1920 Harley Model F

[wowswitch]

Hi John,
here is a page from my book... the plates are for a sidecar motor, just take them out. as for piston i was told to use HD VL pistons, they work and much cheaper, i got mine from

https://aaok.com/index.php/motor-flathead-ul-1/vl-and-ulh-3-7-16-piston-sets/020c-o-3-7-16-vl-80-ulh-piston-sets-020-inch-oversize.html

sidecar.jpg
good luck Ken

[TechNoir]

Hi John,
here is a page from my book... the plates are for a sidecar motor, just take them out. as for piston i was told to use HD VL pistons, they work and much cheaper, i got mine from

https://aaok.com/index.php/motor-flathead-ul-1/vl-and-ulh-3-7-16-piston-sets/020c-o-3-7-16-vl-80-ulh-piston-sets-020-inch-oversize.html

good luck Ken

Thanks Ken. My bike had a sidecar originally so it fits with the compression plates.

My engine is a "J" so its 61 cu in so the VL pistons are too big unfortunately. I have had a few suggestions on what pistons to get for a J though.

John

[TechNoir]

Re: 1920 "F" Project

I am off next week to see a guy about a re-bore. Obviously a re-bore means new pistons and new pistons will be aluminium as opposed to the originals that are cast iron.

So my question is what is the recommendation regarding balancing the crank assembly when changing from cast iron to aluminium pistons?

Thanks,

John

[T. Cotten]

I am off next week to see a guy about a re-bore. Obviously a re-bore means new pistons and new pistons will be aluminium as opposed to the originals that are cast iron.

So my question is what is the recommendation regarding balancing the crank assembly when changing from cast iron to aluminium pistons?

Thanks,

John

John!

I would first attempt to back-calculate your original balance factor.
Just put the assembly on knife-edges, and then add weight to the rod tops until it comes to balance.
Then after weighing the piston assemblies and rod tops, the math is easy:

Piston assemblies plus rod tops equals your total reciprocating weight.
Added weight to achieve balance, plus rod tops is your 'trial' weight.
'Trial' weight divided by the total weight gives the existing factor.

Then, when you know the weight of the fresh piston assemblies, you can decide the best way to add or remove weight to achieve the same factor.

....Cotten

[TechNoir]

Thanks Cotten. I guess that the crank will need rebalancing so that will be something else to do.

John

[exeric]

There is some very good information here.

http://www.antiquemotorcycle.org/bbo...gine-balancing

[T. Cotten]

John!

You won't know for certain until you measure it.

Please also be aware that you probably would not find a factor worshipped by modern cradle-frame enthusiasts, as you have a single down tube design.
The frame design figures heavily in factor choice: http://virtualindian.org/Flywheeltheory3.htm
My best guess is that you would find it in the lower forties, similar to VLs.

Balancing doesn't always mean carving on the flywheels.
You may be able to make up the difference in pistons with thick-walled wrist pins, or "slugging" them. Please weigh all piston assemblies before splitting the cases!

....Cotten

[TechNoir]

Re: 1920 "F" Project

Eric, thanks for the link. That is interesting reading, I need to read it a couple more times and digest it but like you say it is good information.

Cotten, thanks for the information and link, again good information that I need to read and digest. One question though, why do I need to weight the piston assemblies before splitting the cases? Why would it not be OK to weigh them after splitting the cases?

John

[T. Cotten]

John!

If the piston assemblies can be matched, what is the sense in splitting the cases?
(Unless you fear the crank is a mess, too...)

Just trying to help,

....Cotten

[TechNoir]

Re: 1920 "F" Project

John!

If the piston assemblies can be matched, what is the sense in splitting the cases?
(Unless you fear the crank is a mess, too...)

Just trying to help,

....Cotten

Doh! Its obvious now that you say it. Thanks for the help

John

[TechNoir]

Hello folks, well its time for me to post a small update on my 20F and hopeful more updates to come in the near future.

If you remember I found that the bores were in bad condition. The first port of call was to find someone who could be reliably trusted to bore out these blind cylinders. I spoke to Steve Slocombe who kindly put me in touch with the guy that he uses, the only downside was that he was 250 miles away.

I also spoke to someone more local who came recommended so I went to him.

The first thing he noticed was that my cylinders had been relined previously. This must have been done some time prior to 1936 which is the last time the bike was on the road. I left the cylinders with him and to cut a long story short it turned out that the existing liners have cleaned up nicely. As well as the scores and pitting the bores were also oval. No wonder it ran like a smoke machine. I have been told though that the previous lining job was actually very good. There are still some marks at the very bottom of the bores but they are below the rings so it is not a concern.

After a debate and lots of thought about new pistons, I decided to go with new cast iron pistons so I spoke to another specialist also reasonably local to me who could cast them for me. I picked the pistons up just before Christmas. Here is a picture of the new piston castings, one old piston and the core box and pattern.




Here is a close up of one old piston next to a new casting. Somewhere inside the one of the left is something that looks like the one on the right.




I would have quite liked to have machined the pistons myself but 2 things put me off. One, I would have been really annoyed if I had made a mistake. Two, my milling machine isn’t functional at the moment so I don’t actually have the equipment available to do them. Therefore I got someone to machine them for me. I have used a more modern style plain cast iron rings which have been kept high to make sure that they avoid any of the remaining few marks at the bottom of the bore.

I picked the pistons and cylinders up this morning (14th April 17)


Once I knew that the pistons were done I knew that the next job was balance hence my post over in the Engine section.


I deliberately hadn’t pulled the bottom end apart until the pistons were done so that the disassembly will still be reasonably fresh in my mind when I go to re-assemble it. One evening this week I reduced it from one lump into lots of bits.







That brings things up to date. Whilst that is happening I need to find someone to machine the cylinders to accept new exhaust valve guides because the new valves are at best a rattle fit in the old integral guides.

I do have a couple of other jobs to do which I had delayed until I had the engine work in hand so hopefully everything will come together in time to get some miles on the bike in the not too distant future.

Watch this space.

John

[exeric]

You certainly have been busy, and productive, John; and your timing looks like it will work out quite well, with Summer just around the corner. I am so impressed by your thoroughness, and desire to make your '20 run well. I am looking forward to hearing your impression of it's road manners. Are there some good places to ride in your vicinity?

[Jim]

These "Build Threads" always amaze me on what you guys can do! Even though I don't have an "F" Model, I've been "watching" this build.

[TechNoir]

Thanks for the comments guys.

I am looking forward to hearing your impression of it's road manners. Are there some good places to ride in your vicinity?

I am keen to get to know how it rides too Eric.

Without publishing my exact address on here I live in a village just to the west of the City of York. If you dont know, York is a very historic city and is very popular with tourists.

I live in a very rural area and the roads outside my house have on average probably 1 car every 15 to 20 minutes. Also I am also close to the North York Moors and also the Yorkshire Dales which are also very picturesque.

If I ever get it on the road I will see if I can borrow my Nieces GoPro and put up a video.

John

[exeric]

I would love to see a GoPro of your region, John. When you say Moors, I think of those fantastic Hammer horror films of the '60s with Christopher Lee, and Peter Cushing. With those guys around, you would want a motorcycle that could get up and go at a moments notice