Lotus Elan

701M L block question

PostPost by: patrics » Sun Jan 22, 2017 10:13 am

Hi,
On my original Stromberg headed engine one of the mains caps just fell in too when I stripped it down - so in my opinion definitely too weak for road or track.

Regards
Steve
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PostPost by: Chrisis » Sun Jan 22, 2017 5:45 pm

the Cyprus authorities they're looking for the right block that ford fitted on the escort. they gave me the option of either 681F L block or the 701M L block.

Because i'm not planning to have my twin cam as a garage queen and i will involve into some racing the only way for me is the 701M block.

I'm 34 and i don't want to think too much into rarity of my escort. i just want it to be fast :mrgreen:
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PostPost by: 2cams70 » Sun Jan 22, 2017 11:16 pm

If it's a genuine Escort Twin Cam in good condition I personally wouldn't be racing it. If it's a standard 2 door Escort converted to Twin Cam specification go for it.

If the Cyprus authorities are talking "L" blocks they know what they are on about. If not why not use a non-L block 681F which will give more than 1600cc when bored to twin cam specs.
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PostPost by: Chrisis » Fri Jan 27, 2017 6:09 pm

It is pretty much a genuine twin cam converter to standard 1300 crossflow through the years for better economy :shock:

I'll be using it for historic racing so hopefully it will survive a lot more years 8)
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PostPost by: Chrisis » Fri Jan 27, 2017 6:19 pm

i'm building my engine using a 1600 crank in a 1500 701 L block together with 125E rods.

As i have high compression twink pistons if i machine the raised bump it will work or the low compression height piston is very different?
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PostPost by: 2cams70 » Sat Jan 28, 2017 2:08 am

I recommend doing yourself a favour and discussing your project with a good engine machinist first. The Lotus/1500 crank is 72.75mm stroke. The 1600 crank is 77.62mm stroke so with those combination of parts your pistons will be sticking out of the block by 5mm. Ford had two different types of 1600 crank too. 2737E casting number is the early type with small counterweights and there's a later type type which I think was introduced with the 711M which has larger counterweights. I'm not sure which is best for LTC application. The smaller counterweights would give more clearance between the piston skirts and the crank at BDC. I'm not sure why Ford changed the crank design but they were excellent engineers back then so I'm sure it was done for a very good reason.
1970 Ford Escort Twin Cam
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PostPost by: promotor » Sat Jan 28, 2017 6:46 am

2cams70 wrote:I recommend doing yourself a favour and discussing your project with a good engine machinist first. The Lotus/1500 crank is 72.75mm stroke. The 1600 crank is 77.62mm stroke so with those combination of parts your pistons will be sticking out of the block by 5mm.


That's not correct as you may have forgotten that stroke means you end up with half the difference (the stroke is the difference between the pistons at TDC and BDC, or the complete stroke) so the pistons will be sticking out of the top of the block at TDC by approx 2.435mm depending on other tolerances such as whether the block has been skimmed or not etc.

Conversely, the pistons will sit 2.435mm further towards the bottom of the bore at BDC. That equals the total stroke difference of 4.87mm.

If crossflow rods at 125.222mm were used over 125e rods at 122.5804mm that would give you an additional 2.6416mm of "poke" out of the top of the block - this would put you at around the 5mm you suggest (5.0766mm)


The 2737e crank is actually slightly heavier (I've weighed them) and considered by some tuners to be the stronger crank than the 711 one. The 2737e was the original crank as fitted to the transit van engine (2737e 6015) so perhaps a stronger one was thought necessary for a "load lugger". The 711m crank is still a perfectly suitable crank whatever it's history.

Chrisis wrote:i'm building my engine using a 1600 crank in a 1500 701 L block together with 125E rods.

As i have high compression twink pistons if i machine the raised bump it will work or the low compression height piston is very different?


You could machine approximately 2.435mm from the top of your pistons, but you will then likely need to machine the valve pockets deeper to compensate which will in all likeliness weaken the pistons possibly beyond safe use. Plenty of people have done it though but it's not something I would want to do for piece of mind.

Better to use a thicker head gasket and machine the pistons less to save their strength. Of course forged pistons would be better overall - custom ones even better.
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PostPost by: rgh0 » Sat Jan 28, 2017 7:01 am

There are suitable short compression height pistons available from various suppliers for this option. Machining the standard pistons down is risky and the valve pockets will end up to close to the top compression ring

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PostPost by: 2cams70 » Sat Jan 28, 2017 8:39 am

Crossflow in a Transit. That's interesting - must have been a real struggle with a bit of load ! Most of them had 3.3 or 4.1 litre 6cylinder Falcon engines here. A friend had a V4 "Dormobile" camper at one time but I think that was an import - definitely not a smooth engine ! For the engine's I've pulled down the 2737E crank was in MkII Cortina's and Capris. All MkII Escorts had the later crank (no 1600 Mexico Mk1's here).
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PostPost by: promotor » Sat Jan 28, 2017 8:52 am

2cams70 wrote:Crossflow in a Transit. That's interesting - must have been a real struggle with a bit of load !


I agree - don't think they lasted as a viable option for very long. As I understand it the crossflow engine was for a "around town" transit as opposed to the full-on band-equipment lugging van! The V4 engine was the normal engine for the majority of Transits here. Still not as good as a 4.1 litre though eh!

2737E cranks came in all crossflow blocks except for the 711m's as far as I know (which makes sense) but there's more than likely exceptions to the rule!
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PostPost by: el-saturn » Sat Jan 28, 2017 9:10 am

.....all the folks I know using a 711M block had one option: the 2737's or possibly a farndon for 3000?!! sandy
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PostPost by: Stevie-Heathie » Thu Feb 02, 2017 10:02 pm

I also have the 701M6015 block in my 1967 S3, (I suspect it is not original). I really am no expert by any stretch of the imagination but here is what it says on the Lotus Cortina website:

http://www.lotus-cortina.com/library/block/blocks.htm

701M 6015

Something rather special, reputedly of Ford Germany origin probably for the Escort T/C. Only made as an ?L? block, a meatier casting altogether, with big square main caps, the best basis for a competition engine, and much sought after. Many were used with 81mm bores towards the end of Ford?s engine exchange scheme for the 1500cc Cortina, so you know where to look!


Best
Steve
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PostPost by: Chrisis » Fri Feb 03, 2017 6:10 am

I had a conversation with burtons and they confirm that the Accralite forged piston for Zetec has the same piston pin size as the Lotus Twin cam and they do have a set of 83.5mm in stock.

They have an un-machined thick crown with a compression height of 37.2mm. They told me that the crown is thick enough not only for deep pockets but also to machine them so you are also left with quite a high intruder.

They also advise me to use the 4.930" Crossflow conrods with these and machine them(pistons) accordingly. This would give a better crank stroke to rod length ratio and allow to machine them with a higher intruder than if you used the Lotus length conrod.

does anybody actually did that?
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PostPost by: rgh0 » Fri Feb 03, 2017 10:02 am

Stevie-Heathie wrote:I also have the 701M6015 block in my 1967 S3, (I suspect it is not original). I really am no expert by any stretch of the imagination but here is what it says on the Lotus Cortina website:

http://www.lotus-cortina.com/library/block/blocks.htm

701M 6015

Something rather special, reputedly of Ford Germany origin probably for the Escort T/C. Only made as an ?L? block, a meatier casting altogether, with big square main caps, the best basis for a competition engine, and much sought after. Many were used with 81mm bores towards the end of Ford?s engine exchange scheme for the 1500cc Cortina, so you know where to look!


Best
Steve


it certainly is not original in a S3 but was used to build all twin cams from about 1970 on.
The above is true apart from the first sentence and first half of second sentence and a bit more later on :lol:

i.e. ignore this bit as its B****shit
"Something rather special, reputedly of Ford Germany origin probably for the Escort T/C. Only made as an ?L? block, a meatier casting altogether"
and
" the best basis for a competition engine"

Personally I prefer 120E blocks for my competition engines as they are better with the screw in pickup and also cheaper and more easily sourced !!

cheers
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PostPost by: Mazzini » Fri Feb 03, 2017 1:08 pm

Didn't this whole 701m thing kick off because of David Vizards book on tuning TwinCan Fords?

Any way I always thought the best blocks to have were graded LAA, didn't that mean that they had thicker walls?
Last edited by Mazzini on Fri Feb 03, 2017 4:03 pm, edited 1 time in total.
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