Sickly engine - any ideas please?

Post by **Dominic** » Mon Jan 15, 2007 5:45 pm

Thanks Peetee & Jimk, those areas are fine (just checked!). I did however find that indeed the compression is way down on cylinder 3, which has always been a problem with burning a lot of oil. In fact I used about 5 litres this weekend!

I checked the valve settings, which were last checked 2000 miles ago, and found them to be 13, 14, 14, 14, 10, 15, 14, 14.5 (thou) instead of the previously set 12 thou. Proves the point that no.3 cylinder is low on compression! I guess I'd better go and remove that cylinder head! Back later. Dom.

Post by **chickenjohn** » Mon Jan 15, 2007 6:07 pm

That amount of oil burning, could, unfortunately mean piston ring or piston problems- even a cracked piston.

Post by **Dominic** » Mon Jan 15, 2007 7:15 pm

chickenjohn wrote:That amount of oil burning, could, unfortunately mean piston ring or piston problems- even a cracked piston.

If that is found to be the case, is it feasible to replace just the rings? Or does one have to replace the piston as well? or even all 4 pistons / rings?

Post by **bmcecosse** » Mon Jan 15, 2007 7:50 pm

My reference to a 'novice' - was not aimed at 'ben' - it was just a general term for any new starter to cylinder head changing!! And as 'ben' has admitted to me in a pm - he didn't change his head gasket in 'an hour or so' anyway. However - we have shaken hands and made up - storm in a teacup I think!!
If the rings have failed they will almost certainly have taken out the piston lands too. If you are lucky they will not have scored the bores too badly. In which case - a quick fix can be done with one new piston and rings - the piston could even be a 'slightly used' one to keep you going. But I would plan for an engine overhaul sometime soon - or another engine made ready for a quick swap.

Post by **Dominic** » Mon Jan 15, 2007 8:14 pm

Found the problem... A burnt exhaust valve!

I haven't removed it yet, but the head looks to be ok underneath the burnt area which is about 20 degrees of the circumference and into the valve by about 2 - 3 mm. The bore of the cylinder looks very clean, no sign of scoring that I can see, with hardly even a lip at the top edge. It had allegedly been reconditioned a while before I bought it, seems about 10k miles prior to sale, with no maintenance! I've also done about 10k in it, with loads of maintenance! Looks as if I need to remove the sump and extract that piston before I have it back on the road. I presume suppliers would be able to assess what size was needed from showing them the original?
bm... what exactly are the piston lands please? Are they the slots into which the rings fit?

Post by **bmcecosse** » Mon Jan 15, 2007 8:30 pm

Yes - the solid bits ('land') between the ring slots. Really - the slots get widened and the bits in between can break away. But you have found the problem - burned ex valve. I don't see the need to take the piston out now. I would probably consider fitting 4 new ex valves - some hefty grinding ahead - or have the seats refaced at local garage. If you have/get another head then you can take the time with this one - and keep the car on the road meantime.

Post by **Dominic** » Mon Jan 15, 2007 8:37 pm

bm, the head was only put on 14 months ago, newly recon unleaded from MGM. Do you think there is a danger that the other valves are likely to follow suit so soon?
As for the piston /oil consumption problem, could the excessive oil have caused premature failure on the valve do you think? The No 3 cylinder / piston has, ever since I fitted the engine last year, shown a very oily / black looking plug, while the others are a biscuity colour. Also there is oil present in the coating on the exhaust, so I think that maybe it would pay to replace the piston, a few thousand miles of driving should pay for it with less oil to pour in!

Post by **bmcecosse** » Mon Jan 15, 2007 9:06 pm

Ah well yes - there may be a problem with that piston then - best have a look. It wouldn't contribute to valve failure. Another 'unleaded' head failure - I would take it back to them and complain very loudly if it's only that old - and probably not done many miles either!!

Post by **chickenjohn** » Mon Jan 15, 2007 9:25 pm

Looks like I was right on both counts, burnt exhaust valve and piston ring problem!

Why can I not diagnose my own cars as well??

Post by **Dominic** » Mon Jan 15, 2007 9:40 pm

Had a more careful look, the piston bore is in fact scored lower down, the scoring fades away to a perfectly smooth bore for the top 1 1/2". The scoring is itself nicely smoothed off, so is hardly visible. You can really only notice it by running a finger sidewise around the inside of the bore, but then it is very noticeable! Strange, the compression test I did a few months ago didn't show any appreciable drop, compared to the other three! Still, it is enough to get through a pint of oil every 140 miles in normal use (i.e. not a six hour non-stop run except for fuel!)
Now, do I rebuild the original engine? (less cash but more time!) or buy a rebuilt one from a reputable supplier (no more reconned {conned being operative word} engines from ebay methinks!) There is the question.... to buy or not to buy....

Post by **Matt** » Mon Jan 15, 2007 10:15 pm

Or buy a 2nd hand engine and rebuild that whilst still using yours?

Post by **Dominic** » Mon Jan 15, 2007 10:26 pm

Matt, I already have the original engine that needs total overhaul... this was meant to be a good replacement for it, it was sold as "newly reconditioned" on ebay a little over a year ago. Newly repainted more like! I was conned! On the other hand, I gained a lot of valuable knowledge doing a partial rebuild on it before I could fit it! In many ways, it would be good to replace the original engine after rebore, re-surfacing block, fitting new pistons, bearings etc. Trouble is, that costs time, and that is in short supply these days! Maybe I'll just have to toss a coin to decide

Post by **bmcecosse** » Tue Jan 16, 2007 10:22 am

Just stick a valve in the head (or fit another head) and run it meantime - while organising a proper re-manufacture of your original engine.

Post by **chickenjohn** » Tue Jan 16, 2007 1:06 pm

Yes, I would go with BMC's advice. Keep the oil topped up and the engine will run till you've re-built the original. A series will soldier on for ages even when heavily worn. Just don't thrash it, keep speed to 60mph maximum and never use full throttle, especially under load (hills) and the engine will keep going.

Post by **Dominic** » Tue Jan 16, 2007 5:14 pm

Thanks chaps. It does seem a good idea to keep to originality where possible! This engine currently in the car (should be running again before morning) certainly pulls strongly. Except when disabled by a leaky valve, runs smoothly at 70 on the flat, and climbs hills with no difficulty. Full throttle is never used by the way! Nor is it ever allowed to labour in too high a gear.
Thanks again to everyone for all your valuable help!

Post by **Dominic** » Wed Jan 17, 2007 12:12 am

Just in from the garage, it works again!!!! Used an old spare head, probably for leaded fuel, so will use Castrol Valvemaster for the time being until the old engine is rebuilt.
Goodnight All

Post by **bmcecosse** » Wed Jan 17, 2007 8:04 pm

Don't bother with the valvemaster - do set the valve clearances at 15 thou, and check them from time to time.

Post by **Dominic** » Wed Jan 17, 2007 10:47 pm

Isn't it supposed to be 12 thou bm? Or am I confusing myself here?

Post by **bmcecosse** » Thu Jan 18, 2007 7:54 pm

15 thou for exhausts - it allows a bit more for expansion of the hot exhaust valve and less risk of that gap closing up.

Post by **Nadir** » Thu Jan 18, 2007 8:29 pm

All the books and manuals, icluding real contemporary BMC servicing ones, say 12.