Lotus Elan

Short block long stroke engine

PostPost by: 2cams70 » Sat Jan 27, 2024 1:16 am

One thing not to gamble with is the jackshaft and the oil slots. They regulate oil flow to the head. Get it wrong and you'll really get it wrong. Used LTC jackshafts aren't particularly expensive. I'm sure when they were developing the LTC prototype engines had the standard pushrod camshaft fitted with one slot. Obviously Mike Costin, Duckworth, et. al. worked out that one, two or three slots wasn't enough. Feel free to argue with those guys that they got it wrong.

I know aftermarket replacement jackshafts have full circle oil slots. Full circle oil slot jackshafts were standard on the BDA engines however BDA engines had an oil regulating orifice fitted to the block which the LTC engine doesn't have as standard. From what I hear people have fitted these jackshafts to LTCs seemingly without issue but personally I'd just go with as per original.

Couple of pointers:

1. ARP bolts are better than ARP studs for head fastenings on road engines
2. There's a gasket manufacturer here in Australia that can make up any size of composite gasket you want for a LTC. In fact when I first rang up my local agent for Cometic they said speak to this guy - that's how I found out about them! Rohan I know you posted a while ago about having purchased one of these gaskets. Have you had a chance to use it under duress in race application yet?
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PostPost by: nmauduit » Sat Jan 27, 2024 10:41 am

2cams70 wrote:Couple of pointers:
1. ARP bolts are better than ARP studs for head fastenings on road engines


I don't understand that... bolts may be more convenient to some people or possibly cheaper, but torquing them is not as accurate as just torquing the nut upon studs so underclamping pressure may happen. Then I fail to see why a road use of an engine would warrant a specific type of head fastener rather than a more reliable one suited for race (except an unjustified price difference possibly).
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PostPost by: 2cams70 » Sat Jan 27, 2024 12:27 pm

nmauduit wrote:I don't understand that... bolts may be more convenient to some people or possibly cheaper, but torquing them is not as accurate as just torquing the nut upon studs so underclamping pressure may happen. Then I fail to see why a road use of an engine would warrant a specific type of head fastener rather than a more reliable one suited for race (except an unjustified price difference possibly).


Particularly when you have an Aluminium head bolted to an iron block it's best that you have some flexibility between the two because when heated Aluminium expands around 3 times as much as iron. The ARP studs are whopping great thick tree stumps that are less flexible than the thinner ARP bolts and the OEM bolts. If you don't have enough flexibilty between the head and block the gasket has to compress and uncompress rather than the fastener compensating for thermal expansion by acting like a spring.

Not good for the gasket. Road engines used often typically go through more thermal cycles than race engines used occasionally and dismantled often so the effect is amplified. You don't really need higher than standard clamping loads between the head and block unless you are significantly increasing the pressure inside the cylinder such as when forced induction is being used.
1970 Ford Escort Twin Cam
1972 Ford Escort GT1600 Twin Cam
1980 Ford Escort 2.0 Ghia
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PostPost by: rgh0 » Sat Jan 27, 2024 6:32 pm

Given all the tolerances that can affect the centering of the gasket bore on hte piston bore I always use 85 mm head gaskets on 83,5 mm piston bores. Cometic make a 85 mm CFM one but you typically need to order it specifically.

The Australian ones are made by a company called Gasket Solutions. They will custom make both thickness and fire ring bore to suit your needs. i have an 85mm bore one but have not used yet. A firend of mine has used these for a while on his race engines with zero problems.

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PostPost by: ill_will » Fri Feb 02, 2024 7:41 pm

Burton Power have Cometic 85mm CFM gaskets in stock at the moment, 0.043" thick, so I now have one which will hopefully fit. Delivered next day, taped to a sheet of ply, which is nice.

It appears to be made (or at least the gasket material) by Victor Reinz - I don't know if Cometic stamp them from blank sheets of gasket material or farm them out wholesale.

I decided to add a groove to the jackshaft, per the QED aftermarket ones. It will be a voyage of discovery. The head differs from the standard design in other ways too as it doesn't have cam bearings or tappet sleeves. Assuming the oilway seals at the gasket, the clearances in the head are at lower end of spec and should meter the flow. Time will tell.
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PostPost by: rgh0 » Sat Feb 03, 2024 4:17 pm

Ivhave used the jack shafts with the continuous for some time now without problems, but Ido tend to ensure my cams bearing clearances are in spec also. I think comments about excess oil in the head and the need for a retrictor come from worn cam bearings being used.

Check the Cometic 85mm CFM gasket as the one I have is missing a couple of the water jacket holes at the rear of the head. You should add these if missing

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PostPost by: ill_will » Sun Feb 04, 2024 9:07 am

Good to know about the jackshaft, thanks Rohan.

I did a quick comparison and spotted that several of the waterway holes in the central area and which on the original are very small, are the same size as the others. They all appear to be present though. It will need modification as the oil drain tube cutout is not present. I'll post a photo when I have both side by side.
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PostPost by: 2cams70 » Sun Feb 04, 2024 10:15 am

It seems that Cometic don’t actually know what a Lotus Twin Cam engine is - I don’t imagine it’s a commonly known about engine in the USA. They have probably assumed the gasket to be the same as that for a pre-crossflow pushrod engine or a BDA and it isn’t. If it’s the wrong gasket it’s better that Cometic be told it’s the wrong gasket than you attempting to modify the one you have.
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PostPost by: ill_will » Mon Feb 05, 2024 8:37 pm

Old vs new gaskets, for reference. The fire rings measure approx 85.5 mm, vs nominal 85 mm.

IMG_20240204_103827 (2).jpg and
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PostPost by: ill_will » Sat Feb 10, 2024 10:05 am

James put a video up of him balancing the crank assembly, starts around 8:40

https://youtu.be/O9aCC9liW-8?feature=shared
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PostPost by: ill_will » Sat Feb 10, 2024 10:59 am

Block painted and nearly ready to start assembly.

IMG_20240205_190537.jpg and
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PostPost by: ill_will » Sat Feb 10, 2024 11:01 am

Does anyone have any advice on what to use to oil the bores if the engine might sit for a while before being run, but that doesn't affect bedding in the new rings when it is run-in? I've used ATF for the moment, but not sure if that's a good choice.
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PostPost by: ill_will » Sat Feb 10, 2024 11:07 am

Jackshaft, oilway bungs and shells installed:

IMG_20240209_190044.jpg and


Parts cleaned first in paraffin, then petrol, then finally brake cleaner. Compressed air inbetween. There are gaps between when I can work on it so the bits are stored in some plastic boxes, and the block wrapped in a large plastic bag.

IMG_20240209_190026.jpg and
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PostPost by: rgh0 » Sat Feb 10, 2024 11:22 am

ill_will wrote:Does anyone have any advice on what to use to oil the bores if the engine might sit for a while before being run, but that doesn't affect bedding in the new rings when it is run-in? I've used ATF for the moment, but not sure if that's a good choice.


I normally use WD-40 and respray the engine when i turn it over every couple of months

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PostPost by: ill_will » Sat Feb 10, 2024 11:48 am

rgh0 wrote:
ill_will wrote:Does anyone have any advice on what to use to oil the bores if the engine might sit for a while before being run, but that doesn't affect bedding in the new rings when it is run-in? I've used ATF for the moment, but not sure if that's a good choice.


I normally use WD-40 and respray the engine when i turn it over every couple of months

cheers
Rohan


Thanks
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