Mild I/C build advice

A

AJ Mac

New member
Hey team

I have a vintage minibike with a LO206 which I am planning on plucking back out and putting on the kart again and have managed to find an early I/C 5hp with duel bearing that I have started putting parts together for. The kicker is I am in New Zealand, flatheads have never been raced here and are only seen in lawn service haha so getting any advice or parts is a no go. On the plus side my girlfriend is American and we are spending Xmas in Virginia so I plan on filling up the suitcase and hauling some parts home.

My biggest question is around cam selection. I had planned so far (with the idea of pull start) to go with a 4.5 rod, Wiseco 1990 +.025. Replacing the valves with ss in stock size with billet lifters, cleaning up the casting imperfections in port and eyebrows.

Iv already got a original coil to ditch the points, a 6620 Arc flywheel and have spare LO206 carbs which I figured would pair up with the mild ports and small valves.

The cam I have been considering is the 112alt. Or will this be too big for the smaller carb and valves? Being on a minibike ripping around the pits I dont imaging itll be used at 7k all day long and most of its use will be pulling in an rpm range of 3-6k ish. The small valves and carb was with the idea of keeping it responsive in those rpm

Any help on cams or any other input would be hugely appreciated

Alex
 
The 112alt is not pull start friendly. That very cam is still to this day used for stock appearing class and tractor pulling. 112alt will involve clearance work due to the size of cam lobes, roughly .383" lift. I personally like said cam but it really starts to shines around 8k rpms on a short track.
I'd be looking for dyno 107ss for your application, but may be difficult to find one due to not being in production anymore.
Dynocams is in NC right down the road from VA. If you can manage to send them a stock usuable 5hp cam, they will make the grind for you😉
 
I really like the 112ALT. You’ll need to clearance the head for the lift. You can get it in tool steel or billet. I prefer billet. You don’t have to send a core in to get either of those but you will need to if you want a cast core, which is a bit cheaper. You can pull start it. I did it for years when I was racing back in the early 90’s because I didn’t have an electric starter. Just make sure to pull up on the the compression stroke before you pull to start it.
 
ktd said:
so what is the biggest cam you can run in stock block &valves
Click to expand...
.315" lift.

I'd steer away from the 112-alt without a remote starter. You might pull start it a few times, but you will regret it if you ever ask someone else to start you. :) The power band of the 112-alt (although it works great for short tracks) is well above your target rpm range.

107SS or even 94SS would be a good choice - still no compression release and a bit hard on the hands, but you can hand start it if you start on the compression stroke each time as suggested above.

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Brian Carlson
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I say .315" because that's the biggest you can go without having to do additional machine work for clearance in the cylinder head. Obviously you can go much bigger once you do some machining.
 
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