Lotus Elan

701M L block question

PostPost by: Chrisis » Mon Jan 16, 2017 7:59 pm

Hey guys,

i found a 701M short block in a reasonable price.

After my mechanic checked it he found it to be a:

701M block with:
1) Large L letter
2) just under 82mm, I thought these late blocks came out as 83.5mm
3) crank is early type 4 bolt,
4) rods are not 125, they are normal 1500 116

Do you know the history behind this block?
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PostPost by: types26/36 » Mon Jan 16, 2017 8:29 pm

You have a mix of early and late parts, the 701 is the last of the short block 1500 engines and when made had a standard bore of 80.98mm (81mm) it was made for Lotus who bored it to 82.55 for use in the TC engines.

It found its way into some pre X flow Fords in Fords Exchange engine scheme in its 81mm standard bore size.

The 701's were never fitted with four bolt cranks or the skinny con rods in any original Ford or Lotus cars as standard, I would guess someone has rebuilt an early engine using a later block.
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PostPost by: Chrisis » Mon Jan 16, 2017 9:45 pm

thats a good point Brian

i'm just thinking if ford produce these blocks for mk2 lotus cortina and escort twin cam who would build it using 4 bolt crank and skinny conrods :|
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PostPost by: types26/36 » Mon Jan 16, 2017 10:03 pm

Chrisis wrote:if ford produce these blocks for mk2 lotus cortina and escort twin cam :|


I dont think the 701 was used in the MK2 Cortina Lotus but only in the late Twin Cam Escorts, the Elan Sprints, the later Plus Two Elans............ ...........and possibly in the S4 Elans?
As to who assembled it its anyone's guess :roll:
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PostPost by: el-saturn » Tue Jan 17, 2017 8:15 am

i'd say GOOD NEWS: all you need is the correct rods and crank plus some shells (PLUS whatever else may surface!) ............ have fun sandy
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PostPost by: rgh0 » Tue Jan 17, 2017 8:41 am

Ford used new 701m L blocks as replacement spares for 1500 engines when needed in the early 70's. So it looks like you block was used to rebuild an early 4 bolt 1500 block for a cortina or like with the standard Ford 1500 bottom end components. It was probably rebored to 82 mm at that time to suit the available pistons or some time during a later rebuild .

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PostPost by: Chrisis » Tue Jan 17, 2017 6:46 pm

thanks guys. whats your thoughts of the below engine spec?

As it needs re bore i was planning to bore it to 83.5mm, have 1600 crank fitted and find the right(shorter) con rods to send the pistons at the top of the block.

With cpl2 cams and some nice porting i'm hoping for a nice torquey engine.
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PostPost by: el-saturn » Tue Jan 17, 2017 7:40 pm

......have a look at the front of your block and to your left (upper corner) you'll probably have some pretty large letters punched/stamped on the surface which are LA, LB A N D if it says LAA (not many of them!) then you're safe otherwise you'll have to measure the availabe wall thickness (from the top with proper equipment) you shouldn't get under 1mm (0,7!!!!!!??????? anybody?) sandy PS rohan may have been that close! :mrgreen:
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PostPost by: vxah » Wed Jan 18, 2017 8:17 am

Chrisis wrote:thanks guys. whats your thoughts of the below engine spec?

As it needs re bore i was planning to bore it to 83.5mm, have 1600 crank fitted and find the right(shorter) con rods to send the pistons at the top of the block.

With cpl2 cams and some nice porting i'm hoping for a nice torquey engine.



Pretty sure with the 1600 crank as a minimum you want the standard length rods? Better if you can get shorter deck pistons and get the rods longer that stock?
All about stroke to rod length ratio and thrust loading with too shorter rod?
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PostPost by: elj221c » Wed Jan 18, 2017 10:21 am

If it me, I would go standard bore. It will then give you years of reboring. It's what I did with my 81mm 701 find.

Unless you are racing there is no need to go 83.5. A bit of a waste in my view.

Yes, CPl2s work nice with a 1700 twincam, I had one myself but on a decked 1600 block, but I expect you could do better with a modern cam profile.
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PostPost by: Chrisis » Wed Jan 18, 2017 11:11 pm

i understand that is a rare block, but hp is important driving my escort 8)

I was wondering if i'm using a 1600 crank can i fit the 1600 cross-flow sump or do i need the escort twin cam sump?
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PostPost by: rgh0 » Thu Jan 19, 2017 8:33 am

Any escort rear bowl sump will fit the block. You may need to do a little local grinding to get clearance of the rods depending on which rods you end up using with the 1600 crank.

The only thing rare about the block is the casting number. The block itself is identical in all important aspects to the earlier 1500 blocks produced by Ford and used by Lotus over the years of twin cam production.

The block should be good for an 83.5 mm bore but you should ultrasonically test it and offset the bores to the wall thickness even all around. The minimum wall thickness you want is 2.5 mm in local areas and ideally you want over 3 mm.

CPL2 cams are essentially the Lotus "D" or Sprint cam profile. The work well for a road car and have a good flat torque curve for a heavier car like an Escort. There are modern high lift short duration profiles that will give more torque and more power if combined with the right porting and other modifications but if building just a big capacity but otherwise standard engine they are a good selection.

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PostPost by: 2cams70 » Thu Jan 19, 2017 12:22 pm

If I had a rare L block like that I'd be machining and boring it the absolute bare minimum. Would not even deck it unless absolutely necessary. The increase in HP you will gain in going from a standard twin cam bore to +0.40" oversize (83.5mm) will be less than half a bee's dick and you are devaluing the block. Going on a diet and losing a few pounds for instance would likely result in a greater increase in vehicle performance!

Why not use a 711M 1600cc block instead if you are going down the large capacity route? Personally I prefer the standard combination of bore/stroke/conrod dimensions. The standard engine is very free spinning and smooth - why spoil it? The larger you go in capacity the rougher and gruffer it gets.

The best option as far as wet sumps are concerned is to use the Ford AVO big wing sump that was standard fitment on Mk1 Escort Twin Cams / RS1600's and 1600GT pushrod Mexicos. Rare and expensive these days however.

A sump out of a MkII 1600 Escort will physically fit and provide adequate crank clearance but you will get oil starvation on corners without attention to baffling. Do not use the sump out of an 1100 or 1300 Escort. It is shallower, has less oil capacity and the crank will hit. You will probably also need to drill the block to suit a rear dipstick location too - unless you are using a 711M block.
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PostPost by: types26/36 » Thu Jan 19, 2017 1:05 pm

2cams70 wrote: You will probably also need to drill the block to suit a rear dipstick location too - unless you are using a 711M block.


The 701 is already drilled for a dipstick, its just blanked off with a plug.
Dont forget if using the 6 bolt crank and rear bowled sump you will also need the "S" shaped oil pick up pipe, the rear oil seal carrier as well as the 6 bolt flywheel.
I would suggest you also get the Lotus cast front pulley and not the pressed tin piece of rubbish fitted on the early Fords ,the Lotus one is a slightly small diameter. There are also other steel ones available from places like Burtons and QED.
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PostPost by: Chrisis » Thu Jan 19, 2017 11:57 pm

thanks guys for all the help and advice.

i guess still young in age i cannot really value the rarity of this block as you have 8)

Beside of having already the pistons i just have in my mind that if another re-bore will be needed in the future i still have the option of sleeving it..
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