Sportsman 80 Build

[sportscarpat]

Hi Guys,
It's been awhile since I did a build thread. Recently I traded off one of my favorite bikes, a Sportsman 80 that even had one of the discontinued Harbor Freight 99cc engines. It was worth the trade as I kicked down the bike and cash to a friend of mine for a 1949 Ford F1 pickup. The bike was a beautiful machine with the best of everything. I rode it to work, all around town, and did the 90 mile Whizzin ride a few times. So, time to replace it with another work horse.

Here is the starting point, a Sportsman Flyer pedal bike which I call my "Super Cruiser". It started life as a no option Worksman Sportsman Flyer to which I added truss forks, panel tanks, fenders, and a Strumy Archer two speed kickback coaster brake hub and Brooks saddle. I pedaled this clunker to school (yep, school) twice a week and even stuffed my homework inside the panel tank compartment.

Sportsman Pedal Bike by Pat Dolan, on Flickr

Sportsman Pedal Bike by Pat Dolan, on Flickr

 

[sportscarpat]

Here is the engine mounting system and a fresh Harbor Freight 79cc four stroke. I set the engine up for the application by making a few mods.
1. Take stock engine and remove ALL external components.
2. Remove side cover to access internals and then remove the engine governor system and plug the holes.
3. Drill side cover for oil fill point.
4. Add stiffer valve springs.
5. Clean up the outside of the case to remove a few engine castings no longer necessary.
6. Add a proper clutch assembly designed for correct output shaft size and street rpm range.

Sportsman 80 by Pat Dolan, on Flickr

I like to take a piece of rubber hose, split it, and use it to properly space the engine mounting assembly with an even gap from the drop loop. This also keeps me from scratching the paint. The engine cradle, as I call it, is water jet cut from 3/8" aluminum plate.

Sportsman 80 by Pat Dolan, on Flickr

Here it is clamped in and ready for the adjustable secondary mount. Notice how this main mount ties in all the frame tubes. It is a structural member and ties in the downtube to the seatpost tube without touching the bottom bracket. Solid. This mount isn't going anywhere.

Sportsman 80 by Pat Dolan, on Flickr

 

[sportscarpat]

This photo shows the secondary engine mount. The main mount is fixed in position and this next mount carries the engine and has a full range of front/rear adjustment to allow for primary chain adjustment. Also shown are the pressed in bottom bracket bearing cups which will carry the reduction drive pedal crank assembly.

Sportsman 80 by Pat Dolan, on Flickr

Next up is the engine. I just quickly mounted it to see how everything looks. It will still get a vibration dampening rubber sheet between the engine base and adjustable engine mount. The entire engine mount assembly is laser cut stainless and tig welded together. You can also see the head mount bracket bolted down with the valve cover. This bracket will tie the top of the engine to the frame middle tube to keep the engine from moving around under load.

Sportsman 80 by Pat Dolan, on Flickr

 

[silverbear]

Pat,
This is so good, so well thought out. While I like the fast bikes, the scale of this one is just right for most of us. 79cc is enough or at least can be enough if it is done right. Do you think removing the governor internals is necessary or is it adequate to just disconnect and seal up from the outside?

Thanks for taking the time to do the build thread.
SB

 

[curtisfox]

Another AWESOME! build ,really love what you do.................Curt

 

[Venice Motor Bikes]

Awesome looking bike Pat!

I've been wanting to build another Worksman BTR with one of your kits & I think these pics are just what it's gonna take to get the ball rolling.

Do you think the mounting plate will fit a 212cc??

 

[sportscarpat]

Pat,
This is so good, so well thought out. While I like the fast bikes, the scale of this one is just right for most of us. 79cc is enough or at least can be enough if it is done right. Do you think removing the governor internals is necessary or is it adequate to just disconnect and seal up from the outside?

Thanks for taking the time to do the build thread.
SB

Hi Silverbear,
I would agree about the 79cc four stroke being enough for the bike. My experience is they cruise comfortably between 35-38 mph and can reach 45 mph. That is impressive performance for cruiser bicycle.
I have shown the process before on modifying the engine. I have also ran these engines without removing the engine governor assembly just to see what would happen. It didn't break but from looking at the assembly it would be best to add an external tension spring to it so it doesn't bounce around without load. By the time you mess with that it's just better to make the mods internally. Since I drill the side cover for the oil fill port I have to remove the side cover anyway, so once the cover is removed you may as well remove the governor, too.

 

[sportscarpat]

Awesome looking bike Pat!

I've been wanting to build another Worksman BTR with one of your kits & I think these pics are just what it's gonna take to get the ball rolling.

Do you think the mounting plate will fit a 212cc??

Hi Norm,
Thanks! I purposely built the mount so it will not fit the 212cc engine. Also, as you know, this frame has 110mm hub spacing so the wider width of the 212cc engine coupled with the narrower width of the 110mm hub is outside the range off offset available with my reduction drive. Finally, although the .090" wall steel tube frame is tough, as is the clamp in engine mount system, I never intended it to live up to the performance potential of the 212cc engine.

 

[sportscarpat]

Here is what the inside of the HF79cc engine looks like. Simple, right? The engine governor was sitting to the left of the crank and is removed in this picture. There is a pin sticking through from the right side of the cover that carried the governor plastic gear. I knock the pin out, remove the gear, then reinstall the pin to plug the hole. On the front of the case there was the throttle lever, part of the governor assembly, that was also removed. Once removed I tap it with a pipe thread and plug it. I really need to show the whole procedure to remove the mystery from the process.

Sportsman 80 by Pat Dolan, on Flickr

 

[fasteddy]

Hi Pat,

Thank you for the explanation and the photo's. Do you think this motor and frame combination would work with a sidecar big enough for an adult or would it be better to step up to the larger frame and the 212?
Anything over 25 miles an hour won't be done by me and it will most likely be in the 20 mph range. I just need the ability to take off with a passenger from a standing start.

The build looks great

Do you know yet if the salt flats are a go this year?

Steve.

 

[indian22]

Thanks for sharing Pat. It's going to be another beauty of a daily rider & performance expectations are impressive. Your going to stiffer valve springs mainly because your eliminating the governor & increasing the RPM range, no?
I've been thinking about building another small displacement 4 cycle motobike to add to my stable & your choice of the 79cc HF seems a good one to consider. Rick C.

 

[sportscarpat]

Hi Pat,

Thank you for the explanation and the photo's. Do you think this motor and frame combination would work with a sidecar big enough for an adult or would it be better to step up to the larger frame and the 212?
Anything over 25 miles an hour won't be done by me and it will most likely be in the 20 mph range. I just need the ability to take off with a passenger from a standing start.

The build looks great

Do you know yet if the salt flats are a go this year?

Steve.

Hi Steve,
If your not after speed you can change the gearing on the 80 to be a real stump puller. The 80cc motor would then be fine for what your trying to do.
As far as the salt flats go this year Speed Week was canceled because of poor salt conditions. Second year in a row. We are hoping World Finals, also an SCTA santioned event, will have better conditions. That would be Sep. 29th through Oct. 2nd. Of my two entered race bikes the 250cc machine is showing record potential. The other bike still isn't sorted out. We had five bikes entered under three different teams.

 

[sportscarpat]

Thanks for sharing Pat. It's going to be another beauty of a daily rider & performance expectations are impressive. Your going to stiffer valve springs mainly because your eliminating the governor & increasing the RPM range, no?
I've been thinking about building another small displacement 4 cycle motobike to add to my stable & your choice of the 79cc HF seems a good one to consider. Rick C.

With the stiffer valve springs the cam runs out before the springs, which is good. Based on my gear ratios and speeds I can get 45 mph so that means 6500 rpm. More than enough on the stock flywheel. So far I have found no gains using bigger cams. Actually my only fat cam was slower than the stock cam which tells me there isn't enough valve or compression to use the bigger cam. Also, I find the 99cc predator, if you can find one, is no faster than a 79cc engine. That's a lot of good information right there and it's all based on real world results.

 

[racie35]

You're doing something wrong if you added 1/4 of your displacement to an engine with no results..79vs99.
The worksman is cool though

 

[sportscarpat]

You're doing something wrong if you added 1/4 of your displacement to an engine with no results..79vs99.
The worksman is cool though

Just telling you my experience. The 99cc may have had a little more bottom end torque but not what I expected, and the difference wasn't worth the trouble finding the out of stock 99cc engine. With the stock cam and valve springs valve float is at 6500 rpm for both engines, and that is 45 mph.

 

[racie35]

I think you're relating rpm to hp....each will have different hp at nearly every rpm....so geared accordingly, the 99 wins the mph battle also.

 

[sportscarpat]

If an engine floats it's valves at 6500 rpm and it has a fixed gear ratio it's going to go a specific speed regardless of displacement. RPM is the limiting factor here and not hp. A 99cc engine should have more potential than a 79cc engine any day, and up to a valve spring limit of 6500 rpm the 99cc should have more torque getting there, so it should accelerate faster. That should make the 99cc engine feel more powerful, but that "feel" in these two stock engines, both with 18 lb valve springs, isn't much different. Would the 99cc win a drag race over the 79cc? It should. By the way, I wouldn't suggest pushing the stock cast iron flywheel beyond 6500 rpm. I put 18 lb springs on these engines, remove the governor, add my intake and exhaust and call it good.

I just looked online at the manuals for the HF79cc and 99cc engines. BOTH are rated at 3.5 ft/lbs of torque at 2500 rpm. Must be why I can't feel any difference between the two. Maybe the smaller engine has a different cam to stay at the same power level, I just don't know. What I do know is the 79cc engine doesn't feel, to me anyway, any different than the 99cc, and the manufacturers specs show equal torque ratings.

 

[racie35]

Sounds like you think a chevy 350 floating valves at 6500 won't beat your measly 79cc
99 definately has more grunt than a 79

 

[indian22]

Pat 6500 rpm by deleting the gov. & adding more robust springs sounds like an inexpensive way to obtain good performance from a dedicated daily cruiser. What carb will you select and at what rpm does the clutch come in? Thanks, Rick C.

 

[sportscarpat]

Sounds like you think a chevy 350 floating valves at 6500 won't beat your measly 79cc
99 definately has more grunt than a 79

What I said is a HF79 and a HF99 both running the same gear ratio at the same rpm limit of 6500 will both be going the same speed in mph.

I also said that both engines are rated at the same torque at the same rpm by the manufacturer. That spec is 3.5 ft/lbs at 2500 rpm.

Obviously for this same rated torque the stock 79cc is running in a higher state of tune than the stock 99cc. Maybe it's the cam or maybe it's the valves that are different, maybe both. I didn't measure them.