Changing valve guides

[maxfax]

This car is supposed to get me out of the "he drives a beater" class without getting a car that I really hate haha,

HAHAHA..  Nice cushy cars don't have to be boring, but I gotta say I've had the most fun with beaters...

[rabbitman]

Well, I went and ordered a whole set of valves and guides from air cooled engines plus.

[rabbitman]

Well I found out I have valve and seat refacing setup, I'll need to get the proper size stones though since the ones I have for aircraft engines and therefore HUGE compared to what I need.

[Mark(The Miser)UK]

Well I found out I have valve and seat refacing setup, I'll need to get the proper size stones though since the ones I have for aircraft engines and therefor HUGE compared to what I need.

Clearly lots of money floating around  Alaska
Why do you need to do anything other than lapping a new valve in with coarse and fine paste, and a childs arrow with a rubber suction cup on the end?

[rabbitman]

I talked to the guy at air cooled engines plus and he said valve grinding compound went out with the model T and all lapping does is remove 100,000 miles from the new valves.

So the best method is perfect valves (which I assume these will be) and perfect seats and theoretically they'll seal perfect. The only problem is I have to make the seats perfect on my first try.........

[sdwarf36]

The reason the guides wear is there are very short in design. Gas or diesel-its just how the head is.
 I have every machine shop tool availbile at work-and to r+r the guides in my head-I used a proper sized guide driver + hammer.  Thats all. They aren't in there THAT tight. I do throw them in the freezer for a while before installing them. (I may have also run the head thru the parts washer to warm it up some--but were talking only 120* or so.)
 For heads that are known to have really tight guide fits, I'll drill the guide out 1/2way down to larger size-and then hammer+ drift it out-so its pushing from the middle. (it saves the end of the guide mushing over+ screwing up the hole.)
 Odds are good that you will have to ream the guides out slightly-but even if its only .001 or .002 you need, you still gotta do it. And there is nearly zero chance that the the valve will seat same as the old guides-so you WILL have to cut the seats.
 I'm suprised the machine shop is scared to work on your head. Short of having pre cups where the spark plugs would be, this head is the same as a gasser-and have been around for almost 40 years. This is run of the mill stuff-nothing fancy at all.
 If you want to box it + ship it across country, we can do anything you need to do on it. We aint scared. 

[rabbitman]

I would've liked to have someone else do it but after shipping it around and then paying labor cost will add up way to fast.......and after re-remembering that we have seat grinding stuff here I'm kinda excited to do it .

This http://www.cylinderheadsupply.com/sisthdvasegr.html is really close to what we have except for the selection of wheels and pilots are probably different.......and ours is way older.

[Mark(The Miser)UK]

I talked to the guy at air cooled engines plus and he said valve grinding compound went out with the model T and all lapping does is remove 100,000 miles from the new valves.

So the best method is perfect valves (which I assume these will be) and perfect seats and theoretically they'll seal perfect. The only problem is I have to make the seats perfect on my first try.........

Interesting how modern technicians would think that grinding in with paste would take more flesh off than machining...

 Apart from removing the hollows from pitted valves, due to valves burning due to not shutting correctly
[I've never seen this on these engines]; using paste, is merely to ensure, and reveal that a brand new pre cut valve [aren't they all these days] seals all round, by the finest of seal edges

[Remember a valve should never be machined to the same angle as the seat].
The pencil thin seal area ensures a perfect seal, but if you are looking at  a 3mm width seal, [as revealed by the 'matting' effect of the fine paste], then the technician has spent far too long lapping;  perhaps erroneously thinking wider the better.

Minimal fine paste lapping is essential to ensure that machining has created a seal for yesteryear, today or tomorrow, PERIOD.
Any technician, engineer, or amateur who thinks otherwise, is  regrettably, out of the loop of maintenance, and merely a part swapper.

If there is a lathe operator who can take off less flesh from a valve head than fine lapping does then I'm impressed. If you think about it a lathe can only remove a layer from a plane, not a point

[rabbitman]

So if a guy has new valves and installs new guides then the seats must be ground to make it all line up again. If after doing that the valves seal good then there's no point in lapping them at all, I think accuracy today is good enough that it everything should seal fine.

The other thing is lapping removes material from the valve and seat, grinding and polishing the seat only takes material from the seat without putting a ring in the new valve.


I'll find out, if I do all this and can't get a good seal I'll lap them a little bit.

[Mark(The Miser)UK]

So if a guy has new valves and installs new guides then the seats must be ground to make it all line up again. If after doing that the valves seal good then there's no point in lapping them at all, I think accuracy today is good enough that it everything should seal fine.

I agree it should all fit snug, but then again the head itself is still old and may be twisted around the guides slightly, and the seats could be out slightly due to years of being thumped at high temp.

A totally harmless check for sealing, is to use some metalworkers blue on each valve and seat, and rotate once and check for continuous line.
Also with valvesprings in, but not cam, drop some kerosine onto valve heads...

The other thing is lapping removes material from the valve and seat,
Remember it's purpose is to create a matched pair, just as the advocates here on lapping the old injector body onto a new nozzle helps [if not messed up] the body to seal. grinding and polishing the seat only takes material from the seat without putting a ring in the new valve.


I'll find out, if I do all this and can't get a good seal I'll lap them a little bit.

[rabbitman]

Yeah the guy did say to put that blue stuff on there and shut 'em and see were it's clean.

[sdwarf36]

If you dont have any machinist die-magic marker works just fine. And you are better off with just slapping the valve against the seat-or rotating the valve slightly-it will show if it is seating all the way around. If you turn it a full lap, the high spot (if there is one) will make the mark everwhere-you won't be able to tell if you are getting good contact all the way around.

[R.O.R-2.0]

yeah i think the right way to do it is to remove the cups, surface the head then skim the same amount off the top of the cups or the top of their hole in the head, then reassemble the pre cups are supposed to stick out a small amount to account for heat expansion

supposed to fly-cut the bores after you surface the head with the cups out..

[Mark(The Miser)UK]

If you dont have any machinist die-magic marker works just fine. And you are better off with just slapping the valve against the seat-or rotating the valve slightly-it will show if it is seating all the way around. If you turn it a full lap, the high spot (if there is one) will make the mark everwhere-you won't be able to tell if you are getting good contact all the way around.

Ah good pont, you got me there ...                                                      Except you put marker on both faces

[rabbitman]

So I'm installing the new guides, for some reason the guide that was worn is also oversize so I'm talking with air cooled engines plus to see what we can do about that.

In the meantime I installed the rest and am in the process of reaming 'em to fit the valves.

The bentley says "with the valve keeper end flush with the guide and using a dial indicator on the edge of the valve head, the maximum slop permissible is .051". (not word for word )

When setting new guides and valves what should it be using the bentley method?

The guy at air cooled engines plus said that if I can feel any slop with my fingers then it's good, but I'm not sure if that's at full lift, bentley method or just off the seat.