Lotus Elan

Oh dear, what has been done to my cylinder head...

PostPost by: benymazz » Sun Oct 06, 2019 11:43 pm

A valve and valve guide replacement on my head has turned into opening up a whole 'nother can of worms!

I dropped the head off at my machinist to have the valves and guides replaced. A couple of days later I got a call saying that one of the sleeves for the exhaust tappets (no. 2 cylinder) was very loose and had some, erm, mechanical damage where there was, let's say, uh, "carnal knowledge" between the cast iron sleeve and the camshaft lobe. There was no visible damage to the camshaft lobe but there was clear damage to the sleeve (this explains the metal grit I found in my oil pan when I stripped the rest of the engine down - never good!).

I had the bottom end of the engine apart just 20 miles ago - it is stripped down again due to me being bad at reading tolerances and reusing some pistons that should have been replaced. I do know for a fact though that there was no damage to the sleeve when I put the engine together 20 miles ago as I did a through visual inspection of the head. So now, as part of my slightly annoyed at myself "pulling out all the stops" attitude I'm also rebuilding the head at the same time. Which is how we got here.

Upon further inspection though it appears that this is even worse than it looks and I am confused. I can't eloquently put this into paragraph form, so here is a list of observations:
1. The measured OD of the cast iron sleeve is approximately .005-.007" SMALLER than what is specified for the OD (as listed both in my workshop manual and the Dave Bean catalog)
2. It appears that the side of the sleeve and the head were drilled into after the sleeve had been fitted, cutting into both at the same time, and then the hole was tapped and a small screw was installed, almost acting as a roll pin of sorts.
3. No other sleeves have any indication of looseness or movement.
4. The exhaust valve guides had been knurled previously (don't attack me - I didn't do it!), and also had excessive wear. I guess this explains why I had such awful symptoms of worn exhaust guides.
5. Each of the exhaust guides had what looked like a small chip taken off of the top of them near the side closest to the spark plugs. I have no idea what this is from but it must have been intentional because it's the exact same size and in the exact same place on all 4 of the guides.
6. There are lots of punch marks around the tops of the tappet areas in the aluminum of the head.

The best conjecture I can make is that undersized sleeves were deliberately used due to not being able to get the correct size for replacement at some point in the past but something still seems fishy. Also the cutouts in the valve guides puzzle me.

See attached pictures for details.

Thanks,
Ben
Attachments
img_0003.jpg and
img_9997.jpg and
img_0001.jpg and
1965 S2 26/4623
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PostPost by: rgh0 » Mon Oct 07, 2019 9:59 am

Were the bucket followers the correct diameter or were they larger. i have heard of Alfa buckets being used and maybe they have used Alfa sleeves also. i have seen loose sleeves rotate in the head and the cam chew out the edge of the cutout like yours. Given the poor work on the sleeves the guides are probably not original and may have come from an engine that used the cutout to locate a valve stem seal.

The dimples are a poor attempt to shrink the diameter of the sleeve bore to fit the loose sleeves tighter

All told i would take the head back to a bare casting and replace everything ( guides,seats sleeves) back to original specification or over size if required for correct fit. I would trust nothing with the current interference fit components on the head

cheers
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PostPost by: nmauduit » Tue Oct 08, 2019 8:29 am

The issue of lose bucket sleeve was probably not new since set screws were used which is not stock (though I believe racers would implement that kind of insurance against sleeve rotation).

fwiw one can get oversize buckets, e.g. from QED 5thou oversize (no affiliation) :

https://qedmotorsport.co.uk/qed-shop/lo ... dard/0-005
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PostPost by: 2cams70 » Tue Oct 08, 2019 10:03 am

What is the actual measured OD of the sleeves? This will determine whether or not they are already oversize.
If they are already oversize it may be problematic because custom sleeves will be required. Same with the guides.
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PostPost by: rgh0 » Tue Oct 08, 2019 10:07 am

nmauduit wrote:The issue of lose bucket sleeve was probably not new since set screws were used which is not stock (though I believe racers would implement that kind of insurance against sleeve rotation).

fwiw one can get oversize buckets, e.g. from QED 5thou oversize (no affiliation) :

https://qedmotorsport.co.uk/qed-shop/lo ... dard/0-005



Only dodgy or ignorant racing or road engine builders would use a a screw to prevent sleeve rotation versus the proper interference fit. If your head is getting so hot your losing the interference then you have other problems you need to fix.

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PostPost by: nmauduit » Tue Oct 08, 2019 10:39 am

rgh0 wrote:Only dodgy or ignorant racing or road engine builders would use a a screw to prevent sleeve rotation versus the proper interference fit. If your head is getting so hot your losing the interference then you have other problems you need to fix.


yet I've also seen similar approches (screwed on bracket to press the bucket sleeve down) on rather expensive 3.8l Jag race engines... I guess the rationale is damage control when things go wrong.
Last edited by nmauduit on Tue Oct 08, 2019 3:07 pm, edited 1 time in total.
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PostPost by: Elanman99 » Tue Oct 08, 2019 12:36 pm

rgh0 wrote:
nmauduit wrote:The issue of lose bucket sleeve was probably not new since set screws were used which is not stock (though I believe racers would implement that kind of insurance against sleeve rotation).

fwiw one can get oversize buckets, e.g. from QED 5thou oversize (no affiliation) :

https://qedmotorsport.co.uk/qed-shop/lo ... dard/0-005



Only dodgy or ignorant racing or road engine builders would use a a screw to prevent sleeve rotation versus the proper interference fit. If your head is getting so hot your losing the interference then you have other problems you need to fix.

cheers
Rohan


I agree totally with your first sentence but the second one infers the problem is because the head is getting too hot, in reality its the shoddy engineering and incorrect interference.

Ian
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PostPost by: rgh0 » Wed Oct 09, 2019 8:58 am

Elanman99 wrote:
rgh0 wrote:
nmauduit wrote:The issue of lose bucket sleeve was probably not new since set screws were used which is not stock (though I believe racers would implement that kind of insurance against sleeve rotation).

fwiw one can get oversize buckets, e.g. from QED 5thou oversize (no affiliation) :

https://qedmotorsport.co.uk/qed-shop/lo ... dard/0-005



Only dodgy or ignorant racing or road engine builders would use a a screw to prevent sleeve rotation versus the proper interference fit. If your head is getting so hot your losing the interference then you have other problems you need to fix.

cheers
Rohan


I agree totally with your first sentence but the second one infers the problem is because the head is getting too hot, in reality its the shoddy engineering and incorrect interference.

Ian


Hi Ian, my second sentence was around race engine builders using this pinning technique when they have the correct interference fit, It is done by some because in racing the head temperatures can get high if the engine cooling has not been sorted resulting in the sleeves coming loose and rotating. As you observe overheating was not the cause of this sleeve being loose but rather it was bad fit in the first place.
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Rohan
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PostPost by: potleyu18 » Wed Oct 09, 2019 3:39 pm

You could try CTM engineering as i have seen a far worse head damage they repaired and it was almost impossible to see the area of repair afterwards.

They have recently carried out major overhaul of my Plus 2 head and re-bore and pressure test of the block. all to an exceptionally high standard.

email [email protected]

Tel 020 8592 1180

Steve
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