Plastic camshafts?

scotto-

Custom 4-Stroke Bike Builder
Jun 3, 2010
6,508
11
38
Ridin' inSane Diego, CA.
Some of these 4 strokes are using a polymer or plastic camshaft...
Are they holding up?
Seems like a weak point to me, but maybe I am wrong??
Anyone have any issues yet?
For the most part they work just fine. I have found a few on the Huasheng 49cc that had bubbles injected in the lobes and caused premature wear. The cams didn't fail as I caught the problem in time which was thousands of miles of hard riding the bike since I built it.

The gear itself showed no excessive wear and there should be no worries in their use.
 

Tony01

Well-Known Member
Nov 28, 2012
1,389
828
113
sf bay area
Yep they work fine, I think I read somewhere that they are phenolic but I could be wrong. They do make for easy hand regrinds should you want for higher lift and/or duration.
 

scotto-

Custom 4-Stroke Bike Builder
Jun 3, 2010
6,508
11
38
Ridin' inSane Diego, CA.
Come to think of it, the first HF 212cc Predator engine I bought had a plastic cam gear that was molded to the steel camshaft. It held up just fine till I dropped a higher performance .275 ground race cam in it.

Currently I am running a .307 lift race cam and I don't really see any need to go bigger with my latest set-up. It's around 25+ HP at his point, more power than needed for whatever.

Racing again a week from today...can't wait!



brnot
 

Allen_Wrench

Resident Mad Scientist
Feb 6, 2010
2,786
4
36
Indianapolis
I too have heard that the better-made plastic cams work and last just fine. But I have also heard the caveat that they work well for the engine's specs, horsepower, and torque, *as it was originally manufactured*. Just like with any engine mods you might want to do, you'll always want to look at every component attached further down the line and find out if it can handle the stresses that the modification would put on it. It'd be embarrassing for one of us to add a higher-compression head, performance exhaust, performance intake, racing carb, and 415 chain, and then at the next jack-rabbit start he rips out several of his 14-gauge spokes, or turns a corner at higher speed and the rear tire turns around and leaves him.
I'd be okay with plastic engine parts, generally, but I wouldn't modify anything until I learned more about how strong and resilient it was, and whether others had success doing so.
 
Last edited:

msrfan

Well-Known Member
Sep 17, 2010
1,800
96
48
Southern California
My 24'' Schwinn with the Stihl backpack leaf blower motor has a plastic cam and before I got the motor it served every work day for 5 years at 5400 rpms with no failures. I only replaced it because there is a higher power cam available and it does more than 8000 rpms now. It also has a centrifugally de-activated compression release built into it like a lot of the metal cams.
 

motorhedfred

Member
Jul 31, 2009
416
14
18
United States
My 24'' Schwinn with the Stihl backpack leaf blower motor has a plastic cam and before I got the motor it served every work day for 5 years at 5400 rpms with no failures. I only replaced it because there is a higher power cam available and it does more than 8000 rpms now. It also has a centrifugally de-activated compression release built into it like a lot of the metal cams.
I got to this post because I was searching for info and reviews on the Stihl 4 mix engines for use in motorized bicycles. Where did you find a performance cam for it?
 

msrfan

Well-Known Member
Sep 17, 2010
1,800
96
48
Southern California
Hey MHF, my motor came from a BR500 Stihl rated at around 3hp. I checked the specs on all their blowers and the BR600 was rated at 4hp. After checking both models parts lists, the only difference I could find was their use of different electronic modules, cams and carburetors. I purchased all three and it didn't take long to realize I wasted my money on the carb and had to get a much larger one from a chain saw. I don't have any specs on the different components but it runs strong with what I ended up using.
 

motorhedfred

Member
Jul 31, 2009
416
14
18
United States
Thanks for the reply msrfan. Wow, good detective work! Speaking of ignition, I'd like to run a hall effect, total loss battery ignition. Do you think the cam material could withstand having a shallow hole drilled into it to accept a small neodymium magnet to trigger it?
 

msrfan

Well-Known Member
Sep 17, 2010
1,800
96
48
Southern California
The cam turning half the crank speed would probably hold up. They have a compression release that takes up quite a bit of room. Depends on how large the magnet is and how it's attached. Were you going to modify the cam cover or make a whole new one for the sensor?