Found some old ring fitting instructions and the figures it gives for compression ring gap clearances are a min of 0.003" (3 thou) per inch of bore diameter and a max of 0.010" (10 thou) per inch of bore diameter. It also goes on to say that maximum ring gap is not especially critical but ideally shouldn't exceed the 0.010" per inch figure. For oil rings it can be up to 0.070" (70 thou) regardless of bore size.

Also make sure that the gaps on each ring are not all in line with each other. eg: for a 3 ring piston set them at say 120 deg apart.
The most important thing is to make sure the gap is at least the minimum otherwise you risk the ring gap closing up when the engine is at operating temp and that could spell EXPENSIVE.

Be aware that there are so called gapless rings around as well and that's a whole new ball game.

Generally if the tapered edge is on the outside of the ring the taper should have the largest diameter toward the bottom so that you get the oil scraping action.

Edit:Other ring types have a chamfered edge on the inside diameter and this should be at the top. The idea here is that compression gas can get behind the ring and press the ring face against the cylinder. This type usually has a parallel face against the cylinder wall.

However all rings are not created equal and the ring set may have different compression ring types for each groove in the piston.
You really need to refer to the instructions that should have come with the ring set. Failing that you need to talk to the blokes that supplied the rings.

You also need to be surgically clean when assembling everything as just one tiny spec of grit can cause problems.
Make sure you clean the bores until you can wipe a clean cloth around the bore and not pick up any colour on a white cloth. Honing grit left on the honed surface will continue the honing process when the engine is running. Not a good idea.
Edit: Clean the bores with hot soapy water and a scrubbing brush and then lightly oil the bore and do the white cloth wipe test and repeat as many times as necessary.

Hope this helps to set your mind at rest
RonR

Re the detonation damage to the piston.
I had the same issue with a MK2 engine I aquired and it turned out to be due to a bent distributor shaft. The ignition timing is usually set using No1 cylinder as a reference for all the others but if the dist shaft is not straight then the ignition timing for the other cylinders won't be correct. In my case the car had had a bingle in the front and the dist must have been hit and the shaft got bent. The Aussie 29D4 distributor has a particularly long length of unsupported shaft where the point cam is and is easily bent. Make sure you check that the shaft is not bent or your best engine rebuild will end in another detonation disaster.

RonR

When you go to fit the crank, make sure you have plenty of clearance between the crank shaft thrust faces & the "LOWER" half thrust washers on the main cap.

In other words make it take all the thrust loading on the Upper thrusts (block) so the crank flex/whip/distortion doesn`t push on the main cap & make it wobble

By Allowing the main cap thrusts (the lower pair) lots & lots of clearance, helps stop major problems there. Especially if you`re going to rev it. hence peoples continued insistance in using steel main caps & main cap straps & 4 bolt this & 4 bolt that & & & etc etc etc,,, not saying that`s all crap, just saying that a little extra clearance (like 10 tho extra) for the main cap thrusts will save a major head ache & lots of money later on when you rev it hard.

& if anyone doesn`t agree with me then go suck eggs

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

My 2 bob worth: To thin thrust washers, lay fine grade wet/dry on a piece of glass, lube it up (GR uses deisel) and file away until desired clearance is achieved. Check the trust washer is totally flat at different locations along the washer, esp if it is s/h and esp where the number is stamped which can be 1 or 2 thou thicker than the rest of the washer.

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Lillee - 1969 Morris Mini K

My 2 bob's worth-
I use .007" endfloat on both my 1360 and 1412. This is the same clearance as GR uses for revvy 1275s..
.003" as per the book is NOT enough, as I found out the hard way.

I have to thin the std washers by over .016" each, because I'm using an EN40B S crank in a Morris 1300 auto block. There is 1/32" difference in centre main journal width.
But my friendly toolmaker and his surface grinder are just down the road, no problem.

Putting an 1100S crank into an S block gives the opposite problem- you need +.030" thrust washers. These are now NLA from UK, but ACL still makes them out here. I bought some, just in case...

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Hey if your engine was stress plate honed then the cold bore size will be all over the shot so careful with setting your ring gap off the bore!

Also put some healthy chamfers on the head stud holes and drill out the top 5mm of thread. Sounds crazy but when I saw the picture (FEA) of a skyline block under load the area around the stud holes was raised it became as clear as day. Clamping load distribution gets better with a good chamfer and lower engagement.

I was talking to a Dr. of metallurgy in the fastener industry and was told a structural grade (PC8.8) bolt takes 80% of its load on the first 3 treads at correct pretension. This also falls inline with the cone pull style of the skyline picture.

On performance engines I use to stress plate (60mm thick) hone at 27 celcius and get cold ovality of over a thou. The hone stones are used in 2 grits, the rough forms the oil catching grid in the bore and will be all thats left after 1000klm, the fine grit over the top of the course is to bed in the rings and polish off to form the plateau for ring support. From the pics it looks like you have a high revving grid pattern, hope thats what you wanted.

Finally wash your bores with hot soapy water **do not use detergent as a base** the cast iron dust that gets stuck in the hone grid is amazing in its quantity and engine destroying ability.

Good Luck.

Mick

How did you hot dip the block at home?

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David L


My greatest fear in life is that when I die my wife will sell my Mini and tools for the price I told her I paid for them!

Wow, heaps of reading there, and all good too. I just finished putting the rings on and the right way around, and this stuff all preempts of the next job of putting in the crank.

1. So what I pick up is regardless of the quality of the clearance around the thrust bearings on the center cap, polish a few thou off the cap's pair of thrust bearings to make sure the block cops it most. This would mean the bearing cap thrustys are just hanging in there for the ride. Does this accelerate wear on these parts?

2. I've had it pointed out that I should find a use for plastigauge while fitting the crank. I can forsee checking thrust clearances with a feeler gauge, what operations should I also be performing to need plastigauge?

3. Are there any operations I should be performing on the journal bearings to check for correct fitment and clearance? Or do we generally trust they will be fine once fitted?

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Mick, the only true and proper means of checking endfloat (thrust washer clearance) is with a dial gauge on end of crank, using feelers is not accurate enough really. Although at least with feelers, it'll have more clearance than you measure.
Just don't make em too tight if you're going to rev it. 1275 cranks flex heaps.
When I stripped my 1360 that nearly spun the centre main bearing at Wakefield Pk, I found circular `fish scales' of bronze thrust washer sitting in the bottom. And that crank was fitted with the factory recommended .003" endfloat.
It's got .007" this time.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Dial gauge and magnetic mount is on their way from Queensland (thanks to my brother). I should have it towards the end of the week.

Just fiddling around, I put in the main bearings and crank tonight. With no way to check the end float it will have to wait to be torqued up. With the old nuts holding down the caps at a light torque, I can turn the crank with two fingers easily enough.

What the best sort of locking/non-locking nuts to use on the main bearing studs? I have the old single use locking type nuts but won't use them again obviously. An engine I rebuilt years ago used "Unilock" nuts I bought from a nut/bolt retailer. I suppose I should use hardened washers here as well under the nuts, correct? Any recommendations?

I have new ARP big end bolts for the rods, so they're covered.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

I used a pot of caustic soda flakes I picked up from Bunnings. Mixed it into a large tub of hot water and put my bits into there. The paint produces light bubbles and turns to crayon in half a day. The hotter you can keep the water the faster it will work, but not having a heater I left the tank in the sun to keep it warm for longer. It worked well. 10 percent is the mixture I am told to use if you can work it out.

I then blasted everything with a high pressure sprayer and detergent before oiling it up.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Nice block you have there,,, thick flange,,, no hole above centre main, , , MK2 "S" ???

edit--> oops sorry , just re-read your very first post & you allready said it was MK2"S", I`ll say it again tho--> nice block

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

sure is.

You must have had a few pass through your fingers as well matt..and kept a few as well?

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

re the main bearing nuts- if threads are all good I would just oil the threads and under the nuts, and torque up to 60-65 lb/ft.
It's the stud stretch which keeps `em tight. Same deal with main bolts in other 1275s.

Some people (including me, once) put Loctite 262 or similar on the dry threads. But these days I oil them as said above.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

OK, so plain nuts and loctite then. I'll buy 6 new ones for good measure. These old ones seem to bind, and then not, and then bind which surely cannot be a good thing.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.