twin cam questions

[johnd]

Hi all

This is my first post on this forum so I hope its in the right place!

Also I own a 1969 Lotus Cortina so maybe I'm supposed to go to the black label section (as a little perverted). I'm also in Perth Western Australia.

However:

I'm hoping some mechanical gurus can give me some advice:-
I have a 1973 build "L" block engine with a standard bottom end.
I've had a drama with bent valves on my twin cam and now the engine is apart I've discovered that my head is a sprint head with double valve springs, high lift cams and larger valves. The head is down at the shop now being fitted up. A couple of questions for the gurus:
- The guy building the head says the engines he builds (mostly track engines) never have oil seals on the valve stems (above the guides) as the valves on these engines should run a little ?lubricated? on unleaded petrol (even though the valve stems in my head are supposed to be suitable for unleaded use) ? your thoughts??
- The block will get a make over to smarten it up which will mean new 030/040 pistons. The crank is currently 010 oversize and a light polish will allow it to remain 010 with new bearing shells. 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
- Since I have a ?big valve? head do the pistons need to be designed for use with this head ? my original ones were not ? they were standard cut outs. Once again advice please?

[ardee_selby]

Greetings John,

This is my first post on this forum so I hope its in the right place!

Spot on! "The Technical" & "Things in common".

A couple of threads relating to valve stem seals & pistons:

elan-mods-f31/valve-stem-seals-twincam-t22748.html
elan-f15/piston-query-t24399.html

Valve stem seals? A solution to a problem which might be worsened by their presence by reducing lubrication?

Piston choice? See users experiences (re: cast-v-forged) in above thread. Horses for courses? You pays your money etc...but look out for valve/piston clearances.

I imagine the guru's will be along to add more shortly, but hope my 2 penn'orth will kick the thread off OK.

Cheers - Richard

("a little perverted. I'm also in Perth Western Australia" )

[johnd]

thanks Richard, I've had a quick look at the links (funny I couldn't find them when I searched ????). Definitely some food for thought.
I'm hoping someone adds more about the old/new technology pistons and rings though.

jd

[1964 S1]

I'll add...

I've found throughout my life that new technology is better. (...until I drive my Elan.)

Thank you Colin and Ron.

ps; I'd go with the "newer" pistons...

[johnd]

Thanks for that comment - have you had any experience with modern piston selection for these motors? (This is a road car and is not being built for track work so cost - effective solutions are being sought)

jd

[StressCraxx]

If your car is road use only, then no worries with the Hepolites as long as the valves clear the pistons properly. I have the big valves, sprint cams and the later Hepolites with the deeper reliefs. They work just fine for road use. Pistons have been in the car since 1982 with one ring job.

Check clearance with modelers clay on top of the piston at tdc. Install the head with an old gasket and rotate the cams carefully with the intake and exhaust valves fully open. Pull the head and use a depth gage or scale to see how thick the clay is. If you see metal, then the valve cut outs in the pistons need to be cut. I don't recall the minimum clearance, but someone will chime in.

Regards,
Dan Wise

[types26/36]

I don't recall the minimum clearance, but someone will chime in.

60 thou or an ABSOLUTE minimum of 40thou.

[Tonyw]

John,

These cars went well with the "old" technology pistons so I cannot see that there is much advantage in changing for the newer type unless you have an idea that you might do a squillion miles!!! I also think that as the L blocks are becoming rare it is wise to minimise the amount you bore the block, that way you can keep it much longer before you need to sleeve it.

I hope to see you at the Gin Gin all British car day this year, give me a call if you feel like a chat and swap notes, I am in Mundaring, 0417 555 073

Tony W

[Elan45]

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

[ardee_selby]

<snip> 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...<snip>

Roger, Guys,

And if the valve timing is being done!

This little "snippet" has stuck with me since I read it all those years ago. An example where the guy had checked clearances and THEN timed (degreed) them!

(From elan-f15/one-man-his-twink-from-1985-t23399.html)

Richard

[billwill]

I have a piston here which I keep as a reminder of my young ignorant days.

I reassembled the engine without understanding at all about the settings of the camshaft (previously I had only dealt with two strokes & weak engines where there was nothing to overlap).

Amazingly the engine started, but made the most amazing banging noises before it stopped.

On dismantling I found one valve snapped off, & several bent ones. The snapped valve had rattled around, getting on edge & cutting deep grooves in the head, the valve seats and the top of the piston. Eventually it had become vertical with the short broken valve stem downwards and the piston had driven itself upwards onto the stem, piercing a hole in the top of the piston, which is where I found it, looking like a mushroom, when I took the head off again.

That was one very expensive mistake!!!




PS: I dunno why we have factory instructions & timing marks which set the cams at top dead centre, it would be much safer if the techniques had been respecified and sprockets marked to be aligned with all the pistons at equal level at "half-mast".

[Elanintheforest]

Hi John, and welcome to the other side!!

Get your head man to check the thickness of the head as well, just for peace of mind if nothing else. Small Valve = 4.638/4.643" with another .045" allowed to be removed. Big Valve = 4.598/4.603" with only another .010" allowed to be removed.

I hope you're getting used to not sorting out those cattle guys every day now!

Mark

[rgh0]

Hi Mark

You can actually remove a lot more material than the Lotus quoted 40 thou for a standard head and 10 thou for a Big Valve head without major problems

Hi John
The advice posted so far covers the topic very well
i.e

No need for valve guide seals if stem to guide clearances set right

QED pistons and older style cast pistons and rings fine for a road car if building to a budget.

I use JE forged pistons with modern lightweight ring packs in the engines I build but most of these are race motors and the pistons are not cheap

But do check clearances on assembly as many mods tend to have been done to these engines over the years and clearance may not be standard due to think head and short blocks and vlavles set in wrong postion in head etc.

If possible you should get the block ultrasonically checked and offset bored to maximise the wall thickness when you take it out to plus 30 thou so you have enough wall left for another 10 thou on the next rebuild


cheers
Rohan





cheers
Rohan

[johnd]

Guys
I have been overwhelmed with the speed and detail of your combined assistance - a genuine "thank you" to all.

Mark - I should have known you'd have a dark side !!!!!

Richard that article looks really interesting - I followed the link but cant get it clear enough to read can you point me to the original source please?

Tony - I've only recently joined the real world (retired) after too many years at airports and in planes - what is happening at Gin Gin and when?

I have learned heaps from your comments and, although I'm not a total mechanical novice, the twin cam engine is new to me and my engine is (was) an unknown quantity.

best regards and thanks to all

jd

[ardee_selby]

Guys, I have been overwhelmed with the speed and detail of your combined assistance - a genuine "thank you" to all

If Carlsberg did internet forums...

Richard that article looks really interesting - I followed the link but cant get it clear enough to read can you point me to the original source please?

Sorry John, they weren't the best quality scans & were done a while back when space was at a premium.

Could you try this:

1.0 Right click on the chosen image (in this case page) and select "Open link in New Tab" or "Open link in New Window".

2.0 When opened, pass the mouse cursor over it. It should turn into a "+". A click of the mouse and it should expand it.

3.0 Right clicking on it again will give the option to "Save Picture As".

Let me know if that works OK for you. (I could do a better set of scans if not, but note that it is an old account)

Cheers - Richard