Lotus Elan

Inlet valve - replace or reuse?

PostPost by: nigelrbfurness » Wed May 17, 2017 7:20 pm

Just stripping a big-valve head ready for skimming and I see that no. 4 inlet valve has some slight pitting (after cleaning off the carbon) on the inside face (ie combustion chamber face, not valve seat). I presume this occurred as a result of the head gasket failure and is related to water entering the combustion chamber. The seat and sealing face of the valve are both fine and show no signs of damage. A compression test prior to stripping was good - the head gasket leak into the cooling system only became apparent when the engine was hot and running at high rpm - so the seat to valve seal was obviously ok. All the other valves are fine too. As I have no spare 1.562" inlet valves in stock, I'm wondering if its ok to reuse it. Normally I would just replace it with a new one but this rebuild has both time and budget constraints. What, if any, are the likely dangers from re-using this valve?

Your opinions are valued and I thank you in advance.

Nigel F.
1970 S4SE/1760cc big valve/SA-AX block, L2s, 45DCOEs, 1978 Jensen GT, 1962 AH Sprite, Alfa-Romeo 159, 1966 Bristol Bus, 1947 AEC Regal bus.
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PostPost by: Chancer » Wed May 17, 2017 9:30 pm

Sounds completely normal to me based on back in the day experience.

Enthusiasts are a lot more knowledgable these days thanks to modern communication and forums like this so someone may well have information to the contrary.
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PostPost by: nigelrbfurness » Wed May 17, 2017 9:40 pm

I suppose it will work perfectly well as long as it seals to the seat. I was concerned that the pitting might indicate that the hardened surface of the valve was disintegrating. I'm worried about premature failure - ie the head falling off the stem! Looking at the other valves, the heads were all smooth once the carbon had been cleaned off.
1970 S4SE/1760cc big valve/SA-AX block, L2s, 45DCOEs, 1978 Jensen GT, 1962 AH Sprite, Alfa-Romeo 159, 1966 Bristol Bus, 1947 AEC Regal bus.
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PostPost by: MarkDa » Wed May 17, 2017 10:21 pm

You're obviously concerned and if your fears are realised you will definitely feel penny wise pound foolish.
Let's face it a new valve is less than ?20, surely worth it for peace of mind?
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PostPost by: nigelrbfurness » Thu May 18, 2017 8:16 am

That's a fair point. A new valve it is, then.
1970 S4SE/1760cc big valve/SA-AX block, L2s, 45DCOEs, 1978 Jensen GT, 1962 AH Sprite, Alfa-Romeo 159, 1966 Bristol Bus, 1947 AEC Regal bus.
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PostPost by: 2cams70 » Thu May 18, 2017 9:27 am

Be sure to properly grind or recut the seat to match the new valve though! Otherwise there's a strong possibility it will leak and eventually burn due to blowby of hot combustion gas (been there done that). Take a picture of the suspect valve too. Let's have a look
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PostPost by: john.p.clegg » Thu May 18, 2017 9:36 am

Nigel
"As I have no spare 1.562" inlet valves in stock", did you mean 1.625?

John :wink:

May have a couple
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PostPost by: nigelrbfurness » Thu May 18, 2017 1:09 pm

John, this is what I ordered: http://www.burtonpower.com/inlet-valve- ... fl818.html

I guess they could have got the dimension wrong in the catalogue entry, but I'm assuming that a Sprint inlet valve is a Sprint inlet valve... Wikipedia quote 1.565" for "big valve" twin cams. My workshop manual is in the garage and its raining so can't be bothered to go and look what that says :D

Seriously, the valves in my allegedly big valve head are slightly bigger than the standard ones but not enormously so by comparison, maybe 15thou? I think 1.625" is bigger still but I'm not an expert.

In replying to the other advice, yes, thanks, I'm aware I will need to lap in the valve to the seat. I've just done all the exhaust valves as they were a bit manky, though the seats are not bad enough to require re-cutting. The inlet valve seats look very good and as the compression was fine beforehand I'm inclined not to redo them apart from the new one. I always put the same valves back in the same position in the head, under some probably mis-guided assumption that the guides and stems will have bedded in together... and the tappet clearances will remain the same!
1970 S4SE/1760cc big valve/SA-AX block, L2s, 45DCOEs, 1978 Jensen GT, 1962 AH Sprite, Alfa-Romeo 159, 1966 Bristol Bus, 1947 AEC Regal bus.
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PostPost by: JJDraper » Thu May 18, 2017 5:19 pm

Never had a problem re-using all the valves, inlet and exhaust, after replacing head gaskets and giving the head a general clean and face. Valves & guides last replaced nearly 100k miles ago. Three head gasket replacements since then with the head and valves cleaned and checked each time by a trusted machine shop. Last time the valve seats were re-faced as well. Valves, seats & guides were supplied and fitted by QED in 2003.

Unless you are racing, I'd reuse them.

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PostPost by: AHM » Fri May 19, 2017 7:05 am

Given your criteria, if it is within spec. I would reuse it.

For me that would be better than having one odd one.
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PostPost by: reb53 » Sat May 20, 2017 6:54 am

Getting a little off topic but...
when I replaced all mine years ago, I was sitting at my work bench and idly tapping one old exhaust valve against another and watching the carbon chip off.
Then one of the heads did as well, 2 tiny little bits of shiny metal were all that was holding it on......... :shock:

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PostPost by: rgh0 » Sat May 20, 2017 9:08 am

If reusing valves I would always crack test them looking for a crack where the head joins the stem. The can crack their due to being bent during assembly or small misalignment that flex the head every engine cycle.

I have had a used valve head drop into an engine so I am a little paranoid now with used valves. Reconstructing the whole head dome in one cylinder :shock: is not cheap

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PostPost by: billwill » Sat May 20, 2017 1:24 pm

A relic that I keep to remind me that once upon a time I didn't understand that Twin-Cam valves and pistons occupy the same space at different times. :shock:

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PostPost by: JJDraper » Sat May 20, 2017 4:49 pm

They can crack there due to being bent during assembly or small misalignment that flex the head every engine cycle.
Surely this would apply to new valves? I don't rev the engine much beyond 6.5k, and even then only for very short periods. Racing is different...

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PostPost by: rgh0 » Sun May 21, 2017 12:08 am

JJDraper wrote:
They can crack there due to being bent during assembly or small misalignment that flex the head every engine cycle.
Surely this would apply to new valves? I don't rev the engine much beyond 6.5k, and even then only for very short periods. Racing is different...

Jeremy


Yes misalignment can also happen with a new valve if the guide and seat are not aligned properly or if you have excessive wear in the guide or seat. The flexing of the valve head on the stem to the point that a crack appears is most likely on a used valved in a worn or poorly machined head. Even if everything is concentric and square to the right tolerances and fits in the new assembly, a used valve may have a crack already from its previous life that will lead to a premature failure.

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