Lotus Elan

Engine / Camshaft identification

PostPost by: JonB » Thu Aug 29, 2019 8:55 pm

Hi

The service manual gives cam to follower clearances and for all engines the inlets are 5-7 thou but for the exhaust side there is a difference between engines. 6-8 thou for engines before 9952 and 9-11 for engines 9952 and later.

Problem is I'm not sure what that number relates to:-

  • The body plate says the engine is P1288 07
  • The block has the ID 701M6015BA cast into it
  • Some other marks on the block: 2J28, B-A, L

Which one correlates to the clearance engine cutover number? I'd assume 6815 but need to be sure. I measured my clearances and found all inlet valves at 5 thou and exhaust valves at 9 (cyl 1), 11 (cyl 2), 8 (cyl 3) and 11 (cyl 4).

Also, about my cams. they have two grooves on their sprocket mounts and markings as follows:

  • Exhaust cam: B26E351 and C
  • Inlet cam: B26E351, 13.9, A and MC23929

What does this tell you? Standard Big Valve cams or something special?

[Edit: According to this thread viewtopic.php?f=39&t=16829 they are definitely Sprint cams as the double groove is the deciding factor. But A and C seems odd.]

Finally, the head. It has GX71 stamped at the rear above the clutch cover, upside down and N stamped into a raised disk in front of cyl. 1's spark plug. Does it mean anything?

[Edit: The head ID numbers are cast in a hard to see location. I'll get out a dentist's mirror and try to read them off..]

Thanks.. back to the dashboard now..
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PostPost by: draenog » Thu Aug 29, 2019 10:29 pm

The block numbers you show are not the engine number - this should be on the flat section above the engine mount on the carb side. As your car is a +2S 130, the number should have a P prefix (Big Valve Weber, domestic). So the number on the ID has the right prefix, but it shouldn't have a space, and is far too large (I would imagine it would be in the 20-30 thousand range?).

The N on the head marks it as Big Valve.

As far as the clearances, it will be the later values, as all Big Valve engines are after 9952 (my car is a +2S, earlier than yours, with a non-Big Valve engine and its engine number is F21598)...
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PostPost by: JonB » Fri Aug 30, 2019 8:22 am

I found the engine number stamped on the block where you said. It's P28807, so I think the number on the plate should be interpreted as P/28807 (slash, not "1"). However, 28807 is a long way from the cutover number 9952 that is shown in the service manual. I cannot imagine they made 18,885 engines after the cutover.

I also located the head markings on the exhaust side, which are WM9403 (at the front) and A 26E-311 (under the thermostat housing).
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PostPost by: nmauduit » Fri Aug 30, 2019 8:48 am

JonB wrote:[*]The block has the ID 701M6015BA cast into it
...
I'd assume 6815 but need to be sure. seems odd.]


your cast number seems to indicate a [edit : 701 / somehow the number went out] block - there are a number of discussions and papers on engine numbers, including

https://www.lotus-cortina.com/library/block/blocks.htm

the engine number is stamped (not cast), see for instance

http://www.lotuselan.net/forums/viewtopic.php?f=39&t=28613&start=

as for valve clearance, the head is what matters, since it may have been swapped since the unit left the factory. Also, actual clearance may be selected considering other factors (different cam profile, spring, use etc.) e.g. I have installed Q420 cams on my street big valve, I installed them with clearances on the high side (8/10 thou).

ps: I find making note of measured clearances useful for maintenance and keeping track of engine condition evolution.
Last edited by nmauduit on Fri Aug 30, 2019 9:42 am, edited 1 time in total.
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PostPost by: types26/36 » Fri Aug 30, 2019 9:25 am

JonB wrote:Hi
The body plate says the engine is P1288 07
The block has the ID 701M6015BA cast into it
Some other marks on the block: 2J28,
.


The 701M block is correct for a 72 car.
The 2 J 28 is the date code of the block.
(2) is the decade.....1972
(J) is the month ......September
(28) is the day.........28th
Thus your engine is correct for a 72 Plus Two, the engine having been manufactured on 28th September 1972.
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PostPost by: rgh0 » Fri Aug 30, 2019 9:49 am

The exhaust valve clearance was changed due to a change in Exhaust valve material or a change in the take up ramps in the cams or perhaps just because Lotus decided the clearance was to small. i would not worry about it today with any twin cam. If rebuilding any engine today I would use the later clearances.

Your engine block is a big valve of around 1972 vintage which is what would be expected for your car based on all the numbers as others have pointed out.

The GX71 code on the head i have never been able to fully decode but I believe the first letter is a year date code with G being 1972. The second letter I believe is a batch code and the numbers are numbers within that batch. This coding replaced stamping the engine number on the head around 1967 starting with B.

i.e. My best guess is as follows but given Lotus record keeping and how heads have been swapped over the years its hard to be definite
B 67
C 68
D 69
E 70
F 71
G 72
H 73


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PostPost by: JonB » Fri Aug 30, 2019 10:43 am

OK, so I think we've established that the engine block and head are original to the body, which is great, and confirms my view that the car is very original. Thanks to all for the information!

Looking at the clearances, it seems that only cyl 3's exhaust valve might be a little tight at 8 thou, but the rest are in range. Maybe 2 and 4 exhaust valves are a little loose at the higher end of the range. Seems to me I should leave alone for now (after all, the clearances can be done any time without removing the head).

I'd like to ask about the cams. Yes, they have dual grooves indicating Sprint spec (as expected for a BV head) but I have a C cam (ex) and an A cam (inlet). Is that normal, or am I just concerned about nothing?
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PostPost by: rgh0 » Fri Aug 30, 2019 11:03 am

Never been able to clarify all the various cam numbers apart from the Lotus part number on the cams. The two grooves probably / definitely signify a type D big valve cam, nothing is absolutely certain . Easy enough to check if really a big valve specification by measuring duration, base circle and lift but given the orthogonality of the rest of the engine I would suspect the cams to be original also

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