Lotus Elan

Removal and rebuilding of a Twincam

PostPost by: rgh0 » Thu May 14, 2020 9:07 am

My head machinist will check both sleeve bore and alignment and integrity of the support around it as well as hardness test the removed sleeve. Talking to a few engine builders locally and overseas the one opinion appears to be inadequate lubrication due to to tight a fit - but I struggle with this as once it wears a little the fit would be OK and it would stop wearing and this sleeve had worn 100 times more than expected .. or .. a faulty sleeve material in some way. . I have another head to build also that needs re-sleeving of the followers and maybe I will try brass or alloy sleeves that some people are now using rather than the standard cast iron, but it should not be necessary as hard steel followers on a cast iron sleeve should be a good wearing combination.

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Rohan
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PostPost by: 2cams70 » Thu May 14, 2020 12:32 pm

I concur with the opinion that it's most likely a lubrication problem of some sort. My bet is that it's something to do with the oil pressure feed to or through the inlet cam. The oil flows through the cam from front to back. If there was some sort of restriction at the front of the cam it could be that although there may have been enough flow at the front of the cam to keep things lubricated by the time there was leakage through successive cam bearing journals from the front of the cam to the end where the number 4 tappet is located the amount of oil was insufficient to keep things properly lubricated. Wear may not have necessarily shown up on the bearing journal there itself depending on the exact alignment of the individual cam journals - some of the 5 may have been sharing more of the valve spring load than others.
I'd also be interested to know whether the end float clearance for the connecting rod on the crankshaft journal that was damaged is still within specification. Judging by the way the bearing shell extruded out the sides of the connecting rod it could have caused damage to the crankshaft here.
It's an interesting story so far!
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PostPost by: rgh0 » Sun May 24, 2020 9:27 am

Got my parcel of parts on Friday from Tony Ingram - 2 days by DHL door to door California to Melbourne. I got a set of his new black nitrided stainless race valves which I will try in the next engine I build that I am collecting bits for in addition to the current rebuild.

IMG_8516.JPG and




Spent the day measuring valve springs to decide whether I need fit the new ones - the old ones measured up OK with no change since new in length versus load and as they have only done three years in the engine I will probably not change them.

IMG_8522.JPG and



The parts from QED are on their way and the Carrillo rods are a few weeks way still but I have plenty to keep me busy on the rest of the engine while waiting for parts and for the head and crank machine work.

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Rohan
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PostPost by: Davidb » Sun May 24, 2020 10:05 pm

Just like Christmas!

Rohan: I like the look of that valve spring pressure tester-is that a commercially available unit?

This guy has a good video-for a BMC A series pushrod engine but still interesting to watch:

youtube.com/watch?v=M0ktwq4ICYY
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PostPost by: rgh0 » Sun May 24, 2020 10:41 pm

Davidb wrote:Just like Christmas!

Rohan: I like the look of that valve spring pressure tester-is that a commercially available unit?

This guy has a good video-for a BMC A series pushrod engine but still interesting to watch:

youtube.com/watch?v=M0ktwq4ICYY



Yes - i think I got it from one of the US racing supply places, I cant remember which, it was around A$100 and its here on Amazon

https://www.amazon.com/ProForm-66835-Va ... lp_pl_dp_2

Simple 1 square inch piston with a pressure gauge that reads in PSI thus direct reading of spring load in lbs. I measure the spring compression with a vernier

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PostPost by: rgh0 » Sat May 30, 2020 4:18 am

Still collecting parts

Picked up the cylinder head today - nice new follower sleeve in No.4 inlet. Unfortunately could not get a hardness test done as the guy had to fully machine it to get it out cleanly but he said it machined like normal cast iron. He has done many twink heads and said he had never seen a sleeve wear like that before so he could not explain the wear.

IMG_8553 (1).jpg and

IMG_8552 (1).jpg and


Also got the parts I have been waiting for from QED.

IMG_8554 (1).jpg and


So just need the crank back in a couple of weeks following ist grinding and new heat treatment and I can start reassembly as hopefully I have everything needed for both this engine and for the rebuild and modification of my other spare race engine to run on 98 Unleaded rather than Avgas also thats next on my list. Then I need to decide what I am going to build after that, maybe I will actually get around to that big capacity road engine I have been promising myself for my Plus 2 for years :D
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