Hobbsy

My Feedback: (102)

A good friend of mine passed an older Davis Diesel conversion head on to me, it has no designation on it that I can find. The bore is .87" and the depth of the part that extends into the cylinder is .22" without the gasket in place. It is set up for six 6x32 bolts. I could not find an engine in my collection that it will fit. Thanks for any help anyone can come up with.

earlwb

Hummm, A bore of .87" sounds like it is a Fox .50 engine bore. They use six 6x32 screws to hold the head on too.
Of course the last Irvine engine I tinkered around with used 6x32 screws on the head as well. So maybe a Irvine .53 like engine would fit too.
I'll check tonight and see if I have a Fox .50 cylinder out that I can measure or not.

Hobbsy

My Feedback: (102)

Thanks Earl, I think I can rule out the Fox, I tried the head on a Fox .46 sleeve I have as an extra and its a very loose fit. I'm going to go and re-measure, I may have 10 thumbed the measurement. A K&B 45 has a .85" bore and may be the winner. On my micrometer if turn the screw the least bit extra the mics body will flex a tiny bit. I'll be bach.

Hobbsy

My Feedback: (102)

Earl, i used a .5" bit shank and calibrated my mic. and it now reads .85", so I'm leaning toward it being for a K&B .45 Sportster. Now, if only I had a .45 Sportster. I have a well worn Sportster .65 but no joy.

AMB

Dave most folks buy an engine then the Davis head to fit it quite a different approach, well if we go by weight maybe you are 10% or so there good luck, good guess?? you may be right, time for Mr Davis to confirm martin

Hobbsy

My Feedback: (102)

Hey Martin, that ain't the first time for that, I have a head for an OS .61sf but so far no engine. Somehow I just can't part with a perfectly good Diesel head.

AMB

Dave DISASTER just pulled my Fox 50 off the shelf went to pull the diesel head and it has 2 stripped holes in the block noticed the screws were loose (2) they look small 4/40 3/48 ?? may have send it back to Fox and I am careful when I put them in this is a first for me martin

Hobbsy

My Feedback: (102)

That is bad, they are 4-40s and can't handle much torque, 4 oz in is about it. If you have a 3-48 tap you could go there and see what happens, you can't lose much now.

AMB

Will give it shot with the 3/48 and the 4/40s stock are short if that fails will send it back to fox maybe they can reblock it martin
If we went 6/32 the head would need the original holes milled out I really do not want to do that I want the head stock and the engine too martin

Hobbsy

My Feedback: (102)

I gotter figured out, I decided to check the specs for the K&B ball bearing 40 and discovered it has a .84" bore converting to 21.336mm, looky here. The .45s bore of .85" converts to 21.59.

AMB

Dave May have a save, just ran my 4/40 tap down the hole which is very long picked up as much good thread area as stripped out put in a long 4/40 cap good bite, bottomed out just needs to be shortened martin

.87 and .85 bore well no cigar yet

Hobbsy

My Feedback: (102)

Good job, keep us posted.

Here is picture of the K&B .40 ringed engine there is also an ABC version. What a lousy picture, I'll get another one.

AMB

Dave will hit the LHS for the 4/40 screw and take engine with, might get lucky that way no cut down on the long one so perfect threads martin

ddd

Could be a OS .45 FSR or SF. American engines that have 6 bolt heads have the bolts inline but Japanese straddle the center line.

pjwright

Old thread... but Bob typically hand engraved the engine the head was intended for on the underside. I'm looking at one right now that says "ST7590", meaning a Supertigre G75 - G90. No one think to look? :-/

1200SportsterRider

There is or was no writing on that one. I long since sold it.