Lotus Elan and Lotus Elan Plus 2 Forums

While I've got the engine half-apart, I noticed these stampings on the front end of the block. Do they mean anything I'd find interesting (being the trivia-fan that I am), or are they just production-oriented markings that mean nothing to us enthusiasts?

LB is the block graded to wall thickness.

LC - thinner cylinder walls
LB - most common, average wall thickness
LA - Thicker walls and often selected for boring oversize
LAA - Holy grail, usually set aside at the factory for race motors.

These letter codes were assigned by a couple of crude bore wall thickness measurements through the core plug holes with calipers. After surveying a large number of blocks with Modern ultrasonic thickness measurements I find about 5% are the equivalent of LAA and capable of going to 85 mm bores safely. About 40% are equivalent of LA and can go to around 84 mm safely and about 50% are LB equivalent and you would not want to go over 83 to 83.5 mm bores the remaining 5% are LC equivalent where you would struggle to go beyond the Lotus 82.5 mm bore.

However to achieve this sort of percentage split you do need to offset bore the blocks to maximise use of the available wall thickness as it is rare to find the current bore centred in the bore casting. Without comprehensive ultrasonic checking and offset boring the percentage of blocks you can take out beyond 83 mm drops dramatically

cheers
Rohan

Interesting! I never knew that!
Is this a Ford thing, or do all manufacturers do this?

This was a Lotus specific thing to ensure the 1500 Ford blocks they used were suitable to go to their standard bore of 82.5 mm compared to the Ford standard bore of 81 mm without offset boring.

cheers
Rohan

I wonder what the A548 was about, especiaaly as stamped twice.

I wonder what the A548 was about? especially as stamped twice.

I have seen various other letter and numbers combinations on the front face. Not sure what they mean and if original or added later Often probably done by rebuild shops to match up to rebuild job numbers. I personally stamp all of my blocks with the number that matches my ultrasonic wall thickness survey records and engine build records so they have RHxx stamped on the front face.

cheers
Rohan

rgh0 wrote:These letter codes were assigned by a couple of crude bore wall thickness measurements through the core plug holes with calipers. After surveying a large number of blocks with Modern ultrasonic thickness measurements I find about 5% are the equivalent of LAA and capable of going to 85 mm bores safely.

Sonic testing is something that's been done in production for quite a while. I'm not sure what Ford UK used but here's a picture from Ford engine production in Australia in 1958.

https://www.pinterest.com.au/pin/451978 ... login=true

I suspect the Ford Kent block casting lines had their casting tolerances such that they did not need to do any thickness checks of the bore castings for their standard 81 mm bores. Lotus and / or Ford clearly needed to do something additional to ensure the blocks Lotus used for their standard 82.5 mm bores were suitable before spending time and money on the finish machining. I have read that custom calipers were used for this grading but never seen any details of what was measured and how. My own measurements confirm that it was practical to select blocks for the Lotus bore from the standard casting line tolerances.

Standard UK Ford blocks and "L" blocks have the same standard distribution of bore casting variation over the years from the early 116E and 120E nonLl blocks blocks to the last 701M L blocks and 711M blocks that I have measured. I have not measured up a sample of AX blocks from South Africa as very few of these have made it to Oz but these are supposed to have thicker walls but never seen any statistical modern measurement data to verify that claim. The new cast blocks now being done by Ford Motorsport in the USA have much lower variation in wall thickness based on the samples I have measured and you would struggle to go over 83.5 mm in any of them that I have measured. Someone is casting new blocks in the UK with thicker bore casting walls but the cost of these blocks is about double the USA ones.

cheers
Rohan

2cams70 wrote:Sonic testing is something that's been done in production for quite a while. I'm not sure what Ford UK used but here's a picture from Ford engine production in Australia in 1958.

Interesting discussion,



I'm not convinced that's ultrasonic testing. I worked in the Dagenham Engine plant in 1980 on assignment to Quality Control & that looks like air gauging to check & grade the machined bore size, note also the racks of pistons.

pharriso wrote:

2cams70 wrote:Sonic testing is something that's been done in production for quite a while. I'm not sure what Ford UK used but here's a picture from Ford engine production in Australia in 1958.

Interesting discussion,

536349_10151197376309293_212405714_n.jpg

I'm not convinced that's ultrasonic testing. I worked in the Dagenham Engine plant in 1980 on assignment to Quality Control & that looks like air gauging to check & grade the machined bore size, note also the racks of pistons.

I thought exactly the same, and have seen air gauges measuring bored holes to check tolerances in microns.

Would any of the production line cars with LAA blocks have been supplied over bored ?. Just curious as my +2 has a LAA block that i've not had apart.

steveh wrote:Would any of the production line cars with LAA blocks have been supplied over bored ?. Just curious as my +2 has a LAA block that i've not had apart.

Interesting, I always understood the extra A in LAA did indicate oversize bore.
But as so many aficionado on this site know all about these stamping I thought I'd better keep quiet.

My understanding was that LAA indicated a bore wall thickness at the top end of the range such that it was capable of being bored to 83.5 mm for 1600 cc class racing engines. With modern ultrasonic measurement and offset boring a high percentage of blocks are capable of this, but back in the day with limited wall thickness measurement by calipers and standard boring techniques with the bores location based on the block reference points rather than the actual bore casting outside diameter location much fewer blocks were judged capable of this, thus the reserving of LAA blocks for the racing program

If an LAA block ended up in a standard Elan originally I would have expected it to to be originally at the standard 82.5 mm bore at it got there just because the race program had all the blocks they needed. What bore its at now would depend on its rebuild history but by now I would have expected it to have had at least 1 re-bore if not more so it may be at 83.5 mm by now.

If the engine was not original to the car but installed later then a LAA block would likely have been in a race engine at some time and probably bored to 83.5 mm from new.

I guess if the race program had too many blocks finish bored to 83.5 mm and the road car factory was short of blocks for any reason then some race blocks bored to 83.5 with LAA marking could have ended up in a road car from new.

I am sure using 83.5 mm LAA blocks was one of the techniques that Lotus used to get such good performance out of its demonstrator cars

cheers
Rohan