Cosworth "L" Blocks

[avro]

Its been more years than I care to remember when a good friend Bryan Moorcroft visited my workshop and rummaged through a pile of Lotus blocks and engines whilst engaged in research for his article on Ford and Lotus Cylinder blocks. The article originally titled What the "L" was written for the Lotus Cortina Register Magazine but can be found on several sites including this one. Over the last 25 years or so since the article was published some odd blocks have emerged with unusual casting numbers. Some were less common blocks that Bryan was not aware of at the time and some others with identification numbers completely different to that generally accepted as being correct for a particular period of manufacture.
A few years ago I purchased a batch of Lotus engine components and amongst the blocks was a 701M Lotus block with COSWORTH cast into the side. It was on standard Ford Pushrod bore size of 80.98 and unlinered. The witness marks and remnants of gasket material on the front face showed clearly that the block had been used with a timing cover for either a Ford pushrod engine or perhaps a BDA. I spoke to several historic engine builders but none were aware that these blocks existed. I thought a call to Cosworth would shed some light on its origins and it turned out that a batch of blocks were cast in the early seventies for development work on small capacity BDA engines. Thinking that this was quite a rare item I was suprised when another of these turned up a few weeks ago that had been fitted in a Mk 1 Cortina. It would seem that some of these also managed to find their way into the Ford engine reconditioning scheme as reject blocks.



Nick Stagg

[EnfoKen]

Thanks, that's great information. I was at Cosworth for 10 years and would rummage through the archives every time I was in Northampton and never cam across anything on those.

KA

[512BB]

And I take it Nick, that as your topic title suggests, round the other side of the block, there is an L cast between the engine mount?

Also, are there any markings on the front face re grading ie AB, AA? But more interestingly, what differences do you detect between a standard 701M and the Cosworth 701M block?

I shall have to have a look in my stores, see if I have any hidden gems.

Leslie

[avro]

Hi Leslie

Yes the block does have the L cast into the side but has no grading letters stamped into the front face.
Even taking into account that the block is on standard Ford bore size of approx 81mm when I compare it to an average 701M block I've calculated it to be about 8 lb heavier. Its clear to see that the cylinder walls are much thicker. The round and triangular waterway holes on the top face are much smaller and the block walls within the waterjacket drop vertically down from these smaller holes. The round holes situated between and to the side of each pair of cylinders on the top face measure between 3mm and 4mm compared to 7mm on another 701M block I have.
Measuring from the edge of these holes to the cylinder bore shows the wall thickness to be 10.5 -12mm at these points. However measuring the wall thickness through the rear core plug and waterpump aperture shows it to be a good deal less. Perhaps this is the reason why this block was rejected and found its way into a Mk1 Cortina via Fords engine exchange scheme.

Regards

Nick

[rgh0]

Hi Nick
I would love to see the results of an ultrasonic survey of the bore walls. If they are consistently 10 plus mm on a standard bore then the bores would have to be siamesed together. The biggest consistent bore casting OD I have measured on a ford block is around 92 mm ( and that was on a standard 120E block) which is about as big as you can do with sand casting technology without siamesing the bores.

Like to see some more photos especially around the bearing support areas as these are other details I would have expected Cosworth and Ford to have played with in a special BDA development version.

cheers
Rohan

[avro]

Hi Rohan

On further inspection I can see no difference in the casting in the area of the main bearing housings compared to that of another 701M block.
On measuring the casting through the core plug apertures the gap between the bores is a little under 3mm giving a wall thickness to the cylinders at this point of about 6mm. If I measure the block through the rear core plug hole and waterpump aperture then the wall thickness at these points is also much the same at about 6mm.

Interesting re your findings on earlier 120E blocks , I recently had one that was fitted with a set of the very old Hepolite Powermax forged 85mm pistons on a 30thou oversize . It had however just broken through the oil gallery drilling between number 2 and 3 cylinders and a thin wall sleeve had been fitted into the gallery as a repair. Going by the bore wear the engine must have run quite successfully for a number of years.

Cheers
Nick

[rgh0]

Thanks for the information Nick

It sounds like they pushed the sand casting to the absolute limit to get a 93mm bore casting OD with 81mm / bore and 6mm walls and just 3 mm between them from the 96mm bore spacing. This is something you could do with a special run development casting but not something they would try for mass production. The 3mm thick sand mould between the bores would have been just to fragile and to many failed castings would have resulted when it collapsed during the pouring to be practical for mass production.

From my measurements Fords target bore OD was around 90.75mm with the normal variation being between 90mm and 91.5mm with a few outliers down to 89.5mm and few up to 92mm.

That Cosworth un-bored block with 93 mm casting OD would make a great base for a big bore engine with offset boring to centre the bore in the castings

cheers
Rohan

[promotor]

Nick.

I've been trying to find the details of a Cosworth Lotus blocked engine that a friend had but have been struggling.
I seem to remember however that it was on a 85.6mm bore and I remember him calling it a screamer so I believe it was a short stroke crossflow.
I'm not sure if he also had a BDA with a Cosworth block. The exotic engines he has had is almost unbelievable and he thinks nothing of spending big on engines. Maybe I will only have to wait a short while for him to buy another Cosworth one!

I will keep looking to find the info and will post it if I find it.