Lotus Elan

Twin Cam Camshafts and Cam Cover....

PostPost by: Phil.C60 » Tue Jan 24, 2023 7:48 am

Hello all, here we go again I'm afraid, but I've looked and looked and I can't find the answer.
My Elan is (or was originally...) a 1971 Elan Sprint. It came to me spring last year having stood for some time and I have done a lot of the usual things to get it back on the road - Rotoflexes, front calipers, clutch cylinders Coolex rad with extra row and modern fan, new temp gauge (gen. Caerbont), new recuperator bottle (it was missing), correct type rad cap (7lb) etc etc. and I have been driving it around this last summer.
It has an issue with 2nd gear synchro, the clutch judders a bit in reverse when hot, so engine and box is now out and gearbox is away for repair.
It has always run a tad warm (82* stat fitted fresh coolant), especially when pushed a bit hard and has all the usual oil leaks so the plan is to remove head/sump etc, and check the head gasket, water pump clearance/impeller etc and the block for sludge/sand.
So far, so good.
I've had a look around and the following is the case.
Cams are .375 total lift (measuring the cam lobes so no allowance for valve clearances as they are all over the place at present) and have two rings behind the sprockets.
The cam cover is red, does not have two half moons at the back, it has one half moon and one round plastic plug with a brass locating peg where the tit on the half moon would be, ie there is a half moon cut out in the cam cover as well as the head in one corner. These were both slightly loose before undoing the cam cover nuts so no surprise it leaked.
The flywheel has timing marks on it.
I'm thinking that it's had some Europa parts used at some time!
Any thoughts from anyone re all that and the cams?
Thanks all,
Phil
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PostPost by: 2cams70 » Tue Jan 24, 2023 8:40 am

It always amazes me this paranoia about the engine temperature gauge. There’s good reasons why a lot of manufacturers these days don’t bother fitting them. The maximum coolant temperature is determined by the radiator cap. If the cap fitted is of the correct OEM pressure rating, the cooling system is full with coolant and coolant is not escaping down the overflow pipe the coolant temperature is within design specification.
The coolant gauge is useful for monitoring any sudden change in what is normal but not all that useful in determining absolutes.
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PostPost by: gjz30075 » Tue Jan 24, 2023 9:08 am

Make sure to get the flywheel resurfaced because I'm sure you'll be fitting a new clutch disc.
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PostPost by: rgh0 » Tue Jan 24, 2023 9:55 am

it sounds like the cams started life as Sprint cams with the 2 rings and 0.360 lift but have been reground at some stage for 0.375 lift. lookfor some making or stamping on the cam front that the cam regrinder may have done.

I dont know what runing "a tad warm means" but running lean or with to much ignition advance can push up the operating temperature a little but I would also check or replace the thermostat.

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PostPost by: Phil.C60 » Tue Jan 24, 2023 10:09 am

I should have been more specific....it rises to around 88 and then 94/5 when pushed but but no means flogged. Radiator lower deflector is in place and foam strip too. I can't seem to find out for sure if the cam lift is 360 at the bucket which would be minus 10 thou so 365 actual? That would be pretty close to the correct sprint lift
I'm checking the duration as we speak before taking the head off and I'll check that at 10 thou lift at the lobe.
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PostPost by: rgh0 » Tue Jan 24, 2023 10:40 am

Sprint cam lobe lift above base circle is 0.360 inch so follower lift is that less the clearance setting. If you have accurately measured lobe lift at 0.375 then the cam has been reground.

I would not be overly concerned at those temperatures if not loosing coolant and I would replace the thermostat and make sure no air in the ssystem before pulling off the head

cheers
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PostPost by: 2cams70 » Tue Jan 24, 2023 11:16 am

If you are going to replace the thermostat use one with the original specification temperature rating. Don’t be tempted to fit one with a lower temperature rating or remove the thermostat altogether. It will not reduce the maximum engine temperature but merely serve to prolong the warmup period which will result in increased cylinder bore wear.
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PostPost by: Craven » Tue Jan 24, 2023 12:20 pm

From a recent and interesting contribution by Rohan on here “The base circle on the sprint cam I measured was the standard 1.15 in / 29.21 mm” this will be less on your cam if reground to give the 0.375” lift.
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PostPost by: Phil.C60 » Tue Jan 24, 2023 2:10 pm

Thanks all. I did measure the base circle and lobe, deducted on from 'tother and that's what the lift figure was. I'll check the base circle tomorrow - I'm back at home now.
Head is now off, inlet valves are 1.604". Exhausts are standard 1.326". That's rough of course, as the valves are still in the head but I'm certainly not 1mm out and the exhausts are spot on size. My hands aren't that shaky. And two of us have checked them.
Cam timing at 50thou lift is: Inlet opens 30* before TDC, closes 117* before TDC. Exhaust opens 116* before TDC, closes 22* after TDC. No verniers: marks on sprockets align as they should.
That's allowing for the valve clearance as measured on the lobes used for clocking.
Head has been clearly been ported, I haven't checked the head thickness yet, it has flat top pistons and it is clearly running rich despite having a brand new set of 40dcoe151 correctly jetted and float height set (or so I was told by the supplier....we'll see) and choked at 30mm (well i had to start somewhere, and following the comments about low down driveability issues with 32/33 mm chokes that's what I asked for). I now have a set of DCOE 31's with 33mm chokes to be rebuilt as an option.
Onwards.
All comments/info welcome.
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PostPost by: Phil.C60 » Thu Jan 26, 2023 5:25 pm

Well, a further update.....having rechecked my cam figures and found was definitely somewhere near right so I took the cams to Newman Cams today and Ken checked them properly. They are both identical. They have either been ground from old blanks or reprofiled, but are ground well in his opinion and they have no discernible wear. I undercalculated the lift, it's actually ,385" and the duration is......312*. Huge.
Only really suitable for a race engine. He is going to make me a pair of cams with .380" lift and 280* duration, with base circles to match my current size so that the shim ranges will be close to my existing and I should be able to get a clearance of some sort to start with and work from there.
Any bids on a set of race cams for a Twin Cam!
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PostPost by: rgh0 » Fri Jan 27, 2023 12:03 pm

The cams sound like an L2 cam grind. This was a very early race cam used when they had not figured out how to get higher lift . Later used as a cheap hot up cam in road engines when people just wanted a cam swap without rebuilding the entire head. All top end and no midrange torque so a pig on the road.

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PostPost by: Phil.C60 » Fri Jan 27, 2023 12:34 pm

Thanks for your input Rohan. I suspect that you are right, although the head has clearly been ported and has 1.6" inlet valves soo has had some work. It may even just be poor cam choice! I always thought it was a bit flat, especially having dropped the choke sizes to 30mm when fitting the 151s. The rest of the internals are good, bore size is spot on plus 40 and the crank is fine too at 10/10. Water pump is good, no signs of leakage and no corrosion of the sleeve or front cover. Clutch is knackered so that, bearings, a chain for good measure, core plugs to clean out the water jacket and a careful reassembly should be good to go for the summer....
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