Max's Phat Briggs Bike Build

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msrfan

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Sep 17, 2010
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This is Max with his Phat cruiser. He has a 3-4 hp Briggs motor for it and we made top and bottom mounts and had my grandson weld them in. He's looking for a fuel tank and has already purchased a 3D Motorsports clutch for it. He got the 428 (1/2'' pitch) sprocket and will use a hub adapter with sprocket on the rear. I sold him a front drum brake and had the button welded to hold the plate from rotating. Tons of work left to do, but he's made a good start.





 
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msrfan

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Sep 17, 2010
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Southern California
Max got a 4 stroke kit for Christmas and put it on the aluminum frame we were originally going to use for his Briggs build until we realized it wasn't steel. He got it running but had to work out some problems, like some orange junk it the fuel tank that made it's way into the carb. Wouldn't run without the choke on. He new it needed more fuel, so I told him how to clean the jets and it finally came to life. He rode it over to my house without brakes (about 6 miles) to get help hooking up the coaster brake arm to the frame. He had it bent way out to clear his sprocket and it was about an inch out of alignment. His vise at home is just screwed to a flimsy table, so using mine we straightened it until it lined up with the frame and of course now it rubbed the sprocket. I ground the square edges off the arm but didn't go far enough to weaken it. Then I started removing material from the inner diameter of the aluminum sprocket until it cleared. I used Dykem to check the rubbing areas and took off the high points.











I suggested axle adjusters and gave him washers to put under the nuts.




He showed me the belt on his motor was about 1/8'' out of alignment (which is considerable on such a short belt). We replaced the too thick spacer behind the large belt sprocket with a thinner one and now it wont wear out so fast. While we had the rear wheel off we widened the frame so the chain wouldn't rub anymore. We pounded a 2 X 4 in it until it was wider about 2'', then using Irwin clamps, squeezed it back together with the board still in it. That gave the desired clearance. He noticed some bolts missing from his POS kit supplied motor mount. I forgot to mention he never had a pedal chain on it because he knew what would happen if he tried to pedal backwards with the brake arm unattached. I cut sections out of the front and rear castings until they would swing enough to fit the frame squarely. We replaced the allen bolts with cap screws that had washer heads. Now the motor could be raised enough to clear the front pedal sprocket. Now his air filter (which he was running without) will fit without rubbing the frame. His spark plug was white, so I recommended putting his muffler back on and taking some more plug readings and compare with his friends with the same motors. With the engine higher his chain was too short. I didn't have any 415 chain to add to his, so I pieced together a 420 until we had the correct length. The pedal chain he brought had to be lengthened also. Luckily the length fit nicely when the drive chain was the right tension (without a tensioner).






I made a brake arm strap from some heavy banding I had and punched holes in it. He had removed the stock muffler in favor of a short curved pipe that hit the frame. I told him to add about 8 inches to the pipe and if he opened the mounting holes just a bit, he could twist it off the frame. We also replaced missing hardware on his seat so it wouldn't fall off. A small job of hooking up his rear brake became 3 hours of non stop repairs. Free parts, free labor. These kids have it too easy. Good thing I love to work on motor bikes. He texted me when he got home and said it was so much more solid and smoother riding than before. Max planned a long ride to Newport with a bunch of his buddies and decided to put his stock muffler and air filter back on. I told him to get a mirror and hook up some front brakes. He texted me again and said it had more torque and ran smoother in stock form. Still waiting to hear from him to see how his ride went. He'll probably come back over soon for the front brakes. I wonder what other repairs are in store for me.
 
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culvercityclassic

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Sep 27, 2009
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Culver City, Ca
Your a good guy for helping these kids, they may want to work with their hands someday for a living vs the boring desk job. You seem to keep busy being retired...lol

I have one of those motors on a bike and did not like the way it ran so I swapped out the carb for an NT from gas bike and wow what a difference, came with the intake manifold too.
 

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msrfan

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Sep 17, 2010
1,808
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Southern California
Yes, I'm twice as busy as when I worked for HB, but it's my own hours and I choose what I work on.
Max mentioned getting an NT carb when he was having trouble with his. I'll tell him it made a big difference for you. He says his is 49cc.
 
runnermike

runnermike

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Nov 18, 2012
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I think this is awesome! Teach them young. I have a lot of men that work for me that do not even know how to use simple hand tools.....crazy!
 
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msrfan

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Sep 17, 2010
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I know what you mean Mike. I've dealt with educated engineers that couldn't come close to building what they design.

Max's little motor keeps sliding back on it's mount slacking the chain. The 4 6mm bolts securing it keep coming loose, so he put a block behind the motor and that helped until it fell out. He's trying shakeproof washers next. If it still moves, I'll have to make him a tensioner that will hold it in place.
 
MEASURE TWICE

MEASURE TWICE

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Jul 13, 2010
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I use external star tooth washers backed up by a fender washer on the allen wrench drive bolt up from the bottom of engine platform. External star tooth washer grab very well in contact with the bottom of the engine platform.

The opposite side of the bolt with the threads I use a flat washer and a split lock washer and then the nut.

I also use this method on an adjustable height jackshaft where it sets chain tension between a dual jackshaft system. Using a belt and lots of tension it still held in position. I'm no longer using belt except from one of the jack shafts to a rear wheel sheave. Very small diameter belt drive with v-belts slip too much.
 
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MEASURE TWICE

MEASURE TWICE

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Jul 13, 2010
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I looked up shake proof washers and so I see they are what you will be trying next. The external star washer is one in the same. I noticed that they have an combined external / internal star tooth washer show on the web. Never seen one before.
 
Tony01

Tony01

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Nov 28, 2012
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Nice Dale, any ideas to get a little more performance out of those motors? Got a local kid here as well, same motor but an aluminum frame with the long ss tank in it, and everything on it was messed up when I met him. Lot of red flags! Loose/rattling shorty front fender, threadkess headset completely loose and moving, throttle stuck like a cruise control, disc pads worn completely to where th mech brake wouldnt engage the disc, header bolt broken and hanging on by the other one, etc. well I took one look and said "those are probably m5x.8" and the next time I saw him gave him a set and they worked. We did a brief ride thru one college campus one day and his chain jumped, so we rolled back to the coffee shop and I found he had a messed up half link missing the cotter pin, chain loose even with a tensioner, so had him remove the tensioner and fixed his chain... not so fast; he said it was 420 and so I said HEY I HAVE ONE MASTER LINK FOR THAT!! and of course it didn't fit cause his was actually 41, so with the bare minimum of tools supplied by another customer hammer, socket, etc took out the half link and assembled his chain solid.

His gas tank was extremely loose too and so I told him which metal straps to buy a such. We both thought it was an aluminum tank and after a lot of hard work putting the first two holes in I tried getting screws in, and the tank stripped em out and we realized it was stainless, ended up filling the holes with jb weld and using gorilla tape to hold the tank.

He's ordered an agk exhaust for it with the can muffler on it but I suspect it still has the baffle inside it; if so we'll be cutting it and removing the baffle and welding it back up. Hopefully get him to cut some stuff with the angle grinder, like his steerer tube which is too long to adjust the headset with. I will let him know about the NT carb. Whatever it takes for him to at least hit 35mph... the speed at which the clutch locks up on my 212....he says it tops out about 25 flatland and 10-12mph uphill... why not just get a nice lightweight pedal bike at that point right....

He calls my bike "the beast"... I been trying to get him to build a real bike... I have a Briggs 5hp sitting right here, a carb that'll work and enough metal to make it happen; just need a steel Schwinn and about $300.
 
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msrfan

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Sep 17, 2010
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Hey Tony, I haven't messed with threadless forks yet, but I hear you have to use the perfect size spacer to get them to not wiggle. As far as performance mods, I heard AGK may profile the plastic cams for more power. I think you're on the right track with modified exhaust and different carb. I've also seen 2 others that the primary drive belt was not aligned because of a too thick spacer behind the large pulley. Looked like the kit manufacturer cut them from water pipe. The mounting bases are horrible. By the time they make them fit every bike, they don't fit any bike without trimming and better hardware. Also some are plagued with broken clutch springs. 2 of the kids are locked up solid and run and jump on the bike to start. They won't get off long enough to fix the problems. So the biggest problem I see with these bikes are improper mounting and lack of maintenance. With their low power output, final gearing is more critical. May have to experiment with different rear sprockets. I'd wait and see how your mods work out though. Oh, and I've seen caliper brakes adjusted so tight that they drag, and crooked wheels don't help either. Like any of these projects, you need to get the bicycle squared away so it rides efficiently and stops well so you get all you can from the motor. Keep plugging and post your results.
 
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msrfan

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Sep 17, 2010
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Southern California
Max came over yesterday with his bike and we worked on the motor. Set the valve clearance, crank end play, torqued the head down, bolted it into the frame and put the flywheel on with a starting cup long enough to hear it run on starting fluid. Sounds great without any exhaust components. He bought Cyclops tires. Next we'll balance the flywheel and heat and bend the pedal crank to clear. We may have his running before Dave's Briggs bike. Looks like we may go with the clutch on the motor with a double sprocket jackshaft on the seat down tube. He has a rear hub adapter and sprocket already. Just called me and said he has a throttle, cables and levers. Moving right along on this one. Looking for an inexpensive late model Whizzer tank to finish the look he's after.





 
scratchbuilder

scratchbuilder

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Jan 17, 2015
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Hey msrfan, you mentioned balancing the flywheel. How do you do that?? My 3.5 Briggs has heavy vibs at just off idle then smooths out after another 500rpm's or so.
 
scratchbuilder

scratchbuilder

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Jan 17, 2015
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ca.
Great thanks. Ok by lower part, that means as it stops it leaning to the heavy side and when enough metal is removed it just stops resting level....
 
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