Monday, November 23, 2015

Throttle hole dimension question

Malcolm from Great Britain had sent me an email question about the 2-Jet throttle plan pages included in the V-Twin plans:

Q: On sheet 27 left side view there are 2 holes .100. from top and .570 from top and .265 from right hand edge.
I can't work this as to size, depth, threaded etc.  Can you help me with this?

A: Hi Malcolm.  Page 27, looking at the "Left Side View", I'll call the top hole #1, and the bottom hole #2. These are the two holes you inquired about .

For hole#1, the dimension reference is shown to the left of the "Top View": Drill .070 thru and tap 2-56.  Looks like you drill until you "T" into the larger .140 hole at a 90 degree angle.

For hole#2, the dimension reference is shown to the left of the "Front View": Drill .043 dia into fuel inlet, then drill .070 dia x .200 deep and tap 2-56.

This may sound childish, but try cutting out the Top View, Left Side, Front View, and Right Side, then tape them together to form a basic 3-D model, then I think it will mentally come together much clearer.

Hope this helps...

Monday, May 11, 2015

V-Twin - Construction Comments by Ernie from south Florida

I started building the Howell V-Twin four months ago, although I have a long way to go, I would like to share some thoughts and ideas I picked up along the way. Disclosure: I am a self-taught machinist.

There are dozens of small parts on the Twin. None of which are difficult to make, with the exception of one, the gear case. It’s not for the faint at heart. Precision is a must. If you’re going to make the Twin, make the gear case. After you complete the case and cover, go on with the rest of the Twin. It’s downhill from there. Don’t get discouraged. it took me four tries to finally get the case right.  Pay particular attention to the depth of the gear pockets. Their depths are each measured from the top surface of the case, not the bottom of the 2.250 dia. x .270 deep cut out. The dimensions can be confusing so read the construction notes first. Note: The holes are first drilled on the “O” ring side, then turned over to bore the pockets.

Several gears will be needed; fortunately, you won’t have to make them. All, including the tail shaft and oil pump gears, can be purchased very inexpensively on eBay; however, they will require some simple modifications. The Howell drawings specify 14 ½ degree pressure angle. The PA of the gears I purchased was not specified, but they seem to work perfectly so far.

Before drilling the holes in the gear case, test drill the holes in a flat plate. Put the gears in place on the plate to verify the dimensions to assure smooth rotation. You may have to make minor adjustments to achieve minimal backlash. 

To make life easier I used a 1” ID DOM Steel Round Tube for a cylinder liner (available on line). The tube required modification of the cylinder as designed but it resulted in a perfectly round, and non-tapered inside diameter. No lapping is needed as the inside is perfectly polished. In addition, I’m going to try to use Viton "O" rings instead of cast iron rings. More on that latter.

I intend to add more as I proceeded, so stay tuned. And please, feel free to email me [] with any questions.


A minor point concerning the oil pump and that's the gear offset from the center. There is no indication on how that gear is held in place. Just press a .125 dia. x .25 post into the center and place the gear over it. The gear will rotate around the post.

LOCKTITE 640 is specified in several places in the construction notes. DO NOT substitute another product. This stuff is incredibly strong up to 400 degrees. A small tube, although not cheap, will last a long time.

V-Twin – Pistons & Rings

On virtually every engine I built in the past, I had problems with compression. However, that problem is no more since I started to use DOM tubing as the cylinder liner. For the V-Twin, I am using 1” inside diameter DOM tube (from On Line Metals). As close as I can measure, the ID is spot on, 1.000" with no taper. The inside wall is polished smooth as glass.   Following is how I make the piston, cylinder and rings:
- Make the aluminum cylinder body first but with a 1.190” bore.
- Start with a 2” length of 1” DOM and turn the OD to 1.188” for a light press into the cylinder body, and then cut it off to length. Press it into the aluminum body.
- Make the piston blank by turning a 4” long piece of 1” diameter cast iron (which is always oversize) just enough so it is a tight sliding fit into your aluminum cylinder body. 
- Polish the piston to achieve a sliding fit into the cylinder. 
- Bore an .910” diameter hole ¾” deep in one end of the piston blank, actually the ID of the rings.
- Part off six rings from the piston blank (I usually cut off a few extra) each about .045” wide. 
- Now, cut the ring grooves as specified on the drawing and complete the two pistons.
- Using fixture A, sand (150 grit) the rings just enough to fit the width of the piston grooves.
- Using a diagonal cutter cut the rings forming the ring gap.
- Using a very fine file, lightly file the two ends of the gap. 
- Place the ring on fixture B.
- With a torch, heat the ring opposite the gap until it turns red for about 20 seconds.
- Remove the ring (let it cool). The gap will remain open but will  close with a little pressure then spring open when pressure is removed. 
- Now it’s a matter of putting the rings on the piston and inserting the piston/ring assembly into the cylinder. That may take a little effort.

You’re done! It took me about five hours. Hope this helps. Note: Email me for a sketch of fixture A&B.


I found machining the V-Twin carbonator quite challenging and one of the more difficult parts to make next to the gear case. So much that it took me three tries to get it right. In my opinion, the original drawing is just too confusing and that lead to the errors in machining the part. As a result I redrew the carbonator body using conventional drawing and dimensioning practices. If you would like the drawing send me an SASE and I will gladly send it to you, but ONLY if you purchased the V-Twin drawing set from Howell. Email me ---

Tuesday, March 3, 2015

V2 fan hub assembly explained

Here's an e-mail thread I thought would be a good topic to share with others:


Hi Allen,

Last time I emailed you, I was 80% complete in a few months, I’m getting a little closer now.

I’m working on the fan, Sheet #35. Because there are no assembly drawings on many of the subassemblies, it makes things interesting, like a puzzle. The fan hub takes a .156 x .312 flanged support bearing for the Fan Shaft. But where does the other bearing go. (a shaft needs two support bearings). I assume it goes in the Fan Belt pulley. But in you kit of bearings there is no bearing that size.

As always thank for your help.


From South Florida: Weather report for today - 81 degrees


Hello Ernie,

Hey - no fair bragging about your weather!

After some study and speaking as an amateur, here's what it looks like to me:

1. Insert a .156 ID x .312 OD x .125 flanged bearing, flanged side out, all the way onto the Fan Shaft.
2. Insert the Fan Hub into onto the Fan Shaft, narrow end attached to the bearing from step 1.
3. Insert the second .156 ID x .312 x .125 flanged bearing on the Fan Shaft, flanged side out.
4. Insert the Fan Belt Pulley onto the narrow end of the Fan Hub.
5. Attach the Fan Mounting Bracket on the remaining exposed end of the Fan Shaft.

See if that makes sense to you.




That cleared it up.  In summary there is a ball bearing inserted on each end of the Fan Hub. But, why is there a .500 dia x .190 dp cut out in the Fan Belt pulley. I think it would have made more sense to put the other ball bearing in the Fan Belt Pulley. 

One more thing, the gears. Cutting gears is expensive due to the cost of the gear cutters and a rotary table. The gears can be purchased from SDP or other gear houses, expensive. However, I purchased then on eBay for about $3.00/gear. Only slight modification is needed. If you would like more info just ask me. You may want to pass it off to others.

I certainly appreciate the help, thank you again.



Yeah, I wondered about that deep cut on the Fan Belt Pully.  I can only guess that Dad did not think it needed all of that bearing surface contact, and also makes it easier to disassemble should the need arise.  He knew he would have to disassemble the engine after he built it to draw up the plans (contrary to typical product development, Dad built his engines first, then developed the plans after!)

Send some of that sunshine and warm air up here.  We could use it!