If its not the head gasket, then what is it?
Turbo Mini Forums

I'm hoping someone on here can advise me on a problem I've got with my MPi mini.

It started running rough on the way to work a little while ago, so I returned it home and parked it up. I didn't have my compression tester at the time, but when I took the head off the (Payen BK450) head gasket had gone between cylinders 1&2 (on the right when looking into the engine bay, near where the side mounted radiator would be on an older mini). The gauge didn't register the engine getting hot and when I came to strip the engine down there was coolant in the header tank.

I changed the gasket and put it back together, it ran but didn't sound too healthy. It sounded and felt as if it was running on three cylinders, although it did seem to run slightly better as the revs got to 2000 - 3000rpm. I checked to see that a spark was getting to the plugs (it was) and changed the plugs. On taking the car out for a check run I noticed smoke/steam coming out from the front drivers side corner of the bonnet. On pulling over and popping the bonnet there was nothing to be seen - I can only assume the problem occurs under load. On the trip back home there was also exhaust/smoke making its way into the car too. Once I got my compression tester back I checked each cylinder. No. 1 cylinder recorded 5 1/2 Bar, the other three recorded around 13 1/2 - 14 1/2 bar.

So - am I correct in thinking if the head gasket had gone again it would show as two low cylinder compression readings?
I cleaned the cylinder head and block before putting the new hard gasket in, but am I going to have to strip it again and check the head hasn't warped?
If its not the head/gasket, what could it be? I've had it suggested that the exhaust manifold may be cracked (I've had a Maniflow crack between the Y of an LCB - I've got a Specialist Components stainless manifold on now).
Could it be a sudden failure of the piston rings on No. 1 cylinder?
What else could it be/should I be looking for? (I'm going to have another good look tomorrow to make sure I haven't left any of the emissions pipes/tubes off, but I don't think it's going to be that simple!).
Anyway, sorry it's not a turbo/supercharger question (perhaps one day) but I'm hoping the collective knowledge on here can point me in the right direction.

Thanks in advance,
Graham

Schrödinger's cat - so which one am I ???

Rod, this was the failed HG:

At the time I did wonder why one cylinder/piston/valves was so much cleaner than the adjacent cylinder (as can be seen in the above photo). This is the valves relating to the cleaner cylinder:

Do these photos help?

Did the valves in cylinder one look OK? Poor valve seal or the tappets being incorrectly set might cause these symptoms.

Smoke/steam under the bonnet could be some spilt oil/coolant burning off the engine.

OK, the photo cleary shows the initial failure to be between 1 & 2.

But you are right to be suspicious about the very clean vales in cylinder No.1, especially if as it's the one now with low compression.

That kind of "clean" is often steam cleaning from a leak from the waterways.

The photo of the underside of the head perhaps shows other problems - those brass core plugs, I really hate but, as Andy says, it could be something as simple as the tappet clearance when you rebuilt it.

Schrödinger's cat - so which one am I ???

Okay - I'll reset the tappets and see how that goes when I'm looking at it tomorrow.
Thanks for the suggestions - all others welcome

Well, I checked the valve clearances - they were tight (around 0.2mm), so I reset them to 0.3. I made sure everything was connected/tight.... and no difference.
I re-tested the compression (engine warm) with the same result - 5 Bar-ish on No.1.
So next weekend I'll whip the head off and have another look (what should I be looking for?).
One thing I forgot to mention yesterday - there's quite a bit of vapour coming from the rocker cap/breather. Enough to put a film of oil on the rocker cover in that area - crankcase being pressurised?
Other than damage to the cylinder bore, is there any other signs of the piston rings having given up the ghost?

14 bar compression on an MPi?!.......... A little on the hight side? No?

looking at the valves this is no standard MPi................

I agree with Sprocket, that's not a standard MPI head, it's got a 36mm inlet fitted. It will be worth measuring the chamber volume to see if a lot's been skimmed off it.

Phil.

WWW.TURBO-MINI.COM

EVERY time a Mini head is off, it needs tone vacuum tested. At least remove the valves to see if the valve seats are fine on both the valve itself and the head.

Personally I like to try to find the reason for a head gasket failure before reassembly to make sure it doesnt happen again, is your ignition timing correct?

I seriously doubt it!

Blooming heck - there's some knowledge on here!
Phil, you must have bionic eyes! They are indeed 36mm inlets, standard size exhausts. Both waisted for better flow.
It has been skimmed quite a bit (hence the high compression Sprocket) - this was the first head I'd ported. I was aiming for around 10.7:1 - ended up around 11:1, so Super Unleaded only for me. I did have a problem with a blown head gasket shortly after fitting it (it was one of the dodgy Payen jobs). This last head gasket has lasted 30k+ miles, including 14,500 miles this last year (120 mile a day commute).
Vegard - it makes sense what you say. I should've stripped it down and looked at the valves and seats at least - lesson learnt! I've been thinking how I could achieve a vacuum test - now I've got my home made flow bench I should be able to utilise that in some way to see if there's a consistent seal (and now the wife has bought her own run around, I won't be reliant on getting the car up and running again! Ear-ache all this last week when I've nicked our other car, leaving her with the kids during the holidays ). At the very least I'll check the vales and seats/lap the valves in again.
Paul, being an MPi the timing isn't adjustable is it? Unless something severe has occurred.
I've started stripping the car down again tonight and noticed mayo in the crank breather/pipe that runs along the back of the rocker cover on the MPi. Can I just wash through the crank breather?
Anyway - thanks for the comments and ideas and help (what do they say about every day being a school day?). I'll let you know what occurs over the next few days.
Enjoy the Bank holiday!
Graham

Edited by Cooper1999 on 16th Apr, 2014.

Double post.

Edited by Cooper1999 on 16th Apr, 2014.

cracked ringlands, caused by the engine not being tuned for its increased compression and airflow. this also caused the gasket failure? what im getting at here, is perhaps you have two problems :(

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

I've seen a bogo standard MPi destroy a piston, see if I can find the pic.

Just checked my records - the head was fitted at 55k. The cars past 93k miles now, so nearer 40 thousand miles, not 30.
Give your comment on a standard MPi piston Sprocket, perhaps I've got a good'un! Is that another example of Rover cost cutting and lowering quality standards?
This is the mayo in the crank breather:

With the head off this is what I found:
Bores look good (no. 1 shown):

No1 & 2:

No3 & 4:

Am I right in thinking, ideally you want the piston to meet the block deck height for good power production? I seem to remember reading this in Vizard?

Not the clearest of pictures, but this is the back of No.1 valves:

And the chamber:

One thing I did notice when removing the head was, the head stud (No.1 in the Haynes manual) came out with the nut. I ended up removing it from the head with a stud extractor. I don't know if the stud extractor damaged the thread, or whether I've damaged it when I last put the head on (I do normally wipe/check threads before assembly, honest!).
Turning the engine over with the head off, it turns over beautifully smoothly and easily.
evolution - the two problems being a broken piston and too much compression for the spec of engine?

ETA - Forgot to ask, what am I looking for regarding possible cracked water jacket? Where should I be looking, what am I looking for? Is there anything in the photo's that suggest a problem, or am I resigned to pulling the engine and stripping further?

Thanks again.

Edited by Cooper1999 on 19th Apr, 2014.

How do you know you have a goodun if you havnt pulled the pistons? Id have done a leak down before pulling the head to see where the compression in that cylinder is going:/ if the valves were seating ok, block and head were flat and no cracks can be found im afraid your going to have to pop a piston or two.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

I'd want to say the head has a hairline cracking in one of the inlet ports causing it to burn a small amount off coolent.

Do you have a standard head you could try?

13.95 1/4 mile on a 2.95 fd. Carnt be that hard to beat!

Piston no 3 looks like it may have some damage to the crown. It may well be the pics/reflections.

Get it up to the top of the deck and have a look.

In the 13's at last!.. Just

Mayo in the breathers is not uncommon. I'd be more concerned if there was Mayo in the rocker cover. Has the cooling system been over pressurising? does your expansion tank look stressed at all? those are indicators of combustion gasses entering the cooling system.

You could try a vac test on the cylinder. I'd try a little oil around the top ring land, and with a thick piece of prespex, drill a hole in the center of it and connect up a Mityvac or something else, like a Laser evacuation pump (available from Machinemart). Seal the perspex onto the block above the cylinder with some sort of putty, plastecene or bluetack and then draw a vacuum and watch what happens around the rings. There should be a fair resistance and only a little bubbling of the oil around the top ring if at all.

It might be time to pull it appart and have a looksie see.

Edited by Sprocket on 19th Apr, 2014.

Thanks for all the comments guys - I appreciate your thoughts.
eden - I have this head which is a similar spec to the head already on the car (36mm inlets, standard size exhausts) which hasn't yet been skimmed. A light skim to make sure it's true should give it a compression nearer to the standard 10.3:1, and allow me to use normal unleaded (thereby saving a few pennies. Then again, with the missus having her own run around and me having the use of another car/bike, the mini won't be doing so many miles now):

I also have a totally standard MPi head on this which I could use:

The engine in the MM was going to be my first attempt at a full engine build so I've already got a pile of bits assembled ready for that (which would've brought it's own set of questions ). I guess I just thought the mini would carry on with routine maintenance, it's proved pretty damn reliable in the 11 years I've owned it (which includes the odd track session, flat out autobahn runs and as mentioned many years doing between 6k and 14.5k in commuting).
evolution - I meant the engine must've been pretty good on 'Rover' assembly (before this recent problem) if some have broken pistons when in a standard state of tune.
theoneeyedlizard - having had another look at No. 3, I think it is reflection in the picture as it looks pretty much as per N0. 2 & 3 by eye.
Sprocket, I have Perspex available so I'll give your idea a go tomorrow (family day today - hope you're all making the most of a sunny Bank Holiday too!). I may be able to make use of the vacuum box from the flow bench to give enough 'pull':

If I do end up pulling the engine, it would give an opportunity to sort the crunchy 2nd gear I suppose.
ETA - The header tank looks fine, and I've never had any problems with overheating, or loss of coolant.

Edited by Cooper1999 on 20th Apr, 2014.

Well, started the day with this:

Ended the day like this:

I stated by stripping down the head (valves now pickling in vinegar to help clean them up) and couldn't find any sign of a crack. I did notice some marks on the top of the stem on a couple of the valves though (not sure if this will show up in the photo):

Moving on to the block I can't see anything out of order there either. Moving on, I made a Perspex panel and, nicking some playdo and the missus' hoover, I tried Sprocket's vacuum test. I wasn't sure the hoover would be up to it but actually it worked quite well. There was some bubbling in 2,3 & 4, but No. 1 was worse. I undertook the test a couple of times to be certain, but what truly convinced me was, after a cup of tea, the gap around N0. 1 piston was drained - No. 2, 3 & 4 still held oil. Not scientific, I know, but with the long weekend almost over, the engine was coming out.
So, the next thing to do is attack the search button, I think. I've got a copy of the Ultimate Mini Builder engine DVD. Time to watch that again I think. And I have a rebuilt gearbox (which was earmarked for the MM) fitted with a 2.9 diff (how would a 3.1 diff do in a daily? Would give the MPi a bit more get up and go!).
But before I go and finish this thread just a few more questions if I can:
If only one piston has gone, am I okay changing just that one with a standard piston (as opposed to re-boring at the next size and replacing all)?
Do I need to have the crank reground, or just measure it and get some new shell bearings?

Thanks again for the advice!

Not the best of pics but:


Cracked piston in between the ring lands:

Thanks for the help- I just hope I can get this all back together correctly:

Time for some JB Weld.

:( least u know!

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.