Uneven exhaust valve tip wear

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guzzit3
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Uneven exhaust valve tip wear

Post by guzzit3 »

I have a 1984 Excel with the LC type engine, and I checked the valve clearances over the weekend.

7 out of 8 of the exhaust valves were fine, all around 0.25mm. However 1 valve, the 3rd one from the timing belt is almost double the clearance: 0.45mm

So I took the cam shaft carriers off the head so I could measure the shims, and I found some odd shim and valve tip wear on the valve with the 0.45mm clearance, it looks like a big lump. Here's a pic:

Image

The shim has a matching wear pattern also:

Image

All the other valve tips and shims are flat, they have a mirror like finish. All exhaust shims are a pretty similar thickness, including the one which isn't flat.

So I was wondering what the best way to going about fixing this would be? I was thinking I should order the correct size shim and somehow sand the valve tip smooth again? I may even be able to do this without having to remove the head.

Or I could replace the valve which involves removing the head, which is something I'd rather avoid. I think it's running the original head gasket, and the replacement head is different and needs uprated studs AFAIK.

Has anyone else seen this sort of wear and is it anything to worry about? Has anyone attempted to sand down valve tips without removing the head and if so, any top tips? Finally, how can I see if I have updated studs? I've heard that they are dimpled but I've never seen what this is supposed to look like.

AndyC
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Re: Uneven exhaust valve tip wear

Post by AndyC »

I wouldn't sand the end of the valve, as you'll probably just introduce new unevenness which will then in turn wear away the shim further. I wonder whether those valve stems have been ground by a previous owner/ mechanic and you are seeing the result of uneven grinding. In my mind you should remove the valves, have them ground professionally so that they are completely perpendicular and smooth if the engineer agrees it is possible (they may already be ground so far that the metal is not hard enough now), then re-shim. I guess you may not be keen to do it but you cannot really measure valve clearances properly with that indentation & pip, so all I can say is it's probably best to do it once and do it well rather than have to come back to it in 12m time when it's got even worse.

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DavidOliver
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Re: Uneven exhaust valve tip wear

Post by DavidOliver »

Many engines with overhead direct cams have the cam lobes set slightly off-centre to the cam follower to induce a rotation which avoids a wear pattern on the cam follower surface. From the photographs you appear to have had a dry surface between shim and valve, perhaps even some leftover valve grind paste, and the rotating cam follower has ground down the shim/stem.
It also appears that the cam follower has had interference with the valve spring retainer following the wear on the shim AND the valve.
I do not know if the Lotus valve tips are hardened, if so you will have worn through this.

In my opinion you cannot resurface the valve tip in-situ, it will never be flat and cleaning afterwards is ni-on impossible.

To lift the head is a DIY job and as dismantling, cleaning, etc. is labour intensive more reason for DIY.
A good time to consider a decoke and valve seat clean-up.
On reassembly apply a little engine oil to the shim/valve tip surface.
You will need to reassemble dry to measure for the necessary new shims so do not seal with gasket goo, (there is no gasket between head and cam carrier).
For the new head gasket ask around to get the right thickness, but it is not essential on the LC engine.

Dave the cog.

guzzit3
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Re: Uneven exhaust valve tip wear

Post by guzzit3 »

Thanks for your useful info and advice, I'd rather to a proper fix instead of having to worry about it wearing again in the future, so I'm going to replace the valve and shim.

I'll do some research into what head gasket is required, and order it along with the valve, shim and a few other bits.

Pete Boole
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Re: Uneven exhaust valve tip wear

Post by Pete Boole »

You can use the "new style" head gasket with your existing studs - just use the original torque settings. The uprated studs simply allow higher torque settings to be used. You do lose a tiny bit of compression due to the extra thickness of the gasket, but I doubt you'd notice. Gary Kemp sells uprated studs/washers/nuts if you want to upgrade - they are what I'll be using.

Pete

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