Cam Sleeve Damage

Post by: **William2** » Sat Dec 05, 2015 5:17 pm

Having removed my cylinder head for helicoil repairs to a couple of cam cap studs, I notice that two of the cam sleeves on the exhaust side have chunks missing from the upper edges on about half the circumference. I can only assume that whoever drifted them in previously did a bodge job. Also another one hasn't been installed correctly with the scallops lining up with the head. I know this faults are not good, but is it likely to cause problems in engine performance. As you can see in the photos a good 1/8" is missing. I was hoping I could leave them as is rather than having to find machine shop to replace them and strip the head down as all the valves are fine.

Post by: **elj221c** » Sat Dec 05, 2015 6:34 pm

Sadly it would seem there has been some seriously bad 'maintainence' on your head!

Cracks seem evident around the head bolt area and serious 'undercutting' where the bolts have been overtightened.

Along with the stripped threads on the cam studs and the sleeve damage it would appear that a gorilla has been employed as a mechanic!

:roll:

It begs the question what the rest of the engine is like........

Post by: **rgh0** » Sat Dec 05, 2015 10:02 pm

I have seen similar damage but never that extensive when the cam follower sleeves have become loose in the head when its hot and moved enough to be hit by the cam lobe. Was there any sign of damage on the matching cams lobes?

I would get the head hardness tested as it looks like it has gone soft. The stripped threads, sunk head bolts and damaged cam follower sleeves all point to a head that is soft and lost strength in the metal unfortunately. Does the face of the head show an indentation where the gasket fire ring is, as this is another sign of a soft head.

cheers
Rohan

Post by: **CBUEB1771** » Sun Dec 06, 2015 3:58 am

I don't think I have ever seen a TC head with the reliefs for the cam bearing locating tabs made with a twist drill rather than the normal groove cutting tool. Is this common on early TC heads?

Post by: **rgh0** » Sun Dec 06, 2015 11:04 am

I had a look at all my spare heads and at all the photos I have of various heads from prototypes to late Big Valve that show the cam bearing tab cutouts and I cant see any with twist drilled holes for the tabs. it could be at some stage they did not mill the slots ( maybe ran out of the right cutter) or an in service modification but for what reason I have no idea.

cheers
Rohan

Post by: **William2** » Sun Dec 06, 2015 12:00 pm

It seems like my head is unusual as well!!
Here are some photos of the underside. Looks quite good to my eye. Head has been skimmed in the past and measures an acceptable 4.600". I guess I have to make a decision on whether to throw money at it or try and find another head. I think I will take it to a Twin Cam expert for advice before going any further.

Post by: **elanner** » Sun Dec 06, 2015 1:14 pm

Good grief, William, what a damn nuisance. It seems that you can't catch a break at the moment. You must be so nearly finished and now this.

I've always hated the lots-of-trouble-usually-serious moniker, but there are times when......

Anyway, all the best with this hurdle and I hope that there aren't too many more. Despite its apparent determination to make every step painful, your Elan really *does* want to be on the road! :-)

Nick

Post by: **rgh0** » Sun Dec 06, 2015 7:41 pm

Looks like some marks from the firerings also. Defintiely get it hardness tested before you put any more work into it.

cheers
Rohan

Post by: **nmauduit** » Sun Dec 06, 2015 10:36 pm

what would typically make a head go soft ? any trend from production years or something the like?

Post by: **rgh0** » Mon Dec 07, 2015 7:21 am

The head is heat treated after casting to cause it to harden from the as cast condition. Overtime time it returns to that original as cast condition. How fast it occurs depends on the actual aluminium alloy composition within the nominal specification and the time and temperature history of the head.

Lotus appear to have used LM8 and LM25 alloy in the head castings as I have seen both on cylinder heads. They are very similar in composition and properties with LM25 really just being a more recent specification. The link below gives some details on LM25

http://www.hadleighcastings.com/uploads ... Detail.pdf

In practice a few overheating events in a 40 or 50 years life will lead to the head going to soft.Hot spots in the head around the exhaust can lead to it going locally soft in those areas so you need to check the complete head.

cheers
Rohan

Post by: **nmauduit** » Mon Dec 07, 2015 4:46 pm

thank you for the informations, Rohan. Would it make sense to heat treat again a head gone soft, or does that mean that elements from the original composition have migrated or recombined somehow? To avoid deformations from the heat variations, do you think bolting reference profiles (e.g. thick U shaped jigs) on both sides may help contain deformations during tempering, a bit like one would do when recharging?

Post by: **rgh0** » Mon Dec 07, 2015 7:37 pm

Yes in theory its possible to repeat the heat treatment to restore the hardness. In practice with a fully machined head the challenge is keeping it straight through the process as you observed. The cost would also be significant as all the seats and guides would need removing before treating and replacing after.

cheers
Rohan

Post by: **alan.barker** » Tue Dec 08, 2015 8:23 am

quote " I think I will take it to a Twin Cam expert for advice before going any further"
If you take it to Miles choose your words carefully and be sure to say it was not you that did the damage or he will shoot you at dawn and there will be a lot of bad language :mrgreen:

Alan

Post by: **el-saturn** » Tue Dec 08, 2015 9:53 am

......the easiest or visible proof is the indentation "marks" coming from the cylinder head bolts - the pictures show unfortunately exactly THAT plus the tappet sleeves started to turn due to the expansion of the aluminum!! heat "treating" a 50 year old head seems, to me, more a theoretical solution than anything else! i'm sure this is the case for a new head. cheers sandy

Post by: **Phil Standing** » Tue Sep 27, 2022 11:58 am

I don't have an Elan, but I do have a Lotus Cortina MkII using a standard C cam engine. I have been looking at the cam follower sleeve issues that have been raised and thought I might contribute this.
I have just had a complete break up of no. 3 inlet sleeve no part of which remains in situ. The shrapnel has gone all over that area of the head and although I have collected a lot, much more remains somewhere else. On hearing the noise, I stopped the car within about half a mile where it was safe to do so, so it did not go too far in this condition.
The cam follower appears to be umarked and undamaged. The sleeve bore in the head shows some marking and its' dimensions remain to be checked. In researching this problem I notice that Burtonpower can supply sleeves that are 20thou oversize, so this may have happened before, although I think it's a fairly rare problem.
Rather galling really as it has only done about 6,000miles since complete restoration and a lot of engine work. Just about the only things not replaced in the head were the sleeves. I am using Burtonpwer steel cam followers which I noticed are slightly shorter than the standard ones, presumably to accomodate high lift cams. I wonder if there is a compatibility problem here. Engine is otherwise standard.
Does anyone know of similar incidents and has any root cause been proven?
Thanks in advance.
Phil.

Cam Sleeve Damage

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