307 replies to this topic

[davej]

Right its time for an update, I haven`t done much recently apart from trying to enjoy driving the mini when the weather has been nice. After 500 miles she`s still smoking once the oil gets warm I couldn't carry on driving it so I've taken the head off to do some investigating.



After a closer look I noticed that cylinder no 2 is oval, I can get a 0.7mm feeler down the right hand side of it, surely that's far too big of a gap??



Dad is bringing home an inside micrometer home so we can measure the bores and go from there.

Cheers

Dave

[davej]

We have measured all the bores and they seem fine so then we had a look at the head and I think we have found the problem.

I bought a big kit off swiftune with double valve springs in but no locating washer for the inner spring so that could be an issue, also the valve stem seals that came with the gasket set are pretty rubbish, I can slide with valve through it without any resistance. When I took a few of the inlet valves out the stems were coated in oil from top to bottom. So the plan is to use single springs, new valve stem seals and might as well do the guides while we are it and hopefully that will sort out the old girls smoking habit.

Cheers

Dave

[Findlay94]

Youve done a really nice job here :) Starting my 91cooper project at the weekend!!!

[davej]

Thanks Findlay, I`ll keep an eye out for a thread on your project.

Well she lives again We`ve replaced the guides and seals, relapped all the valves in but no 3 inlet wouldn't seal so took it to a machine shop and they recut it. Built it all back up yesterday using single valve springs this time and got her running today, just need to tune the twin carbs and sort a small brake fluid leak out and we are back on the road.

I didn`t take many photos but here is one that shows how much crap was on the valves and this is after just 500 miles, gave everything a good clean before it went back in.



Another just showing the head built back up with single springs



Cheers

Dave

[Andrew O]

Good stuff, When will you be getting the head back on ?

Andrew.

[davej]

Its on mate I just haven`t got any photos of it back on, the engine runs great just need the carbs tuning.

[Andrew O]

Fair play to you
Well done

Andrew.

[davej]

Update time, not a good one though the engine is coming back out. Even after redoing the valve guides and seals she`s still burning a lot of oil and not running smooth, the only thing we can think of is oil rings. Going to start stripping it this week and I've got a nice new camera so I'll try to remember to take some photos. It's a shame but something is definitely not right and needs sorting.

Dave

[davej]

I have been busy in the garage today, started by dropping the coolant out, looks like its had a pee



Got it back in then got it up on ramps and axle stands. Then I started taking loads of stuff out: radiator, fan, alternator, starter motor and I've got the oil out and the filter and housing off.





I have some time in the afternoons this week so hope to have the engine out over the weekend at some point if all goes to plan.

Cheers

Dave

[davej]

I managed to get the cylinder head off today and this is what I found:



Lots of oil in the dish of the piston and smeared all over the side of the bores, I'm thinking its either oil scraper rings or the bores were oversized when machined. Surely I can`t have broken all the rings putting the pistons in? Time will tell as the engine is coming out over the weekend.

Cheers

Dave

[davej]

The engine is now out and split, all the rings look fine We are going to measure the bores properly tomorrow but I'm not so sure the they were over-sized as I've had 165 psi compression just before I stripped it. The pistons are the 21253 +20 one`s from minispares, as far as I can remember the rings came on the pistons, could they be the wrong ones or something silly like that. Running out of ideas at the moment. I'll get some photos up tomorrow.

[davej]

Well we've got to the bottom of it in the end, pistons are marked up as +20 but are actually standard size

Standard bore is 70.61mm so add the overbore it should be 71.118mm which is pretty much what we are getting with an internal micrometer.

Measured the skirt of the piston with a vernier and getting 70.12mm diameter.

[Andrew O]

Just to let you know I am reading all off this but I have nothing decent to contribute.
Hope you get it sorted ASAP.

Andrew.

[davej]

Cheers Andrew.

Does anyone know what the diameter of a +20 piston should be??

I think its about 71.004mm. Bore size is 71.118, maximum skirt clearance at the top of the piston is 0.114, take that from the bore size should be the piston size?

[davej]

Update time.

I took the block and the pistons to a local engine builder, the bores were to size as were the pistons. The bores were a bit glazed and the edges of the rings were sharp meaning its been running too rich and the fuel has washed away the oil and the rings have been metal to metal against the bores causing excessive wear to the rings (hence the 25 thou end gaps ). Thinking back the inlet manifold cracked when it first went on so we had to richen the mixture to get it to run, only when we knew something wasn't right and we took the carbs off did a piece of the manifold fall off. A new manifold was put on but the damage must of been done and we must of still had it a bit rich as I was trying to to run it in before putting it on a rolling road and I did not have a colour tune at the time.

They honed the bores but noticed some marks that you could feel where no2 compression rings stop at the top, sorted with a bit of wet and dry though, remeasured the bores with an internal micrometer and they are still fine thankfully. We have given everything a good clean and had the crank off today to make sure everything was clean and ok, put it back together and need to put the new rings on the pistons and put them in now. Hopefully will have some progress in the week and then if everything goes ok the engine will be back in next weekend fingers crossed.







Cheers

Dave