L Blocks Revisited

December 29 2005


An emailed correspondence received this past summer from John Wood called into question the suitability of "scrap-yard found" L Blocks (with 1500cc bore size) for re-sizing to 1558cc bore size. Previously, I had thought they would be ideal, as the previous article also suggests. It has taken me many weeks to put this all together, and for that I apologize. This summer, John wrote:

"In your discussion on finding L blocks in standard cars I think you have missed the reason for this. L blocks which failed the quality standards for lotus were cascaded to the standard cars. Therefore you must not assume that such blocks will bore to lotus oversizes. The lotus bore size was chosen to allow + .040" oversize to get to the 1600 cc class limit. Reject blocks will not allow that as they are likely to become porous." J. Wood, 8/30/2005.

To which I replied...

"But I wonder... I can understand that Lotus would reject some blocks, and that those perhaps would then revert to Ford production. But... what technology would have been available to a small company like Lotus, 40+ years ago, that would allow them to measure and gauge _potential_ porousity if bored beyond a "standard" over-bore? Remember, the L blocks would have to have been rejected before they were even bored to 1558cc capacity, as they were then assembled as 1500cc engines. Could it actually have been possible for Lotus to reject blocks for this reason?"

To which J. Wood replied...

"More on the subject of blocks:
What you must appreciate is that all the blocks were cast at the same iron foundary. The only differerence in the process was the use of different patterns for making the moulds for the L blocks. The initial quality inspection would have been done before the blocks went onto the machining line. Clearly there would have been sufficient technology for such quality checks to be robust enough to identify poor castings for both the normal and L blocks.

I've never been able to track down anyone who worked in the foundary or Ford engine plant but I did see the same process at Leyland where I worked. Based on that experience I think it is likely that all the blocks would have gone down the same machining line since 95% of all the machining is the same for all blocks.

At the end of the line, the L blocks would then have been separated and taken for further specialist machining (i.e. bigger bore and other clearances). There was undobtedly a detailed quality inspection late on in the machining process because the Lotus blocks were "graded" according to cylinder wall thickness. The grade is stamped at the top left hand corner of the front face using letters "A" and "B" in various combinations - A, AA, AB, etc. (I'll need to check up from my records exactly what they were). This was essentially an indication of cylinder wall thickness.

Blocks destined for works competition engines were specially selected for maximum wall thickness early in the production process. Identified blocks were "escourted" and taken on and off the line at various points for specialist attention. Off-line machining was done to maximise metal thickness at critical stress points. Of course all that was highly secret at the time. Ex-works components are thus highly desirable but very difficult to identify. I've had my hands on a few and they really are remarkable.

Checking wall thickness is not that difficult. It can be done through the core plug holes and water pump cavity and down the water jacket holes on the top of the block. You just need some 'trick' calipers." J. Wood, 8/31/2005

To which I replied...

"Yes, that's what I mean. Take cylinder wall thickness. (And mind, I am NOT speaking from any perspective of possessed knowledge- only thinking it through) If you were to measure the cylinder wall thickness using fiddly-bits-trick calipers through water jackets, using an un-machined inside cylinder wall as one of the bases, then you could only have a VERY rough idea as to wall thickness- you might be measuring from a high-point of cast material, you might be measuring from a low-point of cast material. I don't think you could know with any kind of certainty what might be left behind after machining. Whereas if you machined the bore, THEN measured the cylinder wall thickness, You would have a much better idea as to what would be "left behind" the machined surface through to the water jacket, which WOULD be useful in grading wall thickness.

Which means...

If Ford machined the L blocks to 1500cc capacity, _then_ (and only then) they might have been able to grade them as "thick enough" for Lotus, and then sent them off to Lotus for further machining there, including boring to 1558cc capacity. Or if they did not meet the "thick enough" standard, then they might have been diverted to their own destiny as Ford line 1500cc pushrod engines.

The only other option, which I _used_ to believe was the practice, would have been to ship un-machined (or at least, un-bored) L blocks to Lotus.

I have been writing to a former Lotus employee, and will ask him if he has any recollection as to the state-of-finish of the L blocks. If they were bored to 1500 size by Ford, and then shipped, then what you say makes perfect sense. On the other hand, if they were un-bored on delivery, then its possible that the diverted "L block 1500 pushrod engines" could be fine for 1558cc use. The blocks would have been diverted to the Ford line earlier in the process, possibly simply because of over-production at any given time, not because of original thin-ness. Its a good question to try to resolve, I think."


And I have now heard from J. Pierson, an acquaintance and former Lotus employee, who mailed to me a copy of a letter he received from M. Warner, another former employee of Lotus.

It seems that initially, L blocks were delivered to Villiers already bored to 1500cc capacity, but that current with the introduction of the Lotus Cortina, Ford then delivered the L blocks with un-machined bores, BUT... M. Warner presumes that only blocks that "...failed the "Lotus test" were automatically passed through for 1500cc machining." Read the letter! M. Warner also believes that scrapyard-found L Blocks would need to be sleeved before machining.