Replacing valve guides

[wishbone]

I'm going to be renewing valves, guides and seals on my 1098 at the weekend and having never done one of these before i'm wondering how easy the guides are to drift out and replace. Does anyone have any advise or method that might save me time or damage?

[Dominic]

Hi wishbone

I have just had a problem with two valves, needing replacement along with their guides. I attempted to drift them out, but the ends of the guides started splitting, so I'm afraid I decided to take the cylinder head to my local engineers. Chickened out in other words! It seems they won't be charging much luckily.
Good luck
Dom

[wishbone]

yes that was my worry. The manual says drift out and drift in (simple) but I dont trust manuals, i'm usually a few hours behind schedule with bad temper and bleeding knuckles! Ther must be an easy way to do these though?

[bmcecosse]

It is easy enough to do - BUT you MUST have a drift designed for the job. It needs a centre part to fit snuggly inside the guide - same diameter as valve stem - and then step up to a diameter just a few thousandths smaller then the o/d of the guide. Without this - it's hopeless. Get the 'local engineers' to make you this - and then you are all set. Always drift them in the same dirrection - ie into the combustion chamber. And just do one at a time - using a straight edge across the others as your guide to how far to knock the new one in.

[wishbone]

Thanks for that, its just the advice i needed.
My mate with the lathe is away for a couple of weeks though, but I reckon I could make something from an old cut down valve and valve guide if i grind it down a little and seat a little of the valve taper in the seat. i'll give it a try anyway!

[Dominic]

you MUST have a drift designed for the job.

Hmmm that's why my method didn't work.......

[bmcecosse]

Maybe someone on here is (semi-)retired and has a lathe - and could knock these up and sell them to folks on here!!

[Dominic]

I can supply the necessary elbow grease required at only 1/6d a tin

[alex_holden]

If you get stuck and can wait until next week, I could lend you the one I made. Just pay the postage and send it back when you can.

[Innovator]

After fitting guides you should recut the seats.

[bmcecosse]

Not often necessary - if the guides are well made they should still give a true centre to the seat. They will need a good grinding in though.

[les]

There is a measurement for the distance between the guide tops and the deck of the cylinder head where the spring sits, it is 19/32 inch, you can in fact 'build' this feature into the insertion tool, if you make one, so as you can't knock the guides in further. Rather than hit or miss it's better to re-cut the seats lightly after fitting, you know you've done all you can then.

[bmcecosse]

But v few people have seat cutting gear ! I have always managed ok with a good re-grinding - first with rough paste and then finish off with fine.

[les]

Only stating the generally accepted correct way, no doubt you have managed in the past. The re-cut seat allows you to get a narrow seating when grinding in, as opposed to a wider one that excessive grinding gives. One theory being the wider the seat the more heat transfer to the valve.

[bmcecosse]

The other theorey (more widely accepted I believe) being the wider the seat - the more transfer of heat AWAY from the valve! The valve is uncooled (except be seat contact) - the cylinder head IS cooled.

[les]

God, what are you like after a drink!!