Lotus Elan

701M L block question

PostPost by: rgh0 » Fri Jan 20, 2017 12:05 pm

Why does everyone consider a 701m L block is desirable ?

start "rant"

The numbers on the block may be rare but the rest is the same as a 120E block out of any old 1500 cortina from the 60's and the oil pick up arrangement on a 120E block is better !

Will someone please tell me why they think a 701M L block is better ??

I would not waste ( and do not waste) my money on 701m L blocks. Chris needs to buy one due to his stupid Cyprus registration rules that says his escort has to have a 701m block to go with a twin cam head even if the particular head is not original to an escort and originally came on an earlier block. But if you dont have that problem don't waste your money.

end "rant"

cheers
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PostPost by: promotor » Fri Jan 20, 2017 12:21 pm

People want the period-specific block for their car regardless of its inherent engineering features. All 701m blocks should have square caps though so that is a plus point.

As these blocks were found in later Escort Twincams it's important to have one in a late car if you want it to be period correct. Escort Twincam = rare car and commands high price. 701m not as easily found as other blocks and therefore commands prices.

Makes sense to me from a numbers point of view but no 701m block comes close to the quality of the early Lotus 120e type block I have with mega thick bore walls. I'll quite happily sell both of my 701m blocks for high prices if that's what people want.
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PostPost by: el-saturn » Fri Jan 20, 2017 12:24 pm

my 701 was part of the package AND i changed the cam cover to the correct type (1965 s3) cheers: no elan weather forecast!! sandy
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PostPost by: rgh0 » Fri Jan 20, 2017 12:30 pm

Hi Promotor
I think your agreeing with me !

701m L blocks are "rare" and "valuable" for the matching numbers people ( like the Cyprus registration officials) not due to any inherent other benefit.

I build my race engines from my stock of blocks which have the bore wall thickness measured to make them "rare" and "valuable" 120E blocks :lol:

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PostPost by: promotor » Fri Jan 20, 2017 12:46 pm

rgh0 wrote:Hi Promotor
I think your agreeing with me !

701m L blocks are "rare" and "valuable" for the matching numbers people ( like the Cyprus registration officials) not due to any inherent other benefit.

I build my race engines from my stock of blocks which have the bore wall thickness measured to make them "rare" and "valuable" 120E blocks :lol:

cheers
Rohan


I agree with you when I have my engine builder head on but I don't always wear it!

Their loss is others gain really! That's why I'm doing my 1700 twincam in a 120e block - just as good as most others out there!

As to the OP's point abut bore size - what size pistons are you fitting and are they new or 2nd hand?
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PostPost by: rgh0 » Fri Jan 20, 2017 1:00 pm

I normally build 1600 cc race engines with 83.5 mm bores and standard 1500 stroke cranks. Most blocks will take a 83.5 mm bore with a minimum of 2.5 mm wall thickness or more if you centre the bore in the casting with offset boring. Its just the blocks that have been bored over 82.5mm without centering the bores that are impossible to recover as they have used all the bore wall thickness on one side already. A nice 81.5 or 82 or 82.5 mm 120 E block is best :D

I normally line bore and fit new steel caps so the original round caps are not a problem
I use new JE 83.5 mm forged pistons when building my race motors

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PostPost by: 2cams70 » Fri Jan 20, 2017 3:19 pm

All Escort Twin Cams to be period correct should have an "L" block. Either 681F (round mains) or 701M (square mains). Only the 681F and 701M blocks have the boss at the rear to accommodate a rear dipstick location. The 120E and 2731E 1500 blocks don't have this boss.

My theory on the "L" is that it's sole purpose was to provide an easy visual identification for the assembly line workers to distinguish between 1500/Lotus blocks and the 1600 crossflow block. The 1300 crossflow block is easy to distinguish because the deck height is almost level with the water pump mounting holes. The 1500 and 1600 blocks aren't so easy to visually distinguish because both decks sit considerably above the water pump mounting holes - the 1600 just a little bit higher than the 1500. I know there are 681F 1600 crossflow blocks, not sure about 701M 1600 crossflow.

The cast "L" came into being around 67/68 at the same time as the introduction of the 1300 and 1600 crossflow motors. Prior to the crossflow there was just the 1200 block (easily distinguished from the 1500 pushrod / Lotus block) hence no need for an "L" for visual identification of the 1500.
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PostPost by: rgh0 » Fri Jan 20, 2017 9:38 pm

I normally build 1600 cc race engines with 83.5 mm bores and standard 1500 stroke cranks. Most blocks will take a 83.5 mm bore with a minimum of 2.5 mm wall thickness if you centre the bore in the casting with offset boring. Its just the blocks that have been bored over 82.5mm without centring the bores that are impssible to recover. as they have used all the bore thickness
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PostPost by: Chrisis » Fri Jan 20, 2017 9:55 pm

As Rohan mentioned i purchase a lotus twin cam head to use it with the 711M 1600 crossflow block, but then i found that in Cyprus in order to register a lotus twin cam head into mk1 escort it needs to come with 701M block.

My personal opinion is that the 701M is rare if used in an escort twin cam. For the rest is just waste of money.

After all the money spend building a nice twin cam i wish at the end of the day it will worth it compare to my 1600 cross-flow.
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PostPost by: 2cams70 » Sat Jan 21, 2017 12:00 am

If that's the case the Cyprus authorities have definitely got it wrong! For an Escort Twin Cam to be correct you should be looking for an "L". The casting number is not that important. You can bring a 681F block up to 701M standards by fitting square main caps.

If I were you and big capacity was the sole purpose of your engine build I'd be looking for a non "L" 701M 1600 crossflow block. By the Cyprus authority rules that would still be OK. I think they probably do exist - perhaps someone on here or one of the Ford forums could confirm?
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PostPost by: rgh0 » Sat Jan 21, 2017 1:41 am

The 701M L block was the 1500 height equivalent of the 711M non L block that was 1600 height. i don't believe there was a 701M non L block as Ford was only making these blocks for Lotus.

The L appears on earlier castings i.e.e 681F 2737 and 120 E but its appearance is far from consistent in blocks used by Lotus for the twin cam

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PostPost by: 2cams70 » Sat Jan 21, 2017 4:19 am

The riddle of the Ford block numbers will probably never be solved!!

I know for certain that there were "L" and "non L" 681F blocks. The "non L" were at 1600 block height. Did any of you guys see the Twin Cam engine advertised on Ebay a couple of weeks ago in Queensland with the red coloured block? Unfortunately I did not save the ad. It had a 681F block non-L and required a spacer for the timing chest because it was at 1600 block height.

Out of interest does anyone know what diameter the tappet bores are in a 701M block (small or large)? With the pushrod motors everything is small up until the 711M block which went to large diameter. The square main caps were introduced for the 691M but this still had small diameter tappets.

There does not appear to be any relationship between the first 4 digits of the engine code and the deck height. 711M's for instance are available in both 1300 and 1600 deck height.
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PostPost by: Craven » Sat Jan 21, 2017 11:42 am

Hi,
I thought the 1600 height block in the series was a 691F. !
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PostPost by: Chancer » Sat Jan 21, 2017 3:55 pm

I have a 1600 681f block engine dry stored back in the UK, it was my first engine in my Westfield, it came out of a 1967 Cortina T, originally it was Xflow with downdraft weber with the semi-chambered head and smaller bowl pistons, non square main bearings and the smaller tappet diameter.
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PostPost by: Chancer » Sat Jan 21, 2017 4:05 pm

Re the square main bearing caps being stronger which they undoubtedly are, were the non square ones actually too weak or was it just perhaps a production change to reduce cost?

I ask because having tuned several 681F blocks to a reasonable degree I had never experienced problems nor seen others, no doubt for the all steel screamer race engines of the day it was good insurance but was it needed or has it just passed into folklore?

I did break a tappet on a couple of occasions and they was the larger diameter but it was caused by the engine kicking back and running backwards on start up, the combustion explosion was resisted by a dinner plate inlet valve trying to open against it, the weakest link was the tappet not the rocker arm.

I Wonder how many of the period tuning "strenthening" bits were actually needed other than in a theoretical sense but they made the suppliers lots of money and who was going to gamble without them? -Not me back in those days, I had yet to become a Chancer who needs to put recieved wisdom to the test.
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