A Long Span Between Races

It wasn’t cold when we started the season at Talladega, early in February. But it sometimes seems so long ago. However, with all that time to prep the next generation GP350 race bike, it definitely has not been long enough.

Keith has been helping me get my footings firmly planted on motor rebuilding. Of all the things I have done to a motorcycle, the bottom end has remained a mystery. We both have learned a lot during this episode of vintage motor work. Keith learned about a tiny little plastic ball inserted into the lower casing that, lucky for him, just never fell out.

We also spent a good bit of time trying to diagnose what happened to one of the motors that “my hero, Mr. Charly Perithian of Parabellum Ltd“. donated to my racing cause. It was a great example of a freshly rebuilt motor that still had zero sludge in the centrifugal spinner/filter on a motor that didn’t last the weekend. With much trepidation, Keith and I moved forward diagnosing the salvageable parts.

I had to cut the rocker housing in half to pull the cam out in hopes of salvaging that baby. Mr. Dean Middleton recommended muriatic acid to clean off the aluminum from the steel cam. The top end really took a hit and that was part of the puzzle we had to work with. The points housing, which also doubles as a cam journal broke in half while extracting it. The tach housing, the other cam journal did work out with a lot of persuasion, but was still useless for future motors.

There was no sign of damage to the head nor to the upper motor mount and oil deflector plate. So, all the damage was contained inside the rocker housing level.

We looked at the oil pump and it showed no signs of an “out of normal” state. The ports which pass the oil showed no issue. This is where we discovered the little plastic ball. Our best guess of why the ball is there, is to make up for one too many drilling points in the original design. But, based on my experience, that ball does its job just fine.

As we had all but given up on finding the problem, I brought in the side covers from the blown motor. I pointed out to Keith how one of the three oil access plate cover screws refused to leave the casing. Then when I showed him how I had damaged the access plate, he looked on the inside. Then he reached for the one we were going to use instead of the damaged one and he found it.

Missing part that causes the cam to lock up and the motor to stop running

The shiny washer like plate that encircles the protruding cylinder on the right, is the part that is missing on the left. That is why the oil never made it to the top end. It simply circulated around in the bottom end.

The access plate also acts as the channel for the porting of oil through the centrifugal spinner. The bad one had a circlip that neither of us had seen before. That is because the circlip is supposed to hold on an important part, that on this plate was missing! When we looked at the manual and followed the path that oil takes to be filtered and then sent to the top end of the motor, we noticed what this part does.

Without this “metal oil guide”, which is a spring-loaded deflector plate, to send oil to the top end of the motor, the cam is starved and will lock up. We were quite relieved to find the problem versus proceeding with having transported the problem to the new motor. The hardest part about this is figuring out how that could have come off, if the circlip was still in place???

So now, we have the upper and lower crankcases properly torqued together and ready to continue. We did have some fun making the clutch part go back together. In this process, we have come to the conclusion that although this may be the most interchangeable motor ever made in the almost half million quantity, it is still best to keep certain parts that have had time spent together, staying together.

Next stage of the motor is the gaskets and engine side cases. This will be followed by the cylinders and my new 1.0 over piston set from Sirius Consolidated Inc. that will take the 325cc motor to the maximum 335cc allowed for this indexed motorcycle. Before the top end is installed, I must install the new valves that Sirius also sells at the amazing price of only $79.

I know this is my race blog, but when the assembly of this next generation race bike is complete, I’ll have a list of the items used to modernize it. And, you might be surprised to find just how many items that are supported on this 44-year-old bike. But, don’t be surprised by who supports it!

As always, thank you Mr. Martin Mattes for sponsoring my vintage racing efforts. I can’t brag about you and Sirius Consolidated enough.


About videojackster

A freedom loving libertarian who really enjoys experiencing that freedom on a motorcycle, on the race track, as often as possible.
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