I wanted to mock up the new top end to double check the squish. I knew Al needed to deck the top of the cylinder but I wanted to bolt it up and measure it on the actual motor. I quickly found that you can get the head off but you can't pull the barrel off as it sits.
I have a motorcycle jack so I put it under the bike and removed the rear shock bolt. With the bike raised and the motor tilted down, the cylinder slides right off. I've been tripping over the jack for years now.
Everything looked in pretty decent shape. I did find that the base gasket had a crack in it.
Here are some side by side shots of the stock top-end versus the reworked Pinasco from Al. You can really see the difference in the boost port.
The Pinasco cylinder for the 200 has the transfers in the cylinder and not cut into the cases. Just like a stocker.
In order to make up for the reduced transfer area in the cases, alot of work is done to the piston to compensate. You can see that Al really does alot of work here. Pretty nice shape for a used kit.
The head is recut and the combustion chamber opened up a bit. The stock Pinasco head has a pretty low volume and needs to be modified to work properly.
Here's a shot of the piston at BDC so you can see the ports.
OK. Yeah this is a bit ridiculous. With my old RS125, I used to lay one piece of solder across the top of the piston to measure the clearance. Here, the gap was so big, I had to practically braid a rope to make it work. What I usually do is place a piece of solder on both sides of the wristpin. That way it won't tend to rock the piston in the bore. I stick it to the top of the piston with heavy grease. Put the head on and rotate the motor a couple times. Then you can pull the head off and retrieve the crushed solder.
In this case the gap is huge. With so much solder, its probably not very accurate. I was getting between 3.4mm and 3.5mm of gap. Eek. that won't work. We were shooting for around 1.2mm.
The plan was to take material off the top of the cylinder to compensate for the negative deck height. The goal is to set the piston for zero deck height and have the squish cut into the head. In order to get a good measurement, you need to make sure the cylinder is securely held down. I did this by slipping some sockets over two of the studs and then bolting the cylinder down. By doing this I could use the depth measurement on my calipers. I measured in 4 places around the perimeter of the cylinder and determined the piston was a little over 1.7mm below deck.
To be honest, I will probably bolt it all back together and check one more time. I'll put the top ring on this time and double check. The Pinasco uses an L-shaped top ring. Without the ring on, there is a fair gap between the top edge of the piston and the cylinder wall. I want to make sure the caliper fell correctly on the outer edge of the piston and wasn't getting in the gap. Better safe than sorry you hacked the top off your cylinder.
Sure enough I bolted it all back together and measured again. This time I put the top ring on and switched to my older dial calipers. They have a fatter depth probe. This time I was getting around 55 thousands (1.4mm). I think we'll go with these numbers to be on the safe side. Worst case I can always lap the head down a bit.
I did grab a set of feelers gauges as a sanity check to see where I was. Between 1.5mm and 1.7mm seemed right. When Al puts the cylinder back in the lathe, he is going to cut an o-ring groove in the top.
One option that I want to talk to him about is leaving the cylinder as is and cutting the head so it goes into the bore of the cylinder. This will allow me to go to a stroker later and not throw all the timing numbers way off. If I cut the cylinder, I would need a packing plate later. If we can do the head this way, he will need to add dowel pins to the head to center it as there will only be about 0.3mm protruding into the cylinder.
We decided against this as the edge of the chamber will be small and pretty short. the odds of damaging the lip during assembly is pretty high.
As an FYI, the super high end Seel race cylinders used on the RS125 had the cylinder almost 2-3mm taller than normal and had the combustion chamber recessed way into the top of the cylinder. They did this for detonation reasons. On the RS125's, deto would erode the top edge of the cylinder and perimeter of the head. Copper rings were cut into the top of the cylinder and the perimeter of the head as it didn't get eroded as easily.
I went ahead and took a couple measurements off the head to see where it was at.
The nice part about the Pinasco is that it is close to a bolt on. Mine has had some pretty extensive port work so the boost was opened up a bit. I went ahead and cut the base gasket to match the cylinder and laid it on the cases to see how far off it was. Hmm... pretty big difference. I decided to match the boost port up in the case.
I marked the top surface of the case with a black Sharpie and traced the outline with an Xacto blade.
I jammed the case opening with paper towels and covered the rod up. Everything had a pretty good coating of oil on it so any stray fragments weren't going to go far. I used a cutter on a Dremel with a flex shaft. I cut so it would throw must of the fragments out. To be honest it went real quick and easy. I pulled the towels out and everything looked real clean. If you take your time and make sure everything is plugged up good you should be able to keep the chips out of the case.
So with measurements in hand, the head and barrel head back to Fresno for the final adjustments. I just need to sync with Al on the final plan on how we want to reduce the squish.
Last edited by chuckactor on Sun, 04 Sep 2011 23:28:29 +0000; edited 1 time