97cc Budget cam project

[mr.modified]

I need some more power out of my "super stock" 97cc motor, so it's time to make a budget performance cam using one stock 2.8 cam and a very old, very used westinghouse arc welder. I'm using the cam from my spare block for this experiment. The super stock engine will stay together until I get the performance cam completed, then I'll swap out the stock cam. First I checked my spare block to see what the cam looks like from the factory. It's got roughly .125 lift. I counted the valves as closed until they lift about .015 off the seat. Intake opens at about TDC and closes at about 22 degrees after BDC. Exhaust opens at about 33 degrees BBDC and closes at about TDC. The picture is a 2.8 cam next to a spare briggs 3.5hp cam that i'll practice on before I ruin the 2.8 cam. I'm not going to make the lift any higher due to clearance issues with my "hack job" head. I think I'm going to advance the cam a tooth (about 8.2 degrees) and add some material on the "back" side of the lobes. Then I'll keep checking things in my spare block as I grind things smooth...we'll see what happens...

 

[mr.modified]

Heres a picture of the practice cam in the vice after some welding and after a few seconds on the grinder. It looks bad but once you clean it up, I think it might work. A few more practice shots on the now destroyed briggs cam and we'll be ready for the 2.8 cam...:grind:

 

[mr.modified]

Ok, the budget cam is completed. I ended up setting the cam ahead two teeth instead of one.
Stock
Intake:Opens @ TDC -Closes @ 22 degrees ABDC
Exhaust:Opens @ 33 degrees BBDC -Closes @ TDC

Budget weld and regrind
Intake:Opens @ 32 degrees BTDC -Closes @ 24 degrees ABDC
Exhaust:Opens @ 67 degrees BBDC -Closes @ 22 ATDC

It might be a little too radical, but i'll try it anyway and see what happens. I can always grind it down some more. The intake probably should open a little later and the exhaust should probably close a little earlier. I'll try it tonight if the rain holds off.

 

[mhornfeck72205]

Welded a few of my own gx200 cams before I got one that worked well.. If you polish it well you'll be surprised at how well it works. Just keep checking the wear on the lifters whenever you do an oil change. Make sure the lobe is flat or has a wide surface touching the lifter that stays in a straight line down the center and doesn't go side to side. I've had no abnormal wear on my lifters or additional grinding on the welds on the lobes.

Let us know how it goes! Good luck.

Sent from my NookColor using Tapatalk

 

[mr.modified]

It works! I swaped out the stock cam in the super stock last night. I don't even drain the oil out to take the side cover off, I just tip the bike on it's side. I had checked to make sure the lift was the same in my spare block, but just to be sure before I started it up, I turned it over a few times to make sure nothing hit. I started it up and It runs pretty good. It seems to rev up quicker than it did. It will back fire now when you back off on the throttle, which it wouldn't do very often before. The cam makes it noticably louder due to the exhaust opening before BDC. Seems to have more compression when you pull it over now and it kicked back once when I tried starting it this morning which it wouldn't do before. Idle isn't too bad, just a slight lope. I'll get some video on here of before and after when I get a chance. I figure I've got about 12 hrs into the super stock now...Cam 5 hrs, Head 5 hrs, Intake 2.5 hrs, Exhaust 1/2 hr, Paint 1/2 hr, plus polishing the rod, removing material between the block and cyl, taking everything apart and reassembling. So far It seems to be holding up. I've got to find some steel and weld a scatter shield around the flywheel shroud somehow...

 

[r_chez_08]

Looks good, was considering doing this with my clone cam, just made ratio rockers instead.

Is the doodle bug motet cam ferrous (iron/steel?)
I have a Honda g100 which is meant to be the original which the doodlebug motor was cloned from, but it has an aluminium cam!

 

[JamnJM]

Billet flywheel & rod too. Please....

 

[chazdaddy]

"Billet flywheel & rod too. Please...."?

I don't think available, no market for it or ARC would make them. I assume not cheap to custom make flywheel and rod. I would love to have one that would safely turn 7000rpms, but not practical. :shrug: