quite a bit of oil, so it might indeed be the rings.

Shame.... so anyone with another engine?

Post by **Matt** » Fri Jan 27, 2006 7:18 pm

I have one with bore wear ;)

Post by **Onne** » Fri Jan 27, 2006 7:21 pm

well, that'll be perfect.... but I already have one in that state.

Post by **chickenjohn** » Fri Jan 27, 2006 7:22 pm

Take the cylinder head off and have a look! It might be a combination of valves needing re-grinding and knackered valve stem oil seals, if you're lucky! If not, then its re-build time....

Post by **Willie** » Fri Jan 27, 2006 7:39 pm

ONNE, the manual gives compression pressures for the 1098 high compression engine as 150 psi and 130 psi for the low compression type.
The difference on your engine seems to be pro rata although,obviously, there
is an improvement with oil in the bores. So much so in fact that your readings
are equal to the 1098 readings. ( I am assuming that you have the earlier
engine installed)?

Post by **Matt** » Fri Jan 27, 2006 7:44 pm

thats for a 1098....

Post by **Onne** » Fri Jan 27, 2006 7:50 pm

I have got a 1098 Willie, how much difference should there be, if any, with or without oil in the bores?
At least they are somewhat the same
Onne

Post by **Willie** » Fri Jan 27, 2006 8:19 pm

ONNE, ok so you have a low compression 1098. Your readings, without
oil, are within 5 lbs psi of the official manuals figures so your oil usage could
be due to worn valve guides. Are you sure you do not have a high comp.
cylinder head fitted? The difference between the high and low compression
engines is in the amount of dish in the pistons.

Post by **Packedup** » Fri Jan 27, 2006 8:32 pm

It's worth bearing in mind that oil in the bores will up the psi when testing anyway, so that might not be too much of a worry (depends how much you put in I suppose, to get about 30% increase in pressures like that). However, one pot is consitently lower than the others, wet or dry, so that suggests a problem there.

From what people have said, the figures you're getting might be normal for your engine, so I'd be looking at other causes for the poor running, but head related for the oil on the plugs. Which is handy, cause an A series head swap takes next to no time, and gives you a reason to go unleaded nowif you have the cash

Post by **bmcecosse** » Fri Jan 27, 2006 8:34 pm

The readings are very very low - but of course the gauge is not exactly a precision calibrated instrument. However the increase with oil added does point to a badly worn engine - with #2 worst of all. The 1098 heads are all the same - compression difference was in the pistons. My 1098 with skimmed head reads 160/170 psi dry on all bores (and that's after 6 years summer running on unleaded fuel with no additives) - have never tried it with oil. When taking the readings - take all plugs out and prop the throttle open to allow air into the engine.

Post by **Matt** » Fri Jan 27, 2006 8:37 pm

but I bet yours isnt low compression BMC.....

Post by **bmcecosse** » Fri Jan 27, 2006 10:07 pm

Err well no - with the skimmed 295 head I think it is ~ 10:1, or at least it was 6 years ago, but age may have withered it slightly!

Post by **Onne** » Fri Jan 27, 2006 10:29 pm

Well, this compression meter is calibrated, cost me well over £100. And I did remove all plugs, and had the throttle wide open.
So what should I do next? Just carry on, wait until the MM is finished, and then get the engine in Liz rebuilt?

Post by **Packedup** » Sat Jan 28, 2006 3:25 am

I have 6 cylinders (not a Minor, but I'm getting closer to actually owning one, and I'm still swearing at the pickup frequently!) - And though my guage is pretty worn out, it reads about 130 on one pot, 115 on 4 more, and about 105 on the other. I haven't tried putting any oil in and retesting as quite frankly readings that low suggest the engine needs some serious work that I just don't want to do, would rather save up and buy another (a little harder to get and slightly more pricey than Minor engines

). These readings are cold, and you should really test on a warmed up engine...

But anyway, even with those figures I still get a decent tickover and can just about put the calender away when timing 0-60. If you have a low compression engine and you've tested it cold then I wouldn't be too concerned other than that one that was noticeably lower than the others, which could well be head/ valve related anyway. As I've said, A series heads a doddle to get off, so I'd be tempted to get a new headgasket, pull the head and see if there's anything really wrong or if a quick clean up would improve things a little. A couple of hours on a dull afternoon, if everything goes right (or a couple of week getting parts and trying to get it all back together if everything goes wrong I suppose!)

Post by **Onne** » Sat Jan 28, 2006 7:43 am

That would be a challenge... But I strongly suspect my rings too, that is why I tested with and without oil, without to test the rings, and with to test the valves
and always on a warm engine

Onne

Post by **chickenjohn** » Sat Jan 28, 2006 10:20 am

Onne wrote:Well, this compression meter is calibrated, cost me well over £100. And I did remove all plugs, and had the throttle wide open.
So what should I do next? Just carry on, wait until the MM is finished, and then get the engine in Liz rebuilt?

Yes, provided you keep the essential fluids (oil, water) topped up, an "A" series- even a badly worn one- will keep going for many thousands of miles after showing signs of wear. (Provided the cloud of smoke behind the car doesn't get too embarassing!)

Or, you could take the cylinder head off and have a look- a new head gasket set is only about £10 or so. Easy weekend job.