THE THINGS YOU LEARN

Recently I have been messing about positioning the big bit of the Overland to get a feel for what the frame will be.  In the process the gear box and clutch basket and the drive cog on the engine needed to be lined up for the first look.

All went smoothly until I got to the chain cog on the engine main drive.  I had a splined stub and a nut but no obvious way to secure the cog.  Well at least obvious to this novice but aspiring garage monkey.

I couldn’t even figure out what type of fixing I should be looking for in the spares.  So I grabbed a photo and put out a query to the JAP engine experts who read a JAP engine facebook group.  Sure enough I got several quick replies regarding how the splined stub, nut, cog and the missing fixing, a circlip, should work.

Well I found the packet of circlips in the spares and fitted one up.  Now here is the explanation of this arrangement for the JAP.

Speedway bike frames are designed with a bit of flex to them.  Something about the torque, no gear box and turning left.  Well that’s what the experts said.  Anyway so as a result of the frame flex the main chain cog splined stub was design such that the main cog could float a bit on the splines as the frame flexed and keep a straight chain line with the jack shaft.  The purpose of the circlip is so you can quick change main cogs rather than having to deal with dismounting the rear wheel to change the hub sprocket.

It sure makes sense to me once it’s all explained.  Never would have thought of that but I’m not a speedway person; just barely a motorcycle guy.

FIRST LOOK AT THE OVERLAND FRAME

This is just a start of the frame build.  This entire project has been about using what is available first and then filling in the gaps as I need things.  As a result of also imposing the one-off criteria the frame jig will be used once.  So it has sort of a DIY look to it.

The bench was an old TV stand from a friend that I put wheels on.   The main beam is folded steel left over from a Land Rover project and the upright was snagged at the recyclers.

So here are some numbers.  The base is 3 inches in height.  The rear wheel is a stock 18 inch Honda DID rim.  The upright is 2 inches wide.  The height from the bench to the rim gives me a starting tire sidewall of 3.  So to get a feel of the placement in relation to the spine tube the distance from the back edge of the spine is about 5 5/8 inches, which should give me plenty of room for a tire side wall of up to 4 ½ inches.  Of course I have to do some more checking on available tires before I commit to those dimensions. 

The gear box and engine are going to be close coupled with alloy plates with the gear box adjustment for chain tension to the engine main shaft on the top.  The bottom of the box will pivot on a mount point near the base of the spine tube.  Well I hope.  If things work out the general gear box engine ground clearance should be a bit over 3 inches.

What I’m trying to get is a fairly short and stiff rear triangle.  I’m not flat tracking this so stiff in the rear hind quarters should build in less flex in a light weight frame.  At the front end will be a head tube rack of from 20 to 28 degrees.  From the head tube will be a down tube to a bracket which will carry the front engine plate.  So the engine and the gear box bolted together will become a stressed member of the frame. 

With the girder fork at the front the trail should be in the range of 31/2 to 4 inches with the 19 inch front rim and a tire side wall of from 3 to 4 1/2 inches.

We will see.  There is much work, fiddling, blocking, measuring and such before tubes start getting cut and welded along with cutting alloy plate and the list goes on.

Tool Time!

While my brain processes all the possible frame style options and choices it seemed reasonable to think of special tools for the garage.  So here are some additions to the tool box for Kiotee Garage.

First up since I sort of got side tracked by an inquiry regarding a possible spare magneto I realize that when it comes time to put some fire in the cylinder of the JAP it would be nice to know if the timing for the points in the mag would be to spec.  So I scored, with a Christmas gift card, an Aircraft Tools single cylinder magneto test light and buzz box.  In addition I also scored a nice 1 inch micrometer while pawn shop crawling with my son.

And as long as I was thinking of things for the engine I realized I needed a purpose built valve spring compressor to fit the JAP head.   With the help of my son I cut an 8 inch c-clamp in half and added a two inch bar.  Then ground and shaped one end to take a valve stem.  I also added two bits of oak tanned leather on both the valve stem side and the face so the valve won’t get scuffed or scared from installation.  Seems to work just fine.  Need to do a bit more clean up finishing but for now it will do.