Lotus Elan

Camshaft help

PostPost by: Andy8421 » Sat Jul 30, 2022 11:06 am

I am stripping down the engine from my Sprint. There engine has clearly been tuned, and it has been suggested the engine was fitted with L1 cams. I am a believer in trying to figure out what I am dealing with before I strip it down, so with the help of Youtube, I have taught myself about cam timing. Its a PITA.

I checked the clearances first and got.

Exhaust
1 - 0.004"
2 - 0.014"
3 - 0.013"
4 - 0.008"

Inlet
1 - no clearance
2 - 0.001"
3 - no clearance
4 - 0.003"

I measured the cams - they have a base circle diameter of 24.25mm and lift of 10.58mm (0.42"). The cams are marked VJ5 - which a bit of digging indicates they are Vegantune camshafts.

IMG_3061 - Copy.jpg and
Cam timing disc


IMG_3062 - Copy.jpg and
Dial gauge



I messed around for ages measuring the timing. As best as I can figure, the Exhaust MOP is 105 degrees BTDC, the inlet MOP is 118 degrees ATDC. Measured duration is a very approximate 280 degrees.

The only info I could find on the cam on the web indicates that the cams should be timed to have an Exhaust MOP 110 degrees BTDC, inlet 105 degrees ATDC. Rohan's very helpful post on cams suggests that cams with 280 to 290 duration and lifts in the 0.40 to 0.44 range should have MOPs of 108 to 106 degrees, so the data I found on the web for the cam looks about right. The engine as set up currently is however a complete dog's breakfast.

I intend to rebuild the engine completely. Are my VJ5 cams a jewel worth persevering with? or should I mount them on the garage wall and buy modern known quantity camshafts?

Thanks as always for any feedback.
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PostPost by: promotor » Sat Jul 30, 2022 11:24 am

KC VJ5 cam specs given to me by Kent cams are as follows (this is their version of the Vegantune cam, which as far as I'm aware is identical) :
Lift 0.350"
Duration 260 degrees (no details of whether this is @ 0.050" checking height, but it would make sense, given how short the quoted duration is).
MOP 108 degrees
0.010" clearance.

If that's correct, then perhaps your cams were either reprofiled using a cam that was a VJ5, or Vegantune VJ5 are different to Kent Cams VJ5, which Kent Cams didn't advise me that was the case.

The base circle you have mentioned is quite small - I've never seen any that small, but that doesn't mean they don't exist, just that's it's not normal practice.

How did you get the lift - did you measure cam follower movement? Or did you calculate it from length of cam minus base circle?
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PostPost by: Andy8421 » Sat Jul 30, 2022 12:07 pm

promotor wrote:The base circle you have mentioned is quite small - I've never seen any that small, but that doesn't mean they don't exist, just that's it's not normal practice.

How did you get the lift - did you measure cam follower movement? Or did you calculate it from length of cam minus base circle?

Thanks for the response.

I may well have screwed up, but I used a digital vernier caliper to measure the base circle - so it it would have been tough to have got that wrong (although not impossible).

I used length of cam minus base circle for lift, so the actual valve lift would need to have the clearance deducted from this figure.
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PostPost by: promotor » Sat Jul 30, 2022 12:28 pm

Andy8421 wrote:
promotor wrote:The base circle you have mentioned is quite small - I've never seen any that small, but that doesn't mean they don't exist, just that's it's not normal practice.

How did you get the lift - did you measure cam follower movement? Or did you calculate it from length of cam minus base circle?

Thanks for the response.

I may well have screwed up, but I used a digital vernier caliper to measure the base circle - so it it would have been tough to have got that wrong (although not impossible).

I used length of cam minus base circle for lift, so the actual valve lift would need to have the clearance deducted from this figure.


Looking at your cams they do look like they have been machined quite a lot so I would say the base circle is very small.
I would be considering the possibility that the cams aren't VJ5 specification any more!

I thought it strange that the VJ5 cam I had in my hand was only fast road spec as I was thinking the "5" possibly denoted phase 5, but that's what Kent advised.

What info have you got for the VJ5 cam? MOP figures only?
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PostPost by: 2cams70 » Sat Jul 30, 2022 12:50 pm

Those cams may have been dropped in with no cam timing done. The old sprockets could have been used and the timing done just by lining up the engraved marks. Are offset dowels fitted? If so then that’s a good sign that more care has been taken.
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PostPost by: Craven » Sat Jul 30, 2022 2:52 pm

Just from visual, turned surfaces between the cam lobes is very indicative of Vegan cams. Small base circle with this would perhaps be the grid method to get high lift from a standard cam.
Edit, They have been known to snap!!
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PostPost by: Andy8421 » Sat Jul 30, 2022 3:33 pm

2cams70 wrote:Those cams may have been dropped in with no cam timing done. The old sprockets could have been used and the timing done just by lining up the engraved marks. Are offset dowels fitted? If so then that’s a good sign that more care has been taken.

Just taken the cams out. Dowels are not offset, so it looks like the cams were just dropped in as you suspected.
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PostPost by: Andy8421 » Sat Jul 30, 2022 3:36 pm

Craven wrote:Just from visual, turned surfaces between the cam lobes is very indicative of Vegan cams. Small base circle with this would perhaps be the grid method to get high lift from a standard cam.
Edit, They have been known to snap!!

Great.

It is looking more and more like these cams will become interesting ornaments. Given the lack of definitive timing information and the chance they could snap, I think I would do better to start with a known quantity.

Thanks again to all for the very helpful comments.
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PostPost by: Andy8421 » Sat Jul 30, 2022 3:44 pm

promotor wrote:What info have you got for the VJ5 cam? MOP figures only?


Nothing definitive. Thread below makes reference to the VJ5:

https://lotuselan.net/forums/viewtopic.php?f=39&t=1788&start=

and this thread has a Vegantune spec sheet halfway down which may reference the VJ5, although as it promises 150BHP, I am not sure how reliable a source it is.

https://lotuselan.net/forums/viewtopic.php?f=39&t=19276
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PostPost by: promotor » Sat Jul 30, 2022 7:57 pm

Andy8421 wrote:
promotor wrote:What info have you got for the VJ5 cam? MOP figures only?


Nothing definitive. Thread below makes reference to the VJ5:

https://lotuselan.net/forums/viewtopic.php?f=39&t=1788&start=

and this thread has a Vegantune spec sheet halfway down which may reference the VJ5, although as it promises 150BHP, I am not sure how reliable a source it is.

https://lotuselan.net/forums/viewtopic.php?f=39&t=19276


I did a bit of research myself when this one came in an engine and as I also couldn't find anything definitive resorted to Kent Cams helpline.

Have you tried checking the duration on another lobe with clearance - exhaust number 4 is a good one to use - most aftermarket cams use 0.008"-0.010" clearance?
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PostPost by: sprintsoft » Sun Jul 31, 2022 8:56 am

Hi Andy,

I was in conversation with Tony Ingram about the VJ5 cams and he confirmed the following info to me:

=======
Hi Iain
The VJ5 is a very good profile. It was designed as a step up from the Sprint cam that gives around 5hp gain and needs no modifications to springs or piston valve reliefs.

It has 280 degrees of duration seat to seat and should be timed as follows-

Inlet fully open at 105 deg Exhaust fully open at 110 deg

Inlet clearance .006" Exhaust .010"

Jetting will vary depending what size main choke you are using.

This was always my favorite profile for a 135hp street engine.
Kind Regards,
Tony
=======
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PostPost by: rgh0 » Sun Jul 31, 2022 10:48 am

Looks like the cam has been reprofiled for higher lift and who knows what duration compared to the original VJ5. That may be good or maybe bad. If you have a local cam grinder they can measure up the profile to see what you have. The alternative is buy new cams to the profile suited your planned engine and use.

cheers
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PostPost by: Andy8421 » Sun Jul 31, 2022 5:22 pm

rgh0 wrote:Looks like the cam has been reprofiled for higher lift and who knows what duration compared to the original VJ5. That may be good or maybe bad. If you have a local cam grinder they can measure up the profile to see what you have. The alternative is buy new cams to the profile suited your planned engine and use.

cheers
Rohan

Thanks Rohan, and thanks to all the others who have responded.

I have decided to go with new cams. Trying to reverse engineer 40 year old cams from a defunct company that may have been reground to a different profile with little or no documentation feels like hard work. I now have to figure out what cams to use.

I will come back for advice when I have done some research.
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