valve guides

Post Fri Jun 30, 2006 12:40 am

hi guys,
have just started working on the cylinder head for my m42. I'm looking at doing something with the restriction posed by the valve guides to the inlet ports, but I'm not sure whether I can. The valve guide is 4.5cm long, and the bit that sticks out into the inlet port is about 0.7mm. I've considered shaving about 0.5mm off the bottom of the guides, opinions? 4cm is still quite long, iirc the valve is about 105mm in length total.
here's some pics:

Post Fri Jun 30, 2006 8:13 am

Couldn't smooth them into a kind of tear-drop shape could ya? (absolutely no idea what that might gain you though!)

Is it an optical illusion, or are the inlet valve throats smaller than the exhaust?!

Post Fri Jun 30, 2006 9:25 am

Conventional tuning practice is to "sharpen" them like a pencil.

Post Fri Jun 30, 2006 11:27 am

Brianmoooore wrote:Conventional tuning practice is to "sharpen" them like a pencil.

yeah, i think i might pay somewhere to taper them down, and mb just shave a mm or 2 off the bottom. will be a pain, as i they'll need to be removed i reckon...

turbo-brown, nah the inlet port throat is bigger mate!

thanks for the replies guys!

Post Fri Jun 30, 2006 11:44 am

how far back is it safe to take them?
getting work done on a head at the moment and have been told due to the length of the guides they can be taken right back - i have been googling around but cant seem to find any info on safe tolerances.
any ideas?

Post Fri Jun 30, 2006 3:09 pm

liam012 wrote:how far back is it safe to take them?
getting work done on a head at the moment and have been told due to the length of the guides they can be taken right back - i have been googling around but cant seem to find any info on safe tolerances.
any ideas?

is this on an M42? if not on what head and do you have the measurements etc and how much would be taken off etc.
cheers
tim

Post Fri Jun 30, 2006 4:22 pm

This is my M30 inlet valve guides/port, which was done by.........

http://www.cylinderheadshop.co.uk/

Post Fri Jun 30, 2006 6:19 pm

My M30 ports have been done too, with the guides all made flush with the roof of the port. I've had same thing done on a few other engines and never had a problem.

It is possible the guide can wear a little quicker due to sideways forces of the valve being controlled slightly less (maybe not at all with hydraulic lifters) but even using old (but not excessively worn) guides has never been a problem for me, I suspect it would take many years and many thousands of miles to notice anything at all.

Go for it, lop 'em off!
[img][img]http://i59.photobucket.com/albums/g307/ ... EGUIDE.jpg[/img][/img]

Post Sat Jul 01, 2006 11:16 am

Have taken valve guides back to the roof of the port on many engines now and saw no problems, and they were race engines, the valve guides were in good condition to start with.

Post Sat Jul 01, 2006 1:34 pm

cool, thanks guys this is really useful. Looks like they've got to go!
Cheers
tim

Post Sun Jul 02, 2006 9:47 am

Just make sure that the remaining part of the valve guides are in good condition

Post Wed Jul 26, 2006 1:32 pm

Hey tim sorry didnt get back to you on pm's regarding this, but i would find out if there is enough clearence between the top of the guide (with seal attched) and the max lift of the valve with the top retainer. IF there is i would get someone to move the guide up into the cylinder head and then just cut the rest of it off!

Also have a look into using a smaller veavle stem valve as you will save on weight and air flow restrictions (even though the stem doesnt really restric the air flow too much)

Here is a pic of a Motorsport S14 head.

HTH

Andrew