The motor on the red bike

Slow to gain members & learn this web software, so I'm putting in a post about the motor on the red bike to show what I did & at least have one post in this area. Please bear with me on the software, it's a PITA to learn.

I started with a stock Predator 60363 (hemi), not the conventional motor (wedge head) for a couple of reasons. The hemi has larger factory valves, a hemispherical combustion chamber and heavier 5.5mm valve stems. It's the same basic block, but the head should flow a bit better in general and can make decent horse power. There's a bunch of people who don't like this motor type, but I decided to go with the hemi style anyway. It turned out to be a good choice for me.

Here's the basic motor build

Black Mamba cam 0.275" lift, 26# springs, chromoly pushrods Bullfrog's pop-up 11:1 piston + 0.020" ARC billet rod

0.027" head gasket ARC billet flywheel with 32 degree advance 22mm Mikuni VM22-133 24" X 1" OD header

I used studs for the head & block side cover. They're glued in with red Loctite, so it's a bit better than the factory bolts for clamping & holding pressures. So far it's holding & working well, no leaks yet or blown gaskets.

Studs in place

The biggest problem I had with the build had to do with the main journal on the crank. It was ground out of round by about .004"-.005". Wonderful Chinese precision on the journal, to be sure. Nominal is 1.188" diameter for the ARC rod & bearings, but this one varied from 1.189" to 1.194" so it was egg shaped from the factory. I sanded it by hand with WD40 & Wet-Dry, paper to get it as close as I could. It took for ever, but I'm glad I used the plastigauge & digital caliper. This motor would have been junk the first time it was fired & wound up too tight. I finally got it within about .002" at all spots & called it good.

I spoke with an engineer at Bonneville from the Indian Motorcycle Company about it that year. He said with the slight out of round, it would act like a paint brush wiping the crank, but as long as the lubrication was good, it should work. He seems to have been right. Since I don't turn sustained high rpms, so far it's running ok up to 8400. I'm running Mobil 1 in the 5W-30 type with good results, but I should still send in an oil sample to a lab see what's really happening inside this motor.

Sand paper, stand & "shoe shine" motion to work the crank down

The crank endplay ended up at about .010", which is just about right. Too tight & it will blow the side cover gasket, too loose & it can move around too much and wreck things in a pretty nasty way. I made a crude end-play gauge with a Horrid Freight dial gauge that attaches to the block. It's good enough to give a true reading, close enough for one of these motors spinning well under 10,000 rpms.

I did a little work inside the intake & exhaust runners. nothing too radical, just smoothed out the edges, opened up the shelf areas a bit & then lapped the valves to make sure they were tight on the seats. I didn't change things too much (my first attempt at porting) but did remove enough metal to open the runners a bit without slowing down the airflow by getting things too big for midrange torque. If you open the runners too much, it can help some with the top end, but you will sacrifice some of the mid range due to lower air speed through a bigger hole. It pulls pretty well from about 4500 & up.

Seats lapped for a good seal, ports still rough

Had to grind the crank a bit to avoid the cam, just a freehand job on a belt grinder, but it's enough to pass & not hit as it swings past the tight spot.

The shiny spots are where the Black Mamba cam would have hit, so I took down both sides, "Balance, we don't need no stinkin' balance..."

The piston in place, checked deck height & valve to piston clearance. There's enough so far. This piston is cut for much bigger valves than I'm running now, the stock valves look small compared to this cutout. The squish area at the edges ended up between .040' & .050" with a .027" head gasket, so that's where it stays. There's .060" at the intake and more at the exhaust valve with the factory head torqued in place. All I did was lap the head on a sheet of glass, to make sure it was really flat for the gasket.

Valve cuts & spark plug dimple

Made a pulley/tightening setup for the flywheel nut. This keeps things in place so the crank can't spin when tightening the nut with the amount of force it needs.

Holding the crank to lock the flywheel nut in place

Here's the motor prior to hanging the fan shroud. The carb in the picture is the VM22 "Chikuni" I started with, but it was soon switched over to the genuine Mikuni. Much easier & faster to swap-out jets on the real one, much better made in general. You don't have to drop the entire bowl on the real one, just unscrew a bolt, replace the main jet & then replace the bolt.

I'm still running the stock ignition & it works pretty well. No trouble with it at this point, so I'll keep it going as long as it's still doing the job. Not sure what the upper limit is with a factory coil. Anyone know?

I was shooting for a reliable modded motor with more HP & higher rpms. This one seems to be doing the job pretty well so far with no leaks, problems or disasters. I buy 110 octane VP leaded fuel, then cut it 50% with 87 octane unleaded. This combination gives me about 99 or 100 octane, so it has never pinged or knocked. Not sure I'd want to have this happen at 8000 rpms... Here in Raton I'll just go to the airport & buy AV gas to mix down to 100 octane, better safe than sorry.

Running in Tucson & Phoenix I was using a 130 main jet, after moving to Raton at 6,500' I've had to drop down to a 110 main jet, but it's pulling pretty well, even with the thinner air. After a couple of real runs, I'll pull the plug to see how it looks. At least it won't get up to 115 this summer, maybe 95 a day or two, but that's about it for heat.

3 comments

noseoil

Jun 01, 2019

110 jet was too lean at 6500' so I went to a 120 main. It's still feeling a bit starved, but not sure if it's starved for air or fuel with this thin air & high altitude. At 7400 rpm now it feels like it's stopped pulling, which is 1000 rpm below what I was getting at a lower elevation. Will have to pull the plug after a bit of running & see how it looks.

noseoil

Jun 21, 2019Edited: Jun 21, 2019

Here's the oil analysis on the original motor after running in the desert, hard pulls past 8700 rpms & general abuse. Really pretty good, all things considered. It's a PDF, so not sure it will work...

LAB NUMBER: L29654 UNIT ID: RED BIKE-MOD 1

OIL

REPORT DATE: 6/19/2019 CLIENT ID: 144585

REPORT

CODE: 20/32 PAYMENT: Prepaid

T MAKE/MODEL: Predator 212cc OIL TYPE & GRADE: Mobil 1 5W/30

N FUEL TYPE: Gasoline (Leaded) OIL USE INTERVAL: 10 Hours

S TIM: Our averages for this type of engine are still under construction, so trends will be the best way to

T gauge internal wear. As it stands, aluminum and chrome could show excess piston and ring wear. They

E could also be from wear-in, or this might just be the norm for your engine. Silicon is from harmless sealers.

M The high level of lead is mostly from fuel blow by, but it does mask wear to the bearings. The oil itself tested

O well, with a viscosity in the 5W/30 range, no evidence of fuel or water contamination, and low insolubles. If