piston rings to tight
Discussion
hi i have just had a crank reconed and throught it a good idea to re ring it at the same time the problem is the rings that the machine shop have got me dont go in the bores
on the box of rings it says. R33646, STD, austin/morris, 2.7805"/70.625mm,
1.59+1.59+4.00. they will just not go in anyway. i have put a ring without piston in the bore and it looks ok but when its put on the piston it just will not go (yes i have used a ring compressor lol)
so do the numbers above relate to our engine a 1275cc mg metro
engine number 12HC14AA
10.5 : 1
Oct.1984- onwards MG Metro
thanks david
on the box of rings it says. R33646, STD, austin/morris, 2.7805"/70.625mm,
1.59+1.59+4.00. they will just not go in anyway. i have put a ring without piston in the bore and it looks ok but when its put on the piston it just will not go (yes i have used a ring compressor lol)
so do the numbers above relate to our engine a 1275cc mg metro
engine number 12HC14AA
10.5 : 1
Oct.1984- onwards MG Metro
thanks david
Check again the ring gap on each ring. You should have 0.003" gap for every 1" of bore diameter. Measure with fgeeler gauges. For a 1275 Mini you thus need 0.008" gap as a minimum. This is a must on every engine build.
Grease the piston in the area of the rings with wheel bearing type grease and just below the rings and also make sure that the top of each bore has a slight radius or a slight chamfer, say 0.010" or slightly more. Achieve this by using emery cloth and/or a fine file around the bore tops.
Put the piston into the bore so that the bottom ring is about 1" above the deck height. The tighten the ring compressor until it grips the piston firmly. Tap down on top of the piston woith the end of a 1/2 lb hammer handle. Do this lightly until the piston slips down the bore and you'll find the rings will just slip in without snapping. The secret is the grease and the setting of the clamp at the right amount of clamping force.
I know it's nerve racking as you are afraid of busting a ring (and we've all done that in the past), but use the right technique and all will be well.
P.S. When fitting new rings don't forget to lightly hone or otherwise 'glaze bust' the bores, or the new rings will never seat properly and the engine will lack compression and will smoke. I hope that does not sound patronising and you will almost certainly have done this already, but I have come across engines where that has not been done with subsequent problems which I've later been asked to sort out.
I hope all this helps.
Peter
Grease the piston in the area of the rings with wheel bearing type grease and just below the rings and also make sure that the top of each bore has a slight radius or a slight chamfer, say 0.010" or slightly more. Achieve this by using emery cloth and/or a fine file around the bore tops.
Put the piston into the bore so that the bottom ring is about 1" above the deck height. The tighten the ring compressor until it grips the piston firmly. Tap down on top of the piston woith the end of a 1/2 lb hammer handle. Do this lightly until the piston slips down the bore and you'll find the rings will just slip in without snapping. The secret is the grease and the setting of the clamp at the right amount of clamping force.
I know it's nerve racking as you are afraid of busting a ring (and we've all done that in the past), but use the right technique and all will be well.
P.S. When fitting new rings don't forget to lightly hone or otherwise 'glaze bust' the bores, or the new rings will never seat properly and the engine will lack compression and will smoke. I hope that does not sound patronising and you will almost certainly have done this already, but I have come across engines where that has not been done with subsequent problems which I've later been asked to sort out.
I hope all this helps.
Peter
The classic I had was a guy who had rebuilt an 850 engine, re-installed it, but was nervous about starting it for the first time. He asked me to go around to his place and check it all. It was all OK including the ignition timing, so I took the plugs out, spun it to get oil pressure, mput the plugs in and it started beautifully. He waved me to drve it forward out of the garage so I put it in gear, let the (new) clutch in slowly and it didn't move. I said "where is the bit that's left over?" and, sure enough, there on the back of the bench was the transfer gear! Still, it came out and came to pieces nice and easily!
I did feel sorry for the guy though so I helped him to put the gear in and put the engine back in again, which took about 8 hours altogether.
I did feel sorry for the guy though so I helped him to put the gear in and put the engine back in again, which took about 8 hours altogether.
engine nearly back togather so moved on to gearbox only to find a big piece of metal in the bottom of the box turns out to be half of the interlock spool so its strip the gears out now to get to it
now thats my problem i cant get the big nut undone on the 3rd ? shaft any ideas
or better still if some one would like the job of a rebuild please give me a price thanks
david
now thats my problem i cant get the big nut undone on the 3rd ? shaft any ideas
or better still if some one would like the job of a rebuild please give me a price thanks
david
On a related topic...
I'm coming up to the same stage in my build later, and was wondering about the rings.
When the old man puts new rings in, he checks the gap with no piston in and uses a file on the end of the ring to make any adjustments. He only works on old bikes, the last one of which had a CR of 5.5:1.
Would this technique be suitable for the Mini, or do I need something a little more specialised?
I'm coming up to the same stage in my build later, and was wondering about the rings.
When the old man puts new rings in, he checks the gap with no piston in and uses a file on the end of the ring to make any adjustments. He only works on old bikes, the last one of which had a CR of 5.5:1.
Would this technique be suitable for the Mini, or do I need something a little more specialised?
Modern pistons/rings are very accurate, usually.However, to be thorough you should check each and every ring by taking it off the piston, slipping it into the bore, pushing it down an inch or so using an old piston and checking the gap. It should be no less than 0.003" gap per inch of bore diameter, so about 0.008" or over is right for a Mini. If the gap is less just lightly file one end of the ring and make sure that there are no burrs after you do this. In fact, although I check every ring on every build, I can't remember when I last had to file to increase the gap.
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