Valve seat material for LPG.

Road-race engines and ancillaries - general discussion
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4v6
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Joined: March 20th, 2007, 1:20 pm
Location: Midlands UK (A)
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Valve seat material for LPG.

Post by 4v6 »

Hello Guy I hope you're well, I wonder if you can help with a question related to valve seat materials suitable for LPG use in a turbocharged engine?

Basically I have been tasked with the job of exhaust seat insert removal and replacement on an Audi 20 valve head, its a job I have undertaken before and so the process is not entirely new to me.
This has become necessary due to the exhaust valves being replaced with client supplied inconel items as the stock two piece items tend to suffer from the heads coming off them at high-ish mileages.
The client wants to use these inconel items, however I found out a while back that the seat inserts in the head are 27mm diameter at their outer periphery whereas the stock valves are 28mm, in other words they overhang the seat insert with the seat placement being somewhat inboard towards the stem.
The two photos show the lack of a contact area when lapped together and their poor locations.
Inconel exhaust valve, overhangs the seat insert and contact area located too far inboard.
Inconel exhaust valve, overhangs the seat insert and contact area located too far inboard.
P1090618.jpg (173.63 KiB) Viewed 4516 times
Seat insert is smaller on O/D than the valve, contact area located too far outboard and too thin.
Seat insert is smaller on O/D than the valve, contact area located too far outboard and too thin.
P1090617.jpg (170.75 KiB) Viewed 4516 times

The new inconel items have a 2.0mm wide contact area and are also 28mm diameter but its contact area is located at the outboard edge of the valve meaning any seat is going to be far too thin, indeed I've heard of people just dropping these items in and using them, I can only imagine theyre going to run into seat life problems before too long, so with that in mind I have to put in larger inserts of 28.50mm to accomodate the valve correctly.

The question is what insert material would you recommend for the application?
Sintered, copper alloy, stellite?

Any help you can offer as ever gratefully appreciated.

Tony.
Tony Warren. GC #96.
Guy Croft
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Re: Valve seat material for LPG.

Post by Guy Croft »

KS do a high expansion sintered alloy especially for LPG. I recommend it.

They have an online catalogue but I suggest you call my friends Stanwoods at Bawtry on 01302 719842 and discuss sizes.

The head should be bored out to suit the insert not the other way round. The inserts care precision ground on OD. There is a huge range of sizes. The fit wants to be 0.002" - 0.004" and the inserts must be chilled in liquid nitrogen and the head heated up to 120 - 150 deg C and the insert dropped in with a piloting mandrel that centers in the guide. The bore in the head should have a radius - seat has a chamfer. This is precision stuff for an expert.

After fitment the seat needs recutting. Much depends on the state of the valve guides.


Get them to do it if you like, they do work for me so I can speak without reservation for their capability. They are so good I rarely do inserts myself these days.


GC
Guy Croft, owner
4v6
Posts: 205
Joined: March 20th, 2007, 1:20 pm
Location: Midlands UK (A)
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Re: Valve seat material for LPG.

Post by 4v6 »

Thank you for your advice Guy its very much appreciated.
I have used KS (motorservice gmbh) for the last one I did and have now found the product line you referred to.
I've also sent an email to them to confirm sizes and so on.

I've seen the online catalogue with recommendations for fitting etc and interference fits which I've had a good look at.
Also yes, you're right its precision stuff indeed, the last insert I replaced I used my Mira seat cutter to produce an accurate counterbore to get the correct interference fit and I made a mandrel as you suggested to get it all square, all very in depth and somewhat nervewracking.
The seat manufacturer suggests cold pressing these inserts due to their inherent springiness, using a force of approx 700kgs to fit them, which is what I used last time and I did see 700kgs upon fitting, it went in perfectly, still it it does not stop me from worrying.
The guides are brand new items from TRW so all counterboring and seat ops will be generated from those new items.

Thanks again for your help with this Guy, Tony.
Tony Warren. GC #96.
Guy Croft
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Joined: June 18th, 2006, 9:31 am
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Re: Valve seat material for LPG.

Post by Guy Croft »

thanks Tony for your kind acknowlegement.

Don't cold-press!!!


G
Guy Croft, owner
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