twin cam questions

[AHM]

However I?m told that modern pistons (and rings) are vastly superior in ring design and piston lubrication to the original designs. As modern pistons only come in 020/040/060 sizes this would mean taking my bore out to 040 instead of the more minimal 030. I can get original pistons in 030 oversize from QED ? should I do the minimum oversize on bores (and use 030 pistons and rings but "antique technology") or go modern and accept 040 oversize - advice please

What is "antique technology" about QED pistons? I suggest that you call QED and discuss.

[jimj]

Related to this and AHM`s question about valve seats: Last year I lost compression on one cylinder and on removing the head found one of the valve seats had bizarre damage, as if something really hard had been crushed between the seat and the valve, about half the size of a match head. I was recommended to take the head to a diesel engine rebuilder in Chesterfield by someone I respect. They offered to recut all the seats for something like ?2.40 per seat. I couldn`t believe it but they seemed to know all about......well....everything, but that`s just compared to me. Anyway I had the head all checked and rebuilt by them at a total cost of, I think, around ?190, so it was just a question of putting the head back on.
I`m sure this is not my imagination but the car, which went well before, absolutely flies now. I`ve done around 2000 miles since and all is well.......but......I do get much more smoke after a period on overrun which suggests more oil being sucked down the valve stems. So, how close is "nuff"?
Jim

[ardee_selby]

<snip> I`ve done around 2000 miles since and all is well.......but......I do get much more smoke after a period on overrun which suggests more oil being sucked down the valve stems. So, how close is "nuff"? Jim

Jim,

Having followed Petes' saga of his loose valve guide, I made a note of the following paragraph for future reference:

"I presume you have fitted bronze guides. When reaming the guides aim for the tight end of the lotus spec clearance range for the inlets to minimise oil leakage down the guides. Aim for mid range on the exhausts as oil leakage less critical and you want to avoid binding due to the greater valve stem expansion on the exhaust. If using the original style cast iron guides aim for midrange on both".

(Ref: elan-f15/loose-valve-guide-t22263-45.html)

My Lotus manual gives:

Stem clearance in guide - INLETS 0.0003" / 0.0023"
Stem clearance in guide - EXHAUST 0.0025" / 0.0030"

Cheers - Richard

[johnd]

In relation to AHM's query - the words "antique technology" are the engine shop's view of old design pistons and rings - not mine!

jd

[AHM]

John,

Last year I did some research into twincam pistons. I don't think that oversize cast pistons are available, so in terms of their material properties they are better than original. I couldn't find any problems that people had had other than the valve cut-outs mentioned earlier. Again I don't think you will be able to find new pistons with the small cut-outs. I believe that the small cut-outs were the later type anyway so even if you could find some there shouldn't be a problem.


Other than the wheel bearings and light bulbs I can't think of anything on the Elan that is current production standard. The design, materials and manufacturing methods are all 50 years old, so it is all getting on for antique. I'd be cautious of anyone suggesting new improved this or that, not because I think thEm to be wrong, but because it gets a lot more expensive.

The advice about the valve guides is good. The only other thing I would add is that getting the engine balanced is much recommended.

Simon

[StressCraxx]

I agree with your head man. No need for stem seals if the guides/ stems are up to snuf. I too would use the old Hepolite pistons. They are just fine. No need to bore the block unless the bores are oval or tapered.

I have to disagree about claying the engine to check valve clearance. Do NOT just rotate the cams with pistons at TDC. They will touch and you may damage the valves or pistons.

The intake valves will open just before the piston reaches TDC, but will only be open just a little bit. It will not be fully open until the piston is halfway down down the bore.

After firing and power stroke, the exhaust valve will begin opening just before BDC, be fully open as the piston is about half way up the bore. It will still be open a little bit as the piston approaches TDC.

So, to clay the engine, you must assemble the engine with the old bearings and no rings. Don't bother to torque things or stretch the rod bolts. You want things snug, but not tight-tight. Use the old headgasket as someone else suggested.

If you are not going to degree in the cams, make sure you at least have the intake and exhaust sprockets on the right cams and set to factory marks. The sprockets are marked "INT" and "EX". You will need to remove the head to check the clay blobs, so you might want to use only 4 head bolts at first for this checking process. If you leave the cams in the head, be very careful that you do not sit the head down on the bench with the valves extended. I like to work on the head with it sitting on the front timing chest.
Always turn the engine to TDC before you remove the head!!!!!

This way, the cams should be on their marks and the crank is also on its mark.

Be very careful! Don't force anything! Good luck.

Roger

Roger,
Thank you for correcting me. I should have proofread my own post. Sorry to cause confusion or poor advice. I do advocate degreeing in the cams, especially if the head or block mating surfaced have been machined. I found my intake cam was opening almost 4 degrees late. It made quite a difference in driveability in my twink.

Regards,
Dan