Lotus Elan

New block build

PostPost by: pptom » Sun Jul 28, 2019 11:02 am

Hello all, i've decided to re-block my tc and have aquired a NOS 1500 block. I'll be using most of the parts from my tc. The tc block was touch and go to repair without removing the std liners (on +40) and fitting new, so we honed and hoped for the best, but i fancy building something else and am not a stickler for originality although i will hang onto the
L block.
Obviously it will require a rebore to get to the standard lotus size, but i was wondering about crankshaft options. My current crank is -20 mains and big ends and 90k miles old, plus is worn at the rear main seal which i appreciate i could repair with a sleeve. I could transfer all of the bearings, so a cheap option.
Second option which i'm trying to explore is using a 711 crank. I understand its longer stroke so i'll need shorter pistons from somewhere, plus some grinding of the block for clearance, will it work with the 1500 block or do I have to go 1558?
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PostPost by: Gray » Sun Jul 28, 2019 11:16 am

My understanding is that the longer stroke 1600 crossflow crank can be used in the TC/1500 block with shorter conrods. Piston heights would need to be checked relative to the block height and possibly the block relieved for crankshaft clearance. The bottom of some pistons may also need to be relieved. Shorter conrods with a longer stroke crankshaft may not be the optimum configuration, but will give greater capacity without a taller block, I think I've got a spreadsheet somewhere with the options/capacities. I'm sure Rohan and/or others will be along shortly to provide more accurate advice.
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PostPost by: rgh0 » Sun Jul 28, 2019 1:02 pm

Almost all 1500 blocks will go to at least the 82.5 mm Lotus bore in my experience. Most will go further to 83.5 mm and some to 85mm. People who go beyond 85.0 mm either have a unicorn block or are kidding themselves. There was nothing special about L blocks of any flavour as the same proportion go to 83.5 or 85 as a standard 1500 120E block in my experience.

I would get the walls checked and then offset bored to maximise an even wall thickness for what ever bore you want to run. Pistons most easily available at standard 82.5 mm and then increments of +20 thou to 83.0 mm or 83.5mm. Beyond that your typically into the custom forged piston range which is not that expensive these days.

You crank should be reusable if the journals are in good condition and all it needs is a sleeve on the rear seal.
A 1600cc / tall block long stroke crank can be used in a 1500 / short block. You need to check clearance and some minor grinding may be needed. Dave Bean and others can supply the low compression height pistons needed. Makes a nice road engine with a 83.5 mm bore and the right cams,exhaust and carb setup plus a little porting and big valves especially for a Plus 2 :D Now you have me down a totally different path :lol:

cheers
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PostPost by: pptom » Sun Jul 28, 2019 1:51 pm

Thanks Rohan. This is on my +2 with a recently ported head and qed360 cams. I guess the sensible option is just to bore 1558 and swap everything over, the only expense being pistons, gaskets and rebore. I suppose longer term, I could keep a lookout and save up for a more ambitious build.
I'm guessing the stroker bean pistons would be a fair cost imported into the uk. Plus i'd need to find a good crossflow crank, then grind, new shells etc at the minimum -This engine build lark is a rabbit hole!
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PostPost by: rgh0 » Sun Jul 28, 2019 2:02 pm

pptom wrote:Thanks Rohan. This is on my +2 with a recently ported head and qed360 cams. I guess the sensible option is just to bore 1558 and swap everything over, the only expense being pistons, gaskets and rebore. I suppose longer term, I could keep a lookout and save up for a more ambitious build.
I'm guessing the stroker bean pistons would be a fair cost imported into the uk. Plus i'd need to find a good crossflow crank, then grind, new shells etc at the minimum -This engine build lark is a rabbit hole!


When building engines I sometimes think there is no "sensible option".

I doubt the low compression height pistons will be much more than standard new pistons but I don't know the relative prices in the UK. Journal shells are relatively cheap and I routinely replace them with any rebuild. The only real additional cost is the 1600 crank. That is unless you go for QED 420 cams and spring pack that the bigger displacement engine in a Plus 2 will really love ... sorry down that rabbit hole again :roll:

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PostPost by: 2cams70 » Sun Jul 28, 2019 3:07 pm

Interesting thing to consider when mixing and matching conrods, pistons and crankshafts:

https://engineering.stackexchange.com/q ... crankshaft

It's something I've wondered about why 1500 pushrod and Lotus Twin Cam engine have different crankshaft counterweights and why early 1600 crossflows with small chamber in head and later 1600's with flat heads have crankshafts with different counterweights.

It's something engine builder's rarely consider but the OEM's do. If you don't have the counterweight weight right relative to the weight of pistons and conrods the crankshaft will be subject to internal bending moments (and hence greater stresses) and the crankshaft bearing life reduced.
1970 Ford Escort Twin Cam
1972 Ford Escort GT1600 Twin Cam
1980 Ford Escort 2.0 Ghia
Peugeot 505 GTI Wagons (5spdx1) (Autox1)
2015 Honda City 5spd.
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PostPost by: elanman999 » Sun Jul 28, 2019 3:18 pm

When I built my 1700cc Elan engine I used an L block with 711 crank and 1500 rods with some 83.5 pistons from Burtons. The pistons had the correct crown height but had very thick tops so I lightened them by machining out the under side of the crown. The top of the crown will also need machining to get valve pockets and may need a small bowl made for a useable CR.

If I did it again I would look into getting some pistons from the USA. If DB makes some to fit then that would be the easy route. Or I would get some made from JE pistons, for JE you will need to go via a UK company and I have used Cambridge Motorsport in the past. I had some made for another engine and the cost was not much more than forged pistons made in the UK and the delivery was half the time for bespoke made ones.

I'll look out the Burton piston part no for you if you want go that route.
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PostPost by: pptom » Sun Jul 28, 2019 3:30 pm

Thanks all, interesting about the counterweight issue and something i'd not considered.
Think i'll take the easy way out and build a standard bottom end....
For now.
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