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Hi!

I´ve bought what seems to be a really well built 970-engine. I´m about to dismantle it to check it over, but prior to this, I need some of you true experts to help me out, since I´ve never fiddled with a 970 before

The crank seems to be the original S-crank, stamped EN40B, so hopefully no probs there.

But - the rods are AEG521 (from a 1275/1071), shouldn´t they be to short for the 970? Can´t imagine they´ve shaved the extra .075 (or something) off the block to compensate. The person I bought it from was led to believe that there were "off-set pistons" installed. The pistons are Omega, seem to have very short skirts, stamped P304.

Anyone heard of this technique? Basically letting the pistons create the extra height needed instead of the rods... The block height is 219 mm or 8 3/5" approx. That´s 6 mm or approx 1/4" lower than my 1275 S block, however I don´t know if that´s been machined sometime in the past, too.

The engine also has a Calver belt drive. I´ve never heard of it, I´m afraid. Does anyone know if it´s any good?

Since it all works, the engine has been run, why not leave it as it is? Well, AppK doesn´t allow the use of A+-blocks, so if the engine is to be used in racing, I need to change the block for a non-A+. I don´t know if an A-block can be converted with the same success as this A+ has. And since it´s a fair amount of maching involved, I need to know what I´m doing, before I do it

So, basically; can I use the parts in this block and convert an A-block into the same type of engine instead? Or this is a one-off somehow? If I can´t convert it, I´m stuck with a lot good parts of absolutely no use to me

I´ve attached some photos.

ive got a couple of engines using chopped down a series blocks and SA 1071 cranks, with no issues

Didnt someone mention that 521 rods were availbable as both 1275- or 970 length?

thx, this is what I can´t figure out; if my 970 uses the same rods as your 1071 engine, then my engine must compensate for the loss in "piston height" some other way. From what I´ve learned the 970 blocks couldn´t be decked further by the factory when built, and therefore needed special rods to compensate. This engine doesn´t use the 970 rods...

Do you think you can check the block height of your 1071`s so we can compare? I hope that my engine somehow compensates the height by special pistons instead of "over-decking". I think there´s an approx 2 mm difference in rod length, or .075", between 970 rods and the others. I just don´t think any block can take that extra decking (instead of using the right rods), it would mean shaving off 1/3" instead of already suspiciously daring 1/4".

Have you or anyone else heard of special pistons for the 970?

Thx for reply, looking forward to solve this

Regards

Stefan

Edit: Saw your reply, Sandman. Takk. That would be a very pleasant explanation and one I wasn´t aware of. Isn´t that be BMC-ish, same part number, different parts Seems indeed like the 970 and1071/1275 rods share part number and have to be measured to see which is which.

If anyone can confirm what the deck height is for an original 970-block, then all is good. It would mean I have a complete 970-setup (no "off-set pistons") and only have to change the block

ive had a few s blocks that had been decked to suit a 970 crank running std length 1275/1071 rods - from the days when autograss had a class limit size and the cranks where easier to find than the rods.

they do skim down to this height with no problems, the problems are that they then have a very, very limited market as no body really wants a s blocked thats been skimmed so far.

once the grassing engine size changed to 1130, they all scurried back to 1071 cranks and had to reblock the engines as the 1071 crank/rod combo poked the pistons out the top of the block.

these are all from the days prior to fancy steel rods and short deck pistons, they could probably be used now, but i think i weighed them all in for scrap

so that´s where all the blocks went well, times have changed and not too many are seen weighing in S-blocks for scrap anymore, I guess...

Anyway, the S-blocks were a different casting and what was on the limit in terms of decking the S-block would be, I guess, impossible on an ordinary A-block. I do have a very tired 1275 S-block, though, and if I have the correct rods, it seems I could machine that block and put together an original spec 970 engine.

Thank you for sharing your knowledge. Now I just need to know the original height of a 970-block. Well, and maybe the name of a good machine shop in the UK that can modify the block, including line-boring etc. We have a few good ones over here in Sweden as well, but I guess it´s well worth paying the extra £££´s for the experience gained in the UK over the decades with these engines.

The block " thickness " on a standard unmachined 1071/970 block is 218.36mm ( 8.597" )

Con rod centres on a 970 rod is 149.23mm ( 5.875" ) AEG 177

Con rod centres on a 1071 / 1275 rod is 146.05 ( 5.750" ) AEG 521

You can get 970 rods made from AEG 521 forgings , ask vegard

251 ENG wrote:You can get 970 rods made from AEG 521 forgings , ask vegard

Indeed... Crap

Get som custom rods, or 970 length H profile rods, fit this to an A- series block and be done with it. Easy!!

guru_1071 wrote: once the grassing engine size changed to 1130, they all scurried back to 1071 cranks and had to reblock the engines as the 1071 crank/rod combo poked the pistons out the top of the block.

Yup, I bought such a short motor recently with a nice 1071 crank in it to replace my doorstop and it was in a much skimmed down GT block. Quite scary looking at how much deck there is left when these were shaved down !

thx all for sharing your knowledge, now it all makes sense, just didn´t know about the rods being "same but different"... since the height of my block is the same as that of an original 970, it seems like the engine does have the correct 970 rods. Only other solution would be special pistons, but since noone seems to have heard of "970-pistons" (and Omega doesn´t mention it anywhere), I understand this as it has to be a correctly built 970 with the longer rods.

Definitely makes it worthwhile preparing the correct block for this engine, then, so it complies with AppK.

Moneywise, does an S 970 have about the same value as an S 1275? Just wondering, since I intend to mill down the 1275 S-block I have. Would that be - not so wise

i would say that a std height 1275s block would have a greater value than a 970 / 1071 height block

You could fit these, cough cough;)

http://www.7ent.com/products/pauter-for ... 9-set.html

I would......

JCWorks wrote: Definitely makes it worthwhile preparing the correct block for this engine, then, so it complies with AppK.

Moneywise, does an S 970 have about the same value as an S 1275? Just wondering, since I intend to mill down the 1275 S-block I have. Would that be - not so wise

I didn't think you needed an 'S' block anymore for App K ? Better to flog the 1275 S block and that should pay for a correctly decked and bored GT block ?

Correct, they (wisely) allow the use of ordinary A-blocks now, not A+, though. But since I have an S-block that needs a lot of maching to be servicable anyway, I´m considering using that, hence my question about the value. But as you say, it seems the best would be to modify an ordinary A-block, I have an MG1300-block, and leave the S-block as it is for future use.

Is there a way of measuring the deck height to see if an ordinary A-block can be sufficiently shaved? Without really knowing, it seems it works sometimes and sometimes not, indicating that the A-blocks castings differ over time.

Vegard: 6" inch rods would solve the problem in no time, unfortunately coming up with $1100 would take a little longer

And I´m not sure 6" rods would comply with AppK... so it´s back to square one.

The rods will not comply with App. K, but seriously... Who will know?
So you will rev to 9000rpm with 50 year old rods... I'd look hard for $1100 instead....

You'd also run a thicker deck with these making the setup much more reliable, and allow for future decking. It's a no brainer

Here is a spare std bore block I have laying around that had been decked:

JCWorks wrote: Is there a way of measuring the deck height to see if an ordinary A-block can be sufficiently shaved? Without really knowing, it seems it works sometimes and sometimes not, indicating that the A-blocks castings differ over time.

ive got two engines running decked a series blocks (i.e to suit a 1071 stroke crank), and another currently being built, there is tons of meat left on the face of the block.

i know of literally 100 plus people who have decked blocks like this and have never, ever heard of water ways breaking through or stud holes bottoming out.

there was someone on minifinty / tmf who was adament that 1275 blocks couldnt be chopped, but when i gripped him about he admited that he had never done, or actually ever head of anyone doing and having probelms....

Looks good, by eye it still seems to have a fair amount of thickness left. Interesting, since I´ve heard there´s a possibility of making the blocks unserviceable when decking this much. Where are the most critical points on the block? Is that a GT/MG1300-block?

Longer rods is a good idea, technically, bringing the advantages you mention, Vegard, the extra thickness is indeed very welcome. But it´s easily detected, a steel ruler to measure the block height would reveal it in no time and all of a sudden the $1100 spent would seem to be less of a good idea. Besides, it just wouldn´t be fair. I know there´s a lot of "on-the-limit" solutions in classic racing, and challenging the regulations is almost part of the fun with bent tie-rods etc. But it still would be against regulations...

But from the technical point of view, I do agree, and it makes me think twice when you write "So you will rev to 9000rpm with 50 year old rods". You make it sound a little scary

On the other hand, none of us first looked on the Mini thinking "well, that looks like a reliable piece of machinery", did we

Original rods it is, then

EDIT: thanks guru_1071, that´s the info I´m looking for. Hands-on experience. Conclusion: I can skim the MG1300 block. So be it, let´s hope for a long, cold winter up here so I can finish the engine before next season.

Who can recommend a good machine shop in the UK to do the work on the block?