Flathead valve job question

V

Vonn

Junior Member
Will the machine shop need the valve guides in or out to do the seats in the block on an 8BA flathead block? Asking for a friend.

I posted this question over on the HAMB a few days ago and got various reply's. The obvious suggestion was to "ask the machine shop", which we did and the answer was, "I use a pilot".

Others suggested that the only way to get the proper job was with the guides in place. While that would seem logical, you couldn't put the valve assembly in as a complete assembly. Or could you remove the guides after grinding, then assemble the valve and spring and put the valves/guide back in.

I know there are some really great engine builders here, and I'd love to hear their opinion on this. Thanks!
 
Repeat--"Ask the machine shop" They are the ones doing the job.
The last couple I had done the machine shop had any adapters that are required.
 
51 MERC-CT said:
Repeat--"Ask the machine shop" They are the ones doing the job.
The last couple I had done the machine shop had any adapters that are required.
Click to expand...

Thanks 51 MERC, as I said in my original post, we did exactly that, but I was hoping to get an opinion from some of the old time builders that post here from time to time concerning the merits of using a pilot versus using the valve guide as a pilot. thanks
 
Some machine shops have a pilot to match the equipment they use, such as Sioux ,Black &Decker ,Van dorn etc. it never hurts to supply a new guide when you take the block to the machine shop , I use a pilot that came with my seat tools , I found out sometimes the pilots get bent and don't allow the stones to center with the seats , I have used a guide which I added Teflon ring to help keep it stable in the guide bore, the pilot is tapered to keep it in place while grinding. we all have our on ways to achieve this task. So ask the machinist .
Fordestes
 
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I used a Pilot for awhile that registered in the lifter bore. I found out lather that these are not necessarily in alignment, and switched to a pilot that fit the guide bore. The seat indicator shows only a coupla thu run out.
 
Ol' Ron said:
I used a Pilot for awhile that registered in the lifter bore. I found out lather that these are not necessarily in alignment, and switched to a pilot that fit the guide bore. The seat indicator shows only a coupla thu run out.
Click to expand...

Thanks Ron, was hoping you would chime in on this.
 
I have pilots which register in the block guide bore and the lifter bore. I have found this system will sometimes put the seat in the wrong location. I have found the better system is to use tight fitting guides for the pilot.
 
Given the amount of typical "slop" that I see with out-of-the-box guides, I do not use them for seat work. My machine shop made a custom mandrel that picks up the guide bore and has a very slight taper to it - such that it will be a tight fit. The seats are then done in a vertical milling machine - with the block in a set of main bearing "saddles". Using the mill with it's 'digital readout' - also gives us the ability to set consistent seat depths. In many cases I've had oversized seats installed (for 1.72" valves), so everything is new - having the mill setup with multi-angle cutters sure helps in setting the initial top-seat depth, associated angles, etc..

JWL brought up that "tight fitting guides" can be used - but they don't usually come that way. You can put a very slight knurl on the guide-to-block surface . . . to tighten them up a bit (I do this). BUT, some say that knurling guides can really reduce the heat transfer between the valve assembly and the block (exhaust gets hot!). So, I definitely don't want a big knurl. Some guys use a form of lock-tite to "cement" the guides in so to speak - them assemble things the hard way (as you no longer can easily drop the valve, guide, spring, retainer assemblies in from above - as the guide is 'glued' into the block. Lots of ways to skin the top-end flathead cat . . . and as many opinions as you know whats. LOL

I will continue with the custom mandrel approach - followed by a slight "hand lapping with very fine compound" and die-chem - using the actual valve guide for the lapping operation. The lapping is primarily done so I can validate the sealing surface, location and seat width (just another check before final assembly). Usually I then rotate the engine and pour a bit of solvent into each port - to see that all valves are sealing and none are "weeping fluid".


Enough of my babble . . . starting to bore myself!

B&S
 
Another option to tighten up the guides is to have them plated - typically it is a copper plate that is used to increase the diameter of the OD.

Obviously this means you either hone/ream the inside guide bore back out, or install bronze liners, etc.. This requires time, fitment, etc - but it is a very good way to achieve a tight fit and still have great heat transfer.

Some guys love bronze liners and seals, some just use the stock stuff. I tend to run high-end stainless 'Pro-Flow' type valves with chrome stems, so I don't have a rust issue in the guide bores.
 
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