Making cast iron valve guides

[Shox Dr]

View attachment 108576

First one made. Size worked out ok but the biggest issue I have is getting the hole parallel to the OD. What is seen to be the correct way/professional way to get the hole drilled straight. I'm new to this machining stuff. It wandered off by maybe 15 thou?

By the way, Meehanite machines nicely.

Are you using a four jaw to hold it, after turning down the OD, or leaving it in a 3jaw and parting off

 

[cocker]

Or drill/ream 1st
Turn between centres or on a mandrel

 

[rtbcomp]

It's normal to ream once they've been fitted to compensate for any squishing when they're drifted/pressed into place.

 

[cardiffrob]

I only have a 3-jaw chuck on this thing (Hobbymat MD65). I had a 2-inch piece in the jaws, countersunk the end, drilled the undersize bore, machined the outer dimensions and then parted it off. There is 20 thou difference between the thickness of the wall at the top of the guide, suggesting 10 thou wander. Is it likely to be a rubbish drill bit, a tailstock out of alignment, wander due to the material, etc etc? Would I get a better result if I drilled the initial hole from each end to the halfway position? Would MT drill bits be a better bet? Should I need to tap driil bits straight so they are perfectly centred on the countersink? Soooooo many questions....sorry.
Hole is currently 6.5mm against a final figure of 7mm + clearance.

 

[Seadog]

I would machine the diameters and then centre drill. Through drill allowing 10 to 15 thou for reaming. Once reamed to finished size part off. That way the accuracy of chuck is irrelevant. As for a morse taper drill, it won't make a great deal of difference. Drills inherently wander and drill oversize, especially if the grind is not perfect.

 

[8ob]

The chances of the valve ever landing on the seat correctly are pretty slim if you try an ream this without a guide . I have a bronze guide insert tool thats for rescuing worn guides, it centres the aligning tool off of the original seat which puts the finished guide in the right place. At the very least make a tapered plug with a hole in it that fits and guides the shank of the reamer ( like the one in the first photo ) or you will end up stoning the valve and seat ( because paste will never do it) which will recess it ( lower compression and screwed valve geometry ).

Bob

 

[cardiffrob]

Wellllll...I tried the Mk2 version by drilling the 7mm hole with a good cobalt 6.9mm drill and reamed it out in the lathe without removing it. After that, I ran a 7mm silver steel rod down the hole and into the chuck. Lubricating the rod meant I could centre the cast iron on the rod to ensure that the OD of the guide was concentric with the ID. Seems to have worked out alright. I have almost zero clearance so I'll need to hone it somehow. The valve seat inserts are all corroded so I think I'll insert these guides and get the seats recut professionally.

The 'precision' 7mm rod is actually 6.96mm along the full length. After all this messing about I have come to the conclusion that it would be better to go for a 6mm hole and to run another drill and reamer out to 7mm AFTER the guide has been inserted, utilising some sort of wedge under the head to get the angle and some sort of cone-shaped guidance device (as 8ob put in the 1st pic above) to get the hole right.

Thanks, everyone.

 

[graffian]

The few times I have made guides I stick them on a valve seat pilot held in the lathe and take final light cuts to size them.