• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Valve lash

Share this page

OP
TomMull

TomMull

Darth Vader
Bronze
Country flag
Offline
This seems curious. I took my Plus 2 S engine apart for evaluation and checked valve lash. The intake measured .007 on all 4 which seemed good to me. But when I measured the exhaust I found they were consistent but at .014. (Spec is .005 to .007 for intake and .009 to ,011 for exhaust).
The consistency is the curious part, it doesn't seem that they would wear that evenly. This is my first lotus twin cam so perhaps they do. Otherwise is there a reason someone might have purposely increase the gap on the exhaust valves?

My plan is to re-shim the exhaust ones at .010 and leave the intakes as is.

Tom
 
Sort by date Sort by votes
Hi Tom,
Apparently not too many here are Twink owners. The lash opening evenly like that is odd, and it may speak to wear or as you say, simply set too large. Are the cams original grind? With calipers you can measure the lift roughly with just removing the cam cover. also check the number of rings on the front of the cams. Should be SE cams I think, but may be Sprint versions, if not reground to something else, which is very common. Re-shimming back to stock is good as long as you can verify the grind is stock. Have you the Miles Wilkens book on this engine?? Worth every dime.
Jerry Rude
Europa TCS 4005R
 
Upvote 0 Downvote
Thanks Jerry, the deeper I got the worse it got. I found the raised bump on the bottom of the cam followers (buckets) had been ground away as well as two of the retainers. I can only assume that the valve tips had been ground also but I didn't bother to measure them.

I sent the whole mess to my local machinist along valves, seats, and buckets from Ray at RD Enterprises and found a friend with a collection of shims from Triumphs and set the lash myself. I did not measure the cams.

I'll look for the Miles Wilkins book also.

Tom
 
Upvote 0 Downvote
Tom, Has your “local machinistl had experience with Twinks? The reason I ask is that more damage has been done to these engines by well meaning machinists than on any other engine that I have had experience with. I am currently helping a friend who did the same as you, unknowingly having his engine rebuilt by people who had no business attempting it.
Jerry
 
Upvote 0 Downvote
I know what you're saying Jerry but I'm fairly confident with their work. I gave them the specs from the Factory Manual and everything seems correct and consistent. Other make twin cams are now common and they had a bunch of them. Will post if I find otherwise.
 
Upvote 0 Downvote
Tom,
I hope they can do a proper job. You might want to have them check a few items which a twink experienced shop would: Softening of the head due to overheating (recessed valve seats, head bolt hole top surfaces recessed, warpage), Valve guide clearances per manual since the valve guides are so short and with no seals clearance is critical, spring seat machining for larger springs, welding done in past, cam bores being true, and honing them straight, bucket clearances within spec and if not replacing the liners, etc. Since its a weber head, it is likely that it has been worked on a number of times and that it has been modified in some way. Also, if it is a really early head, the oil drain back may be restricted on the exhaust side, and perhaps something could be done about it.

I would also suggest that you join www.LotusElan.net based in the UK. There is a bunch of info on there along with many experts on the twink.

When I was overhauling my twink (stromberg big valve), I took the block to a local machinist simply because the owner used to race a Lotus 51B, which came with a twink. He would machine the block for me (hone, liner, skim the head surface), but he wouldn't touch the head even though he worked on newer twin cams like Honda, etc. He recommended a local race shop owned by an ex Indy crew chief. He had done Lotus heads before and it came back looking really nice (took him 6 months though). All shims were within .001 of each other, amazing. The head is still running and not smoking after 38k miles.

Best of luck, Jerry
 
Upvote 0 Downvote
Good information Jerry but kind of after the fact at this point. Head is done, shims quite consistent, obvious issues corrected and hope for the best.

Also good to have some Lotus activity on this forum too.

Tom
 
Upvote 0 Downvote
Jerry,
I did join the British net. The were very helpful getting Vin numbers sorted and a build record sourced for my plus 2S.
Thanks,
Tom
 
Upvote 0 Downvote
Back
Top