5hp mild build...... performance cam?

markus

markus

Well-Known Member
#1
#1
I have to start planning the parts for a build. I need to try to build a 5hp, That runs strong and will not be too troubled by running higher rpms for probably a little more sustained than normal, and externally look like a stock 1967 4hp :oops: So that limits me on the carb to the old pull choke and even a hot dog muffler (I have a plan for the muff though)

This will be for a 1967 Fox campus, I do have the title for the bike so There is the opportunity to get it street legal. Not to mention we are relocating my mother from north FL to down here by us and if this deal goes though on a house we are looking to buy, she may live within a mile of me. I am sure I'll be running over there constantly! Not to mention we are in a great little area of our town on the historic side with slower roads, great parks on the bay and shopping ares etc., so something that can run in the mid 30's in a 5 mile radius is pretty doable.

Backstory out of the way Here's what I have collected so far:

Here is the original 4hp from the bike, which the new engine has to look like so I am stuck with an earlier style block with no oil sensor hole (so that means bushing case) block.


thankfully the OG shrouding is in good shape to redo and that tank is an NOS one I ran across awhile back (just bolted it on there to keep parts together in storage)

Here is what I bought with intentions to use for this awhile back:



It is a mid 80's 5hp engine that has some mods, The block is a perfect match externally ('cept for the 13's cast into the side by the breather ;)) This one is a ball bearing sidecover which does not match but that is something that will be hidden behind the clutch and guard so that is OK. It's been sleeved and is .010 over, the piston is a Wiseco and Horstman I beam rod with inserts. when I got it it did have what I think was a Lunati cam (this thing was built in the 90's If I remember right) but I sold it off The valves/springs that are there though dont appear to be anything special...they are not beat but I do intend to do all new up top to match a new cam. A possible downside is there is some porting done, maybe a little more open than needed for what I want to do. I found an NOS crank to use as well.

What I need to figure out is a good aftermarket cam for my app, or would one even be needed? I am going to do what I can to the carb and hopefully get it opened up a little, but I won't be able to achieve too much with the pull choke. for the muff I plan to drill out the center insert so it will as open as it can. As stated I would love for this bike to cruise at 35-ish mph with hopes that it could peak from there in the 40 range on a whim or if needed to get out of the way, yet still have good low end take off and power since I will have to deal with light traffic....sounds easy enough....but probably not :D

One of the other Campus bikes I had was also B&S 4hp engined bike. I would say it was happy mid 20's and would peak in the mid 30's before it started talking back....in and angry tone :D sounded like valves so that has me worried about using a stock cam, and valve train. Actual internal condition of that engine was unknown though. It appeared to have never been opened up and I had just set the points, cleaned the carb and went, so I'm sure it could have used some lovin' inside.

I don't have much experience with the briggs 5hp's other than tuning one up here an there I've never had much time inside or even on them to gauge how they run with different parts etc.. so I am a little lost in respect to how far the stock valve train will take you.
 
H

Havasu Dave

Moderator
#2
#2
With a stock block, it is not the valve train that will limit you with a cam selection, it is the kick back on the recoil, and then the lifter bores. The cam I have in a Tote Gote Raptor is hotter than the Raptor cam, but the cam card I posed here on OldMiniBikes got deleted along with the build. Note that the stock Raptor cam is hotter than the stock cam. I checked that too, but no numbers to report.

The kazoo carb- I went to a later model pulsa jet because it allowed mounting on that later tank, and used the later model choke lever as opposed to the push-pull button. A Raptor carb has no choke. Sorry for skipping around here.

The Dyno 94SS is very popular and doesn't require billet lifters or strengthened lifter bores, but does require new valves so you can start fresh with lash.

Also look at the 004 grind. Here are the springs for it. The retaining bits are on that same page.

Dyno says you can use the 107 with no special lifter mods, but it might be one to kick back on start. For sure the 108 will kick back, and damage your hand, and cause you to go to the doctor for a sprained wrist, and sell the engine, and get of mini bikes, and move to California. But it does make a hot rod engine, if you use a Mikuni etc.

Note that these cams like more spark advance, so you're going to mess with keys or adjustable wheels.

After a few years, I am still riding the Tote Gote, and winding out the engine against the torque converter like no one's business.
 
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delray

delray

Well-Known Member
#3
#3
one thing you could do markus is just advance the timing and install a set of stiffer valve springs(#16) little porting may help too and bike comes with a header already,so that's a plus. that would let the bike pull hard up to 4500- 5000 easy. one thing you need to watch for when purchasing a cam most are design to pull much higher in rpm's and your bike may not have the gearing you need to make this happen. so if you do get a aftermarket cam go with a very mild cam or just use the stock cam and just do the little tricks that I mention and that 5hp will feel like a little animal......:scooter:
 
Dr. Shop Teacher

Dr. Shop Teacher

#4
#4
@markus, I going with the Dyno 98-3, 18lb springs and a fixed ARC flywheel. The 98-3 is a junior stock cam and is rated to 6500. I'm hoping that it starts fairly easy. I'm using stock lifters and retainers on this engine. Nothing fancy but I will be able to swap jackshaft sprockets to gear it right. Hope this helps.
 
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