Lotus Elan

shortened jackshaft

PostPost by: tonyabacus » Wed Jan 12, 2022 12:40 pm

Thinking of fitting a shortened jackshaft to an engine I am building, does anyone have experience of fitting or know of any issues in doing such a fit
Tony
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PostPost by: seniorchristo » Thu Jan 13, 2022 12:45 am

I did it on a recent engine rebuild. Be sure to rotate rear cam bearing to contain oil flow.
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PostPost by: rgh0 » Thu Jan 13, 2022 2:36 am

Some people have had problems with the steel shortened shafts sold by some of the suppliers not being straight and binding in the bearings or thrust plate. I have used a couple and they have been Ok but maybe I was lucky. I have also cut and shortened the standard cast iron shafts with no specific issues.

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PostPost by: HCA » Thu Jan 13, 2022 2:29 pm

This was going to be a pm question to you Rohan at some stage - is there any benefit of having a long shaft? They are both the same price from QED, and as I will never use the mechanical fuel pump, and to save on having the pump cam sloshing oil into the head drain hole, I was going to spec a short shaft. Correct?

In fact, on the subject - do you know if Trikbits or anyone is actually making these drain modifications??
http://elantrikbits.com/lotus-elan-blog ... iner-tube/
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PostPost by: pharriso » Thu Jan 13, 2022 2:59 pm

HCA wrote:In fact, on the subject - do you know if Trikbits or anyone is actually making these drain modifications??
http://elantrikbits.com/lotus-elan-blog ... iner-tube/


Hal, I bought the Aluminium drain tube from Lotus Marques in Austrailia (On https://lotusmarques.com/parts/catalogue/lotus/54-ford-performance-parts/1414-twin-cam-engine-parts-3) & I can heartily recommend it!
IMG_2365.jpg and

Shipping was also fast to the US.
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PostPost by: HCA » Thu Jan 13, 2022 3:08 pm

Thanks Phil - these seem quite delicate to put in though, are they? The trikbits idea, to me anyway, seems simpler as the length is adjusted after the head is tightened down, whereas Lotusmarques, it appears you have to get the height correct before installing the head...maybe I misinterpret though?
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PostPost by: pharriso » Thu Jan 13, 2022 3:22 pm

HCA wrote:Thanks Phil - these seem quite delicate to put in though, are they? The trikbits idea, to me anyway, seems simpler as the length is adjusted after the head is tightened down, whereas Lotusmarques, it appears you have to get the height correct before installing the head...maybe I misinterpret though?

No, It's really easy, I tapped it in with a rubber mallet. I went with the traditional head assembly method with 2 dowels (old cylinder head bolts).

I've attached the instruction sheet.
LotusMarques_ twin cam alloy breather tube.pdf
(95.3 KiB) Downloaded 42 times
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PostPost by: HCA » Thu Jan 13, 2022 6:05 pm

I can see how the bottom design is good and should never leak, but the upper entry - is this reliant on the 'O' ring sliding into the head to make a seal, or is there also an 'O' ring between the bottom face of the cylinder head and the upper step of the drain tube?

How long have you had yours in place? Is it totally dry in that area?
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PostPost by: HCA » Thu Jan 13, 2022 6:26 pm

Idling away some time and pondering on the subject, I uncovered this as an alternative..!

viewtopic.php?f=50&t=46831
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PostPost by: 2cams70 » Fri Jan 14, 2022 11:17 pm

I’ve used the Lotus Marques breather tube and it’s great. Simple. The other alternative has way too many O-rings and parts. One thing you do need to watch though is that the breather hole machined into the head is only rough machined and doesn’t have a smooth surface as it was not originally designed to accept an O-ring. As Lotus Marques point out you must therefore use some silicone sealant around this area on the O-ring to assist the seal. Threebond 1217H silicone is ideal here. It’s what OEM’s use in engines and is the right consistency. Although it’s not 100% design correct to use silicone to assist an O-ring it’s an ok solution here!

As for the jackshaft I very much doubt whether it has any affect on oil leakage here. Note that the aftermarket jack shafts all have the single round groove provision on the front journal for head lubrication rather than the 4 slots used by the original. Only BDA’s used the single round groove and in these engines a restrictor was used between the block and head to reduce the oil flow. I prefer the 4 slots as per original. I suspect if you use the single groove type and especially without a restrictor you’ll get too much oil flow into the head
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PostPost by: greg40green » Sun Jan 16, 2022 12:07 am

tonyabacus wrote:Thinking of fitting a shortened jackshaft to an engine I am building, does anyone have experience of fitting or know of any issues in doing such a fit
Tony

What possible benefit can be gained from shortening your Jackshaft , What are you trying to achieve ?
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PostPost by: h20hamelan » Sun Jan 16, 2022 5:35 am

Do people use a upside down cam bearing, to reduce friction?
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PostPost by: ajwheels » Sun Jan 16, 2022 6:46 pm

greg40green wrote: What possible benefit can be gained from shortening your Jackshaft , What are you trying to achieve ?


Adding lightness?.... :lol: .....I too wonder at the benefit.....frictional losses must be minimal......
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PostPost by: bitsobrits » Mon Jan 17, 2022 12:50 am

greg40green wrote:
tonyabacus wrote:Thinking of fitting a shortened jackshaft to an engine I am building, does anyone have experience of fitting or know of any issues in doing such a fit
Tony

What possible benefit can be gained from shortening your Jackshaft , What are you trying to achieve ?


Free horsepower for one thing. Less rotating mass to accelerate and all that. Of course the amount of power gained would be very small given the small amount of weight saved and it's small radius, but it's free!

I cut down the standard shaft on my last build (and installed the rear, unused, bearing to block the oil hole-don't forget this!) and it made absolutely no discernible difference on my street engine. But it seemed a very Lotus thing to do.
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PostPost by: cabc26b » Mon Jan 17, 2022 11:25 pm

I have used a shorten jack shaft on a race engine . no issues
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