1275 rebuild

[RichardG]

Hi,

I have stripped my new/old 1275 engine and to the best of my ability with limited measuring equipment chaecked various clearances etc. Nothing is perfect but as far as I can tell most things are just within tolerances so it seems like I can get away without any major expense for now.

I am putting in new main and big end bearings and was going to put in a new set of piston rings but I found out that they are not availble any more for the pistons I have (Hepolite 20142, its an Alegro block !)

So my question - would it be a good idea to do a very gentle hone / de-glaze on the cylinders given I am re-using the original pistons & rings ? If I was putting in new rings it would definitely need a de-glaze / hone. The reason I ask is that one of the cylinder bores has some brown discoloration and and a vey slight ridge where I guess at some point the piston was sat for a while with a little moisture in the cylinder. A quick run up and down with the hone would probably clean it p, but I am not sure it is a good idea ??

Richard

 

[Mini Mad Max]

Hi richard,
Brown discoloration is just oil stains, i had it before i had a hone. The only reasion why i think you should have a full hone and new rings (which aren't cheap at £80 for a set! ) is that you say there is a slight ridge. If you can feel it with a finger nail then it's not a good idea to leave it. If it's just a mark then that's ok. A quick gentle hone in the bores are good for attracting oil onto the bores which it wouldn't if it's all polished from the pistons. To do this you may have some wierd device or just gently swirl some wet and dry paper in the bores, very gently though, you don't want to affect compression.
Max

 

[esdebe]

If you re-hone then you will need new rings, the hone allows the rings to bed in properly, and as they bed in they lose the sharp edge they come with, if you hone and use old rings you will probably end up with reduced compression and oil coming through. 

Did you do a compression test before hand, if so and everything was OK don't do anything else.  Saying that when I was putting my old pistons and rings back in once I managed to smash the ring when it popped out the end of the compression tool....  If you can 't get new rings for your pistons you will need to take extra care as the older the rings get the more brittle they got too...

 

[RichardG]

Hi - thanks for the input I decided not to hone as I did not want to compromise the old piston rings. I did however clean up the marks on the one piston bore by gently rubbing with some fine grit paper, turns out it was just some light surface rust where the piston had been sat for a while.

Engine is now back together and in the buggy ready for a trial next weekend.

Its a 1275 allegro block with std pistons etc. MG metro turbo cylinder head that has been nicely ported with big valves. Head has been skimmed and 2.5mm removed which I guess increases the compression ratio. Camshaft is from an MG Metro so has better lift/duration that the std mini 1275 cam.

Seem to have got the engine running nicely but idle is a bit high (1100 rpm) does this sound reasonable?

The only issue I have is "run on" when the ignition is switched off the engine runs on for 3-4 seconds. The timing is OK and there is no pinking under load. Spark plugs are a nice colour so I think the fuel mix is OK.

I have heard that the MG Metro was fitted with an anti run on valve ? anyone else had the same issue?

Richard

 

[Mini Mad Max]

I seem to recall a handful of people on here when i spoke to them at stoneleigh had provblems with running on. My dad used to get it all the time in his mini, I don't think an anti run on valve is particularly expensive either, i may be wrong though
Max