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Old 06-18-2017, 04:24 PM   #24
Track Rider

ygolohcysp's Avatar
Join Date: Sep 2008
Location: Whitehall, PA
Posts: 954
eBay ID: theovergrowngnome


Okay, time to update once again. I've suffered another engine failure, this time not as significant. Another issue that was hindering my engine longevity was the cam. Apparently, the powroll cam was produced by a company called web, which is known by a few people to produce cams for these engines that are too aggressive, and don't have a ramp on the back side to slow the closing of the valves. I noticed it myself this time by wear finally showing up on the cam lobes, but being suspiciously absent on the closing side of the lobes. It was the cam that came in the bike. This time, it broke the top of the valve off, so the valve dropped, got bent, broke the valve guide, and aside from little scarring, left the head and piston in tact.

I purchased a smaller lift cam from a known good company, but as always, decided to play a bit with the rebuild. I found an intake valve from a brand, Psychic, that was black oxide coated for reduced friction and already undercut with the head shape changed for better flow. That meant I didn't have to try doing that part myself, which I had planned.

In the time since my last update, I upgraded mills as well. The one I got is old and used, but it's a full size Bridgeport with a 9"x42" table. All I can say is wow, that mill runs nice. I haven't touched the small one since I got the full size. Anyway, the mill comes with with the head. There was small scaring around the edge of the head that provides the squish, so I decided to try my hand at milling the head down. I assembled the motor with clay on the piston, rotated through a couple cycles, and measured. I then milled the head and remeasured. I got the exhaust valve to piston clearance to .070". Perfect.

I also did more port work on the head, smoothing out the ridges where the valve seats stuck into the port. You know, the opposite end of the hardened material from where the valves sit. I also removed a fair bit more material from the intake side. Having tried it out since then, all I can say is WOW. The compression is definitely noticeable. I was already starting with a high compression piston. Now, the kick back on the kick starter is impressive when I get it wrong. In switching to a smaller lift cam, I managed to either hold the same power, or even increase it throughout the entire range. The porting work on the exhaust side also served to up the usable rpm limit quite a bit. Using GPS, I've clocked it at 63mph, and I ran out of road while the engine was still climbing. All in all, not bad for a 150 with a 5 speed.

Last edited by ygolohcysp; 10-30-2017 at 08:43 PM..
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