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 Posted: May 5, 2013 04:00AM
Total posts: 2421
Last post: Oct 25, 2014
Member since:Oct 8, 2011
US


I would think if he has the midget/sprite engine he should have the rods. I have a large collection of sprite rods, Cooper S rods and a new set of A+ rods. I have some race preped A+ rods lightened balanced and floated. Steve (CTR)

 Posted: May 3, 2013 08:16AM
Total posts: 2
Last post: May 3, 2013
Member since:May 2, 2013


Thanks for all the info.

 

 Posted: Sep 12, 2011 02:39PM
Total posts: 8187
Last post: Oct 21, 2014
Member since:Oct 27, 2000

If your 1505 crank is already ground down to 1.625" on the crankpins, the 1275A+ rods are not an option. You need either Sprite/Midget rods or Cooper S ones. Or, aftermarket race rods.

Kevin G

1360 power- Morris 1300 auto block, S crank & rods, Russell Engineering RE282 sprint cam, over 125HP at crank, 86.6HP at the wheels @7000+.

 Posted: Sep 11, 2011 09:25AM
mur
Total posts: 5089
Last post: Oct 19, 2014
Member since:Nov 12, 1999

Instead of narrowing the rods, have the crank journal widened when you go to the smaller size.  I also move the pin center-increase the stroke slightly- to bring the pistons to the deck of the block.  

This turns it into a very vast conversion:  One day with the crank at the machine shop, where chances are very good they do a superb job because it is so completely different.  Usually this results in perfect fillet radii.  Bring them the rear main cap so they can saw off the oil mover part.  Maybe take a 2nd rear main along so they can see what needs to be done.  This isn't a fancy job, it can be done with a mechanical hacksaw, just clean up all of the edges after.

 Posted: Sep 11, 2011 08:17AM
Total posts: 233
Last post: Oct 23, 2014
Member since:Mar 27, 2002
CA

Just a short update note regarding my conversion. I haven't done anything more since having a 12G1505 Mini Crank journals machined to 1.625". The next process is to tear down the rest of the engine so the rods ends can be narrowed to suit. Perhaps this winter I will get this done. Anyway, the only issue I see is the expense of the machining but I'm sure more hurdles are coming. The suggesting of using 1275 A+ connecting rods to avoid machining may be worth researching but that is not the direction I am going.

 

Cool

 Posted: Sep 11, 2011 05:33AM
Total posts: 36
Last post: Sep 11, 2013
Member since:Sep 17, 2010
US
I'm going to revive this thread as I have a question. I have a line on a fairly cheap midget 1275 motor, and am wondering how hard it would be to make it work in my mini. I've read the above posts saying it's pretty straight forward, but I've also read and heard from others that it's impossible, or at least not worth the effort. So i guess what I want to know is, is it worth it to convert a midget motor, or should I just search harder for a used mini/metro motor?

Also, Bobb I read that you've done this conversion a few times, what are your thoughts.

Thanks a bunch!

'Going to be 1275 mini!! '92 Sunburst Miata
 Posted: May 30, 2010 08:48AM
Total posts: 233
Last post: Oct 23, 2014
Member since:Mar 27, 2002
CA
Quote:
Originally Posted by Cup Cake

Probably Chichm.

Probably Chichm?  Do I need to know what this means?

Thanks for your offer Bob and others.  I do have a local machine shop that I have great trust in so good on this point.

 

Cool

 Posted: May 29, 2010 07:54AM
Total posts: 9547
Last post: Oct 25, 2014
Member since:May 13, 2001

Probably Chichm.

The power of keen observation is often viewed as cynicism by those who don't have it. G.B.S. Sarcasm is the lowest form of wit. Oscar Wild

 Posted: May 29, 2010 07:30AM
mur
Total posts: 5089
Last post: Oct 19, 2014
Member since:Nov 12, 1999

The left rear hub is threaded counter clockwise.

As stated above, the transverse crank has 1.75" connecting rod throws.  The inline engine came with 1.625" rods.  Also, the smaller rods are slightly wider.  This is OK, as stated above, for several good reasons the smaller pins are desired, and a good machinist can take an ugly 1.75" crank and turn it into a perfect 1.625" crank.  BOBB should be able to get your crank to a grinder who will understand what you need.

 Posted: May 28, 2010 10:27PM
Total posts: 8187
Last post: Oct 21, 2014
Member since:Oct 27, 2000

On all A series cranks whether inline or transverse, the pulley bolt turns CCW to undo. Bolt torque is 75lb/ft approx.
If real tight, either some gorilla has used a rattle gun to tighten it, or it's been Loctited (good idea, better than the current locktabs).
Rattle gun is OK for undoing, if necessary.

Kevin G

1360 power- Morris 1300 auto block, S crank & rods, Russell Engineering RE282 sprint cam, over 125HP at crank, 86.6HP at the wheels @7000+.

 Posted: May 28, 2010 10:24PM
Total posts: 3048
Last post: Aug 7, 2014
Member since:Jan 13, 2001

RON I'm 110 miles away in Kamloops and have done 3 of those so give me a call anytime if you need help. Bob B

 Posted: May 28, 2010 08:08PM
Total posts: 233
Last post: Oct 23, 2014
Member since:Mar 27, 2002
CA
Quote:
Originally Posted by Cheleker

There's only one fastener on a Mini that unscrews "backwards," and the crank pulley bolt is not it.

Actually this didn't answer my question.  The engine is a 1275 I think 1974 vintage out of a Sprite/Midget.  This is what I am removing the Crankshaft Pulley bolt from - not Mini.  I know the Mini bolts are CCW to remove.

Thanks,

Ron

 

Cool

 Posted: May 28, 2010 07:52PM
Total posts: 233
Last post: Oct 23, 2014
Member since:Mar 27, 2002
CA
Quote:
Originally Posted by Cheleker

There's only one fastener on a Mini that unscrews "backwards," and the crank pulley bolt is not it.

I appreciate this answer to my question now I am curious as to which one "unscrews backwards"? Left front?

Thanks,

Ron

 

Cool

 Posted: May 28, 2010 03:04PM
Total posts: 9528
Last post: Oct 20, 2014
Member since:Dec 3, 2002
US

There's only one fastener on a Mini that unscrews "backwards," and the crank pulley bolt is not it.

 Posted: May 28, 2010 12:35PM
Total posts: 233
Last post: Oct 23, 2014
Member since:Mar 27, 2002
CA
Quote:
Originally Posted by DRMINI

1275 Midgets (all? I think) had small journal rods, dimensionally the same as Cooper S ones.
The 12G1505 crank is a big journal one, 1.75" crankpins. Contrary to early popular belief, these are NOT `stronger' (ie resistant to cracking) than the earlier, small journal cranks. Crack test it first, before you do anything. Many here in Oz have cracks in, good only for doorstops.
A well known race engine builder here in Sydney always grinds them down to 1.625". His theory is they need some flex, or they will crack. IMO he may well be right...

As I said, if you don't grind the crank down, you will need big journal rods of some sort. I would use 1275A+ ones on a road engine.

Kevin,

I'm committed to doing this. I have the crank (partially ground) and Midget block.  I have been tugging on the Crank Pulley bolt but before I bust a gut is it CW or CCW to remove?  Remember we're in the northern hemisphere.  Also, you may want to correspond via email.  My address is tagusgreen@gmail.com.

Thanks,

Ron

 

Cool

 Posted: Mar 4, 2010 04:21PM
Total posts: 8187
Last post: Oct 21, 2014
Member since:Oct 27, 2000

1275 Midgets (all? I think) had small journal rods, dimensionally the same as Cooper S ones.
The 12G1505 crank is a big journal one, 1.75" crankpins. Contrary to early popular belief, these are NOT `stronger' (ie resistant to cracking) than the earlier, small journal cranks. Crack test it first, before you do anything. Many here in Oz have cracks in, good only for doorstops.
A well known race engine builder here in Sydney always grinds them down to 1.625". His theory is they need some flex, or they will crack. IMO he may well be right...

As I said, if you don't grind the crank down, you will need big journal rods of some sort. I would use 1275A+ ones on a road engine.

Kevin G

1360 power- Morris 1300 auto block, S crank & rods, Russell Engineering RE282 sprint cam, over 125HP at crank, 86.6HP at the wheels @7000+.

 Posted: Mar 4, 2010 07:42AM
Total posts: 233
Last post: Oct 23, 2014
Member since:Mar 27, 2002
CA

Kevin,

Thanks for this information. So I take it the existing connecting rods in the 1275 will not fit this crank without machining?

Ron

 

Cool

 Posted: Mar 4, 2010 12:25AM
 Edited:  Mar 4, 2010 12:30AM
Total posts: 8187
Last post: Oct 21, 2014
Member since:Oct 27, 2000

It's an easy job to fit it to a Mini. The bolt holes of the Sprite/Midget sump line up with a Mini or A/A box. I did this with a 1098 AH Sprite motor years ago.

Work needed:
1. Machine the return thread housing bottom half from the rear main cap.
2. Undo the return thread top half from the rear of block block and discard.
3. Unscrew and remove the oil Midget pickup pipe. On a 1098 Sprite the Mini O-ring seals OK to the block there, but check size. If the O-ring is too small to seal, screw a threaded bush in there and make flush.
4. Obtain a 1275 primary gear to fit your crank.
5. Cut the 2 engine mount wings off the front engine plate (not needed in a Mini).

[edit] Of course you need big journal rods to suit that crank, otherwise grind the crankpins down to 1.625" (stroke it too if you want) and use slightly narrowed 1275 Midget or Cooper S rods.

Kevin G

1360 power- Morris 1300 auto block, S crank & rods, Russell Engineering RE282 sprint cam, over 125HP at crank, 86.6HP at the wheels @7000+.

 Posted: Mar 3, 2010 09:45PM
Total posts: 233
Last post: Oct 23, 2014
Member since:Mar 27, 2002
CA

I know this has been discussed before.  I know of a 1275 Midget engine 12V/671Z and I have a crank 12G1505A.  Can someone enlighten me regarding the changes that would have to be made for this engine to work in a Mini. Oh and I also have a gearcase 22G1128 which used the remote shifter with rubber sandwich mount.

 

 

Cool