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1275 Build Concerns


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#1 super6al

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Posted 21 November 2020 - 08:44 PM

Hi everyone.

My long running engine rebuild is on again :shy:  and I have a few issues. Its a 1990 1275 Rsp cooper with the original 12A MG metro engine. I've kept it standard as bores & pistons are fine but I'm fitting new bearings & rings as part of a complete stripdown & overhaul due to an earlier gearbox problem.

So... 

1) I gapped the new rings today but I'm finding variation, especially with the second ring (although top rings may have the same problem as Ive only measured 1 of these so far). They are Grant rings made in the USA & are supplied in separate packets for 1, 2 & oil control.

  I set the middle rings 2.5 inches down no.1 bore using a piston to set them square. I also confirmed using a vernier to measure the depth. Of the 4 rings in the set one is bottom spec (8 thou), one is top spec (13 thou), however the other two are measuring at 18 thou. I've tried the ones with the 18 thou gap in no.2 bore with the same result. As a further check I set them 5 mm down the bore above the ring land & they measured 17.5 thou. Are these two ok to use?

2) Crank end float. I measured this using a dial gauge on the end of the crank & measured it at 3.5 thou. I thought this was ok, however the Haynes manual says 2~3 for the 12A engine so I tried a set of +3 thou washers but the crank was tight to turn by hand. So I reverted back to my original standard washers. Again is 3.5 thou ok?

3) Following AndyMiniMad excellent rebuild guide on this forum, Andy oiled the back of the main bearings before installing, however a couple of people advised against this & suggested installing them on a cleaned surface stating 'the bearing could possibly spin'. Unless I've missed something its not possible with mini shells as the opposing tangs will prevent this. Are there any other reasons not to oil them?  

Thanks

Alan 



#2 RooBoonix

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Posted 21 November 2020 - 10:40 PM

Hi everyone.

My long running engine rebuild is on again :shy:  and I have a few issues. Its a 1990 1275 Rsp cooper with the original 12A MG metro engine. I've kept it standard as bores & pistons are fine but I'm fitting new bearings & rings as part of a complete stripdown & overhaul due to an earlier gearbox problem.

So... 

1) I gapped the new rings today but I'm finding variation, especially with the second ring (although top rings may have the same problem as Ive only measured 1 of these so far). They are Grant rings made in the USA & are supplied in separate packets for 1, 2 & oil control.

  I set the middle rings 2.5 inches down no.1 bore using a piston to set them square. I also confirmed using a vernier to measure the depth. Of the 4 rings in the set one is bottom spec (8 thou), one is top spec (13 thou), however the other two are measuring at 18 thou. I've tried the ones with the 18 thou gap in no.2 bore with the same result. As a further check I set them 5 mm down the bore above the ring land & they measured 17.5 thou. Are these two ok to use?

2) Crank end float. I measured this using a dial gauge on the end of the crank & measured it at 3.5 thou. I thought this was ok, however the Haynes manual says 2~3 for the 12A engine so I tried a set of +3 thou washers but the crank was tight to turn by hand. So I reverted back to my original standard washers. Again is 3.5 thou ok?

3) Following AndyMiniMad excellent rebuild guide on this forum, Andy oiled the back of the main bearings before installing, however a couple of people advised against this & suggested installing them on a cleaned surface stating 'the bearing could possibly spin'. Unless I've missed something its not possible with mini shells as the opposing tangs will prevent this. Are there any other reasons not to oil them?  

Thanks

Alan 

 

Here's my 2 cents..

 

1) I wouldn't be too worried, too tight is worse than too big. 18 thou, whilst out of "spec" wouldn't cause an issue imo

 

2) Have you tried mixing thrust washers from the set of +3 and your originals, to perhaps make a set of ~+1.5 thrusts?

 

3) I oiled mine, it's preference, just a smear with a normally already oily finger. The tangs mean the bearings shouldn't spin, they're present in alot of engines. But in my mind, if a bearing wants to spin, it'll spin, oiled backing or not.

 

 

Hopefully you'll get some more opinions on here too and you can make an educated decision for all your points, good luck with your build



#3 Moke Spider

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Posted 21 November 2020 - 11:54 PM

The Ring Gaps are fine. I think there's too much emphasis put on getting these 'just right' when in reality, as ling as you have 18 thou and up to about 24 thou, you are fine. I know many go to extremes to get these as sensibly tight as they can, however back to back Dyno testing has shown this to make no difference.

 

I never set the end float at anything less than 0.004". I know what the books say and frankly, it's just too tight for my liking. ACL (Bearing Manufacturer) recommend for a 2" Main Bearing, the end float should be 0.004 to 0.006".

 

Never oil the backs of the bearing shells. They should be totally dry. I use thinners to clean the shells and the caps before fitting the shells. You need maximum metal to metal contact so that they shells don't spin and also for heat transfer.



#4 Cooperman

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Posted 22 November 2020 - 12:27 AM

I'm with Chris, but I work on nominal 0.003" to 0.005" for crank end float on a new build. I will accept 0.0025" as an absolute minimum though.

Ring gaps are fine.

Fit bearing shells into clean housings with no oil present.



#5 RooBoonix

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Posted 22 November 2020 - 12:51 PM

Looks like I'll be fitting mine clean and dry next build, can't argue with the guys above. Heat transfer isn't something I'd considered.

#6 super6al

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Posted 22 November 2020 - 01:11 PM

One more item if I may - I have removed the rivet & blanking plug in the block & replaced them with grub screws, however I have now found another rivet lurking in the head. Is it good practise to replace this also or just leave it?

Thanks everyone for the help with the 3 issues in the first post - gives me the confidence to carry on - brilliant forum as always.

Cheers Alan



#7 cal844

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Posted 22 November 2020 - 03:53 PM

You can replace it with the grub screw method, however if it doesn't leak don't change it.

Just my 2p

#8 Moke Spider

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Posted 22 November 2020 - 05:33 PM

On every rebuild, I pull the Plugs from the Main Oil Gallery in the Block and the one in the Head that you've mentioned here. I also pull the Oil Pressure Relief Valve Seat and all the Freeze Plugs, then after these plugs are out, I send the block out for chemical cleaning.

 

The Main Gallery Plugs, I replace with M14 Cup Point Grub Screws and that in the Head with a 5/16" UNF of the same type. I use that mix of sizes as the drillings that are already present readily accept the sizes for tapping.

 

There are other Plugs that can (and possibly should be) Pulled as well, but as these are in the return oil path or pre-filter side of the Oil Circuit, I make a judgement call on those, if the block is particularly grubby from burn or old oil or rusty, then I pull them too.



#9 super6al

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Posted 22 November 2020 - 06:39 PM

Thanks cal844 & Moke.

On reflection I think I'll replace it with a grub screw. I previously removed all the oil & freeze plugs in the block & did my own hot caustic solution wash (inc. the head), which was quite good at removing a lot of crud. I hadn't considered replacing the gallery plugs with grub screws as I intended to fit new knock in plugs but will give this some thought as I can see the advantages.

Alan



#10 Moke Spider

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Posted 22 November 2020 - 07:16 PM

 I hadn't considered replacing the gallery plugs with grub screws as I intended to fit new knock in plugs but will give this some thought as I can see the advantages.

Alan

 

If you don't see yourself pulling it down again, press in plugs are quite OK.

Be it Grub Screws or Plugs, I fit them with a dab of Loctite to seal them.



#11 super6al

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Posted 22 November 2020 - 09:41 PM

If you don't see yourself pulling it down again, press in plugs are quite OK.

I'll be gutted if I have to   :D






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