Questions on New Guide Installation
 

Hi All

In order to obtain the correct interference fit of 0.002" to 0.003" on a 3.6 litre, one can either hand ream the bore to the guide's OD or turn the guides in a lathe to match the bore. Is this correct? Never having used a hand reamer, can one obtain as precise a fit as I believe one could obtain turning the guides on a lathe? I would image turning the guides as the prefered method as no material is lost from the head.

All responses appreciated
Bill

I always order 2nd oversize and turn them down to spec. Its good to turn them between centers on a mandrel, this will cleanup any taper in the guide center also, they are not that straight as purchased.

Craig

Do I understand you correctly in that new guides have a taper? I would have thought they would have been perfectly straight in order to have complete contact along their length in the bore which I assume will also be straight. If this is the first time the guides are being replaced would all the bores have the same dimensions or should I expect variations in the diameter of the bores provided none of the aluminum is pulled out during removal of the old guides?

Thanks in advance
Bill

The guide or bore is really not tapered in the way I guess I said it but I find the center bores are not always bored straight, some can be slightly angled and when you go to cut the seat you will end up taking more of the seat to correct for this condition. I am only talking a thou but by the time it extends to the seat it can be as much as 5 or 6 thou off. I just like them as straight as possible so only a small amount is taken off the seat, this will also give you more rebuilds until you have to replace the seats.

I have done hundreds of heads and have always found the bores in the heads to be very consistent. I never go over .002 interference fit.

Craig

Now I understand, in that the center bore isn't always perfectly parrallel to the outside of the guide and by putting the the guide between centers on a lathe you're trueing it up relative to the center of the bore.

Thanks for taking the time to clarify this
Bill

Craig,

I've turned down guides but found them to cut kinda gummy. Seems I can make a .002" cut but then go back over with the same tool position and cut some more. Makes it hard to get an exact .002 fit. Do you have a special technique to overcome this situation?

Tom

You should really not get any deflection cutting bronze, Are the cross feeds loose maybe? What lathe do you have? Are you grinding your own tooling or using inserts? Make sure your bit is at or just slightly below the center line.

Craig,

I have a Grizzly G4003G gunsmith lathe and am using inserts. Maybe the wrong type of insert? Or maybe just need to lower the insert a smig, like you suggested. I am using a live center so it has to be something simple.

I'll lower the cutter a bit on my next guide run.

Thanks Craig.

Tom...

I just got a set of heads in to do so shot a vid of sizing the guides, may be kind of dumb but I like pictures!


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Craig...not dumb at all....great video.

How about another one on case resizing??

Craig

Great attention to detail!

Thanks for sharing.
Bill

Great video Craig

Post installation, do you hone or ream the guide bore ?? - I've not seen the honing tooling or process on holes this small (8 or 9mm)

John

John: I use both, ream then hone, I have two hones, a small ball and brush hone, I actually like the brush better it does not hone as quick. You really have to ream them to cut the guide straight on all sides after its installed because it will crush a bit. To install them I just use my air chisel and made a tool with a depth gauge on it. They go right in but make sure to use some lube or it will never go!

http://i30.photobucket.com/albums/c3...1/100_8488.jpg
http://i30.photobucket.com/albums/c3...1/100_8486.jpg
http://i30.photobucket.com/albums/c3...1/100_8487.jpg

Greatly appreciate the detail and tips Craig

Thanks
John

Craig,

Nice vid and pics. Thanks very much.

Tom...

Good idea with the air chisel. Does the fsm call for baking the heads in order to install the guides?

Only for seats.

cgarr,

What's a good grit and size hone for the valves? i've seen 9, 9.5, and 10 mm and all have various grits.

I like the 240 Grit, Ideal for Precision, Final Fitting of Valves to Guides

Thanks cgarr.

Do you think the 9mm hone would be too small to effectively hone the guide? Would the 9.5mm work better? I also read that people use lapping compound during the honing process. Do you think it's necessary?