Help on valve chest drilling

[Alan Worland 1Participant @alanworland1]

I have started the valve chest and cover for my S/T No 4 engine, and mounted the valve chest in a chuck and have centre drilled and put a pilot hole through the gland end. The hole needs to continue through the open part of the valve chest and into the other side of the casting opening, ie across an open space of about 1 1/2in !

How can I reliably continue this hole through to the inside face opposite?

The gland hole is finished reamed 3/16, and the one on the far side is 1/8.

Any advice?

[Alan Worland 1Participant @alanworland1]

[JasonBModerator @jasonb]

You could buy a long series centre drill, they can be had upto 6″ long.

J&L sell the long ones

 

Or make your own, drill out a bit of 3/16 rod to 1/8″ and loctite a BS 1 ctr drill into the hole.

 

Jason

[mgjParticipant @mgj]

One addition I like, especially on an iron casting is to put in a centre spot first – these things can skid a tad on a bumpy casting.Shouldn’t but it can.

 

A bit of 3/16 silver steel. Turn to a point , drop it down the gland hole and tap lightly – no need to harden for a one off. Then as Jason says.

 

if it doens’t come out right, not all is lost. Oil the gland hole, and then drill out to 3/16. Make a bronze plug .001 oversize, (at which point you discover what size your 3/16 drill is actually cutting) and press in with a c clamp. Then start again and declare that you wanted to have the tail guide bushed.

 

Jason – thanks for that about J&L. I will invest in one – a long centre. The drills I just loctite a jobbers drill into  rod, as you suggest.

Edited By mgj on 08/02/2011 19:59:11

[JasonBModerator @jasonb]

Its best to look through the “virtual catalogue” rather than try searching teh site, page 99 is what you want.

 

I have been going over to using spotting drills more and more lately as they don’t skid about as much as a ctr drill (thanks bogs).

 

Needless to say whatever method you use file the inside of the chest flat to stop the drill being pushed off line if its not already machined internally.

 

J

[John OlsenParticipant @johnolsen79199]

i’ve sucessfully done a few Stuart engines as per the suggestions above, eg file the inside of the chest so the surface is flat, then use a home made centre punch. A normal drill is usually long enough and will start fine on the centre punch mark.

 

regards

John

[Alan Worland 1Participant @alanworland1]

Thanks chaps, I wasn’t planning on machining the inside face s of the valve chest but I can understand doing the face I am trying to start a centre on as it has a typicaly cast surface (bumpy) and wants to affect the starting of a drill.

I think I like the idea of a long centre punch, as the gland hole is not up to size yet I can see how it all goes!

I did even consider (for a short time!) coming in from the other end and filling the end with JB Weld

Don’t know what come over me!

[Author]

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