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May 24

Speeds on the red bike

6 comments

Since working on the build, I'm riding it a little, working out some small bugs, tuning & other stuff to make sure it will perform & work properly when it needs to.

 

I'm just running on the street in front of the house for now. I ride to Tractor supply, turn around & head back to the house while looking for "traffic" on the road. There's a lot of Highway Patrol, Colfax County Sheriff & City of Raton Po-Po around the area, so I'm trying to stay under the radar for now, literally. I figure they're already busy doing a good job, so why trouble them with trivial stuff like an old bald guy on a mini bike who may or may not be speeding.

 

Anyway, I'm still working on things & don't want to go out to the long road yet for a top end run, so little by little I keep adjust things, tightening, then run again after a couple of days. I did a run a couple of days ago & noticed that the drive sprocket hub was loose on the axle, along with the brake hub after the run. This was after a 53 mph run (6380 rpm), so I stopped, reset the screws, took things apart & tightened things up again.

 

Today, I decided it was time to try it again, so I warmed it up & ran again on the same stretch of road. This time things have stayed tight for the run & I upped the rpms a little bit to 7250, which ends up being 63 mph. Little by little it's getting there. There's plenty of braking available still with the disc & twin-piston hydraulic caliper.

 

I've posted the proposed fix for the loose hubs (yes, they will get loose again) to the jackshaft-axle sub-heading on the forum, so take a look at what I'm going to do when the parts arrive next week. It's a simple fix which should solve the problem on this part of the axle.

May 26

One step forward & 2 steps back. Tried a new Inferno Flame clutch & went up to a 14 tooth sprocket on the "outboard" mount I have to use on this bike. It's much slower off the line this way, noticeably slower as it pulls to hook up. Engagement starts at 3200 rpms & locks up at about 3500-3600. I'm running the "2 black - 2 white" spring combination for now without any weights, just to see how it works. So far, I think I may be over-geared on the top end with this setup. With a 13 tooth driver, the final output with the jackshaft setup is 6.46:1 (13 tooth driver on a Max Torque clutch, 18 tooth jackshaft, 10 tooth 420 sprocket to the 48 tooth live axle sprocket). This pulled really well & wound up without any flat spots, bogging or drop off on top end. It was still pulling over 7000 rpms when I ran out of room on the pull.

 

When I went to the Flame clutch & 14 tooth drive sprocket (the final drive ration is 6.171:1 with the new 14t setup) the launch is much softer & the top end won't climb past 6300 rpm on a small hill. I'm wondering about 2 things here:

1 - I've hit the top of the torque curve & can't build enough r's to top out with the new gear ratio.

2 - My tune is off a little. I haven't correctly fine-tuned for this higher altitude with the main jetting to get all the available power in this motor. It pulls well enough to 6300 rpms, but then it's like hitting a wall when I run up against the hill. There should be 2000 more rpms in this motor for the top end still, but it's just not there.

 

OK, so I've ordered a couple of new sprockets from BMI (13 & 12 tooth) & hope to see what's going on. I like the Inferno's quick-change setup. I can swap the drive sprockets out in a couple of minutes, or do a complete spring & weight change with things pretty quickly, to shift the engagement on the torque curve. I'm going back to a 13 tooth driver for now on the new Blaze clutch, without changing the tune at all, to see if I duplicate the top end pull with the old clutch. If that's the case, I'll play around with jetting to see if I might be off one jet size with this higher altitude & thin air.

 

I pulled the plug, cleaned it & it looked decent, but... It's the same one I started running with this motor at lower altitudes, so a plug test still needs to be done at this altitude. I can feel the motor now, after having run it for a while & understanding the Mikuni jet setup, but more testing is needed to determine the correct jet for up here. I may order a new plug (the Autolite 3910X) which is working well. This is a "cold" plug but works very well in my motor, no fouling or carbon build-up with the high compression motor & 100 octane gas. People run these plugs in stock motors & they will foul due to idling, rich mixtures & bad jetting. Mine likes this plug a lot.

 

For now I'm waiting on new sprockets so I don't change too many variables at one time. The process of elimination continues. Change one thing, see how it works then if it doesn't, change back & do something different to see if that's the problem. And so it goes...

May 27

Had some time yesterday, so I looked at the jetting chart for altitude. I must have read the chart wrong, as I had dropped down 2 sizes (130 down to 110) in going from 2600' in Tucson to 6500' in Raton, so I went up one jet size to a 120 main. It pulls better at top end & WOT now than before. It was starving for fuel slightly with the 130. Will still play around with sprockets when they arrive & fix the hub-to-axle connections, but I need to do a real speed run today on a flat pavement to see how things are. It will be a first, with enough pavement to see where the top end really is now with this gearing & a better main jet.

 

Yesterday it was blowing again between 25 & 30 mph, so it's sort of hard to figure out where I am with that much headwind or tailwind. Uphill & 30 mph of headwind was bad, no way to see how it was doing with that much wind & the long hill. Downhill & a tail wind would have put me into town with a 45 mph speed limit at way too much speed.

 

Here's the screen shot to show where things are now, with the 120 main jet & a more or less short & level stretch to run up the rpms. The low average was due to running around on back streets to let the engine come up to temperature prior to the run. Hoping to do a little bit better today on the flat, long pavement. There are few rises & dips in the stretch I'm going to run, but it's out of town & there shouldn't be too much traffic on the road.

 

62

 

May 27

Well, it's good news, bad news today. First, the good news. I managed to get another 1 mph out of the bike with revised jetting & the same gearing. It's nice & stable at higher speeds & ran well, just not up to expectations, since it seems to hit a wall at 63 mph. Just not making the HP it needs to punch a faster hole in the air. Gearing will be next to take advantage of the higher rpm capability of the cam, carb, piston, etc. with this motor.

 

Whoopee! one whole MPH gained on this morning's run.

The bad news was this happened at some point on the run. I had braced the header to the head (like I did before on the other bike) since it needs to be supported or the weld will snap & the pipe will come loose from the mount. I had a little misalignment (0.06") which was fixed with the bolt to the head being tightened a little more than necessary. Also, I used a stronger piece of steel I had in the shop to make the brace, it's about 3/16" thick. I thought the head was plenty strong to allow for the wiggle & vibration, but I guess I was wrong. The head is actually very thin around the bolt hole, so here's what I found when I put it up on the bench in the shop to clean it up after the run.

 

At least the bolt didn't come loose

Here's the head after pulling it off the block.

 

A small hole where the bolt was attached, no JBweld on this one.

I've ordered a new head from Ebay & am waiting to start porting it (again) once it gets here. Nothing major, just some cleanup on the runners & it should be good to go. Thinking about the header bracket & where I located it on this motor. Don't want to break the new head the same way, something different may be in order on the next head. I'm open to suggestions.

Jun 1

Got the head, ported it & put the motor back together again. Checked piston to valve clearance just to make sure the casting was ok, but there's still enough room at the exhaust valve. The intake is fine, the exhaust valve is where there's a clearance issue with this build, the Bullfrog piston, longer rod & domed head, but no problems.

 

I did two things differently after breaking the last head. I changed the bracket location to be at the lower head bolt. The first shot shows the lower head bolt & new bracket mount location. I kept the fan shroud in place & just notched it for the bracket. With the bracket at a wider angle now from the header, a better fit at the hole & different point, it should be better.

 

Second thing I did was cut off about 4" of the header, to lessen the loading on the bolts & bracket. It will (hopefully) be less weight flailing around on the header & help it keep from breaking things again. I'm still thinking about adding another hard point at the frame, but am holding off for now until I see how it goes. If I add a bracket at the frame, it needs a sliding mount & some type of damper to soften the connection, since the engine can create a little bit of flex as it's running. The motor still needs to move for chain tension, so a slotted bracket would have to be fabbed.

 

4" shorter on the header, should help with the vibration

I did a quick run in front of the house. The new sprockets showed up for the Inferno Flame clutch, so I swapped the engine sprocket back to 13 teeth & changed the jackshaft primary sprocket to a 20t. It pulls a bit better with this lower gearing, it's now at 7.38:1 (was 6.46:1 with 14t & 18t), but it still feels like at 7400 rpm it's not breathing correctly. At that rpm & wind load (55 mph) it still feels like it's starving a bit, but I still have to decide if it's starved for fuel or just running out of air due to the elevation.

Jun 2

Had a suggestion from a friend's son, drill out the gas cap for better venting. It worked, runs up to speed now & pulls better on the top end. I guess that's why it was feeling starved for fuel. It couldn't quite get enough at higher speeds. It felt like a fuel filter being plugged. It's fine around town, but starved on the freeway. Only a slight problem today when I ran it up to 8720 rpm. Here's a picture of what happened. I guess I finally got the rod to stretch a bit at that higher speed.

 

A small amount of piston to plug interference, just a kiss

I'd pulled the plug to look at it after a few runs for tune & it looked OK (maybe a bit lean) but it had a shiny spot from hitting the piston. I indexed a new "X" plug into the head, then ground it down a bit where it would hit the piston if I over-rev again, so it's all good (for now). If I pull the new head, I'll have to carve out a slightly larger dimple in the dome for clearance. For now, it should be fine, but I'm going to shy away from anything over 8400 rpm as my upper limit.

 

You can see where the lower-left electrode has been mashed a little & deformed, it was enough to close up the gap to about 0.012" from about 0.035" so it was a fairly hard hit of over 0.020". This didn't happen at 8400 rpm before, so that's going to be my limit from now on. Good thing it's a forged piston (inside the bottom it says Arias) & made very well, a weaker piston could have come apart from the hit, but Bullfrog makes a good piston. Hoping there are no fractures in the head at the plug threads or in the dome of the piston, but time will tell. The piston is pretty thick & heavy up there, so I think I've just "forged" the shape of the plug into the dimple. The hit in the plug dimple would be at about 2:00 in this picture.

 

 

 

Let me say here, this is NOT the way to test a motor for interference. I guess I finally found the upper rpm range, in a way it's good to know, but everything pushed long & hard enough will ultimately fail. It could have just as easily destroyed the motor on a run like that. I still need to check a few things over on the new head, but for now I'm pleased with the output from this run. Top speed was a calculated 65 mph with the lower gearing (phone app wasn't running) & I was keeping up with freeway traffic (I was on the frontage road running next to the freeway which has a 65 mph speed limit in this area, I was not on the freeway).

Jun 3

I really need to stop at this point, take a step back & see what's happening inside the bottom end. Having a bad journal on the crank to start the build was something I should have thought more about. It was nearly .005" out of round when I checked it. I spent a lot of time wet sanding with WD40 to get it close enough to run & not spin a bearing when I pulled the rope & it started the first time. Now it seems like a minor miracle that I got away with what I did for this long. I guess I did things mostly right on the basics, but this can't last for ever. Sanding the journal to "mostly" round? Stock valves? No experience on one of these motors?

 

Here was the original build on the OMB forum from 2 years ago. Remember, this was my first build for one of these motors, so there are probably things in the thread which aren't right. Fortunately I had some help from some very good people on the build.

https://www.oldminibikes.com/forum/index.php?threads/hemi-build-started.146490/

Will look into the new motor under the bench, (another 60363 Hemi from HF I've been sitting on for a while) un-box it & check the crank to see if this one is round & not an egg at the main journal. I'll play with the new head I ordered that isn't here yet (yes, I ordered a "spare" head), get some better valves & keepers for it, then order some new rod bearings (maybe a new rod also?). The bottom end in the red bike is as it was built 2 years ago. I've pushed my luck way past common sense & into the realm of "GOD protects fools" now.

Need to look at the piston as well, to see what kind of ding the plug made in it & see if I floated the valves a little. The exhaust valve would be the one which would have made contact with the head, but anything's possible with the rpm's I turned on this last run.

So, for now the red bike has done a pretty decent job. It does track really well at speed. It's absolutely stable, steady & no sign of a wobble at all over 60 mph. I did crank down the steering stabilizer prior to that run, to add a bit more friction in case of a death wobble, but it wasn't really necessary. I guess the geometry in the front end is good & was done right. If you're interested, the layout was done with a 35 degree front rake, 10" steel rim & Michelin scooter tire, 5/8" axle, & 26" wide bars to the outside of the grips. The front trail dimension is 5 1/4" which steers pretty well, but due to the 3" frame clearance, it's rubbing the pegs on anything but a shallow turn so it's hard to say how nimble it really is at slower speeds & tight turning. The pegs drag too easily.

 

The brakes are very solid, just about power brakes with the twin-piston caliper setup. The total wet weight of a hefty 127# is up there, but it's better than being too lite & bendy. At higher speeds you want a solid frame. The 1" DOM tubing was a good choice for the frame & 7/8" DOM for the front end is plenty strong enough, as the tubes are relatively short.

 

Back to the shop today for more looking into the motor & seeing what the bottom end looks like.