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Seasoned Chat Slut
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Discussion Starter · #1 · (Edited)
Hi all,

I have recently purchased some valves for replacing mine as they are quite dimpled and as I have the engine out think it would be a good thing to do.

Now I stupidly bought the wrong sized inlet valves, 35mm (standard I think?) and now I have (one of) the old valves off I measured it to be 39mm.

Now rather than spending £80 on 4 new 39mm valves, which is very expensive for me. Can I just use the 35mm valves with some grinding paste and not change anything else? Should I get my wallet out and stop being such a cheap skate? (or get 4x40mm for £60?)

It's a 1641 TP twin cam (I have swapped Weber 44s for Weber 39s.)

Cheers

Jeester
 

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Highly Respected Member
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13,500 Posts
If you can fit the smaller inlet valves, and lap them in so you get a seating area around 2mm wide successfully then they'll do the job.

You can't get away with smaller exhaust valves though, they need some meat around the edge to cope with the extra heat.

Check for guide slop while you're there, especially the exhaust guides. Sloppy exhaust guides can trash your entire engine, including the case.

Dave.
 

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Seasoned Chat Slut
Joined
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1,276 Posts
Discussion Starter · #3 ·
If you can fit the smaller inlet valves, and lap them in so you get a seating area around 2mm wide successfully then they'll do the job.

You can't get away with smaller exhaust valves though, they need some meat around the edge to cope with the extra heat.

Check for guide slop while you're there, especially the exhaust guides. Sloppy exhaust guides can trash your entire engine, including the case.

Dave.
Hi Dave,

Thanks for the reply. I have tried to wiggle them around in the guides and there is a miniscule amount of movement (like I can feel it but not really see it if you know what I mean).

Is this acceptable or will they need replacing too?
 

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Highly Respected Member
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From memory, maximum wear limit in the guides is 0.75 mm measured at the head of the valve, but check your manual to be sure. Exhaust guides wear out faster than inlet guides.

If they're beyond the limit, they can be replaced, or you can have liners fitted.

Dave.
 
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