1350cc Pushrod bike

[wobblywalrus]

Jim, several posts ago you mentioned the mach # for a valve.  Could you explain this for us backwoods folk?

[JimL]

I was poking around on some good engine build sites, and ran across the info about piston speed and it's effect on peak engine power.  I took that info and went to some of the ex-TRD fellows and learned more about it.  The bottom line is that piston speed decides how fast the air is drawn through the intake port (peak speed is the kicker, apprarently).  If the ports are small (which boosts flow speed into the cylinder at lower RPM....good for trucks), the airflow becomes too high when RPM gets high.  By porting the inlet (bigger) we increase the volume available, while keeping the airflow speed down (same effect as the inlet for supersonic jets). 

If the airflow reaches Mach 0.5 (I think they actually hit 0.522 on some engines), the reversion wave (return pressure pulse from closed intake valve) meets the incoming air at about the same speed.  This puts the intake port over Mach 1.0, and the air (at that point and also momentarily) becomes non-compressible (it stops).  Because horsepower is (in the end) limited by RPM (normal aspirated engines), the stroke has to get very short to keep the piston speed down.  Lower piston speed keeps the peak airflow speed from going past 0.5 Mach, for a given port and valve size.

thx, JimL

I was told that the NASCAR engines are butting up against the Mach number, running in the 9200 RPM (or a little higher) range.

My engines are extremely short stroke (the 500 is only 2.047" and the 673s are only 2.48"), which lets me spin them pretty high WITH the new larger ports and valves.  Until I learned about the Mach number, I didn't realize how much small increases in valve size could matter.....it adds available RPM, and that starts multiplying the Horsepower calculation.

I kinda' jumbled the sentences....there are folks on here a lot better at this engine stuff, and perhaps they'll straighten me out a bit.  Another lesson about learning lessons too late....spent too many years playing with motorcycles and guitars.... to bother learning what I needed!

[wobblywalrus]

These modern engines are new to me.  My specialty was A65 BSAs and unit construction Triumphs.  The new Triumph is a short stroke 4 valve per cylinder engine.  Simply porting the head and adding 1mm larger intake valves made a real big difference at high rpm.  Maybe you are on to something.

[JimL]

Significant change in direction, today.  The belt drive was going to be a big problem due to cantilever of the loads.  I decided to revert to the original plan of inline spur gears.  I've already cut the motor plate (after fitting a 1.75" tool-stock strong-back on the lower edge), I've cut the engine cases, and mocked up the center gear.  The photo shows a pair of clutch baskets, but those will actually be just the gear, as the one shown between them.  Also, this method will completely enclose the primary drive system, eliminate multiple seals, etc.

Need to tear down some engines and get more clutch basket gears pulled off.  This will move along quicker, now, and a lot less pieces to make!

JImL

[Rex Schimmer]

Jim,
I like your plan about using a third clutch basket gear. What do you plan to do about the clutch? (if you have already said something just tell me to read the first part of the thread!) Those old diecast baskets have been known to fail and now you are doubling the load. I designed a clutch basket for the old Honda 500 single back in the 80s, they had a habit of breaking off the ears if you added a little horse power, a friend of mine, Jim Rodhen had a machine shop and made them out of 7075-T6 for the White Brothers, they never failed. You may want to consider something like that.

Rex

[WhizzbangK.C.]

Jim,
I like your plan about using a third clutch basket gear. What do you plan to do about the clutch? (if you have already said something just tell me to read the first part of the thread!) Those old diecast baskets have been known to fail and now you are doubling the load. I designed a clutch basket for the old Honda 500 single back in the 80s, they had a habit of breaking off the ears if you added a little horse power, a friend of mine, Jim Rodhen had a machine shop and made them out of 7075-T6 for the White Brothers, they never failed. You may want to consider something like that.

Rex

A friend of mine had the same problem with a H-D Sportster clutch, very similar set up, when he put nitrous to a big bore kit. No aftermarket parts available then. We cured it by turning an aluminum sleeve to surround the fingers. Very light press fit after turning the outside of the fingers on the basket casting true and tig welded to the fingers and hub. Never had another problem and it was a cheap fix. 

[JimL]

Thanks for the tip, fellows.  I can sleeve the basket ears.  Fortuanately, the Silver Wing baskets are pretty decent, due to the heavy touring bike/shaft drive package.  It has a full set of shock spriings between the gear and the basket (just like a good clutch disc).  These were there to smooth out the impacts onto the ears.  I have one that is brand new (springs are nice and snug) which will be the clutch pack for this bike.... new parts always last a little longer, at least.

Whew....one thing after another!!

JimL

[JimL]

A good shop day  , and my gear train is together and spinning smoothly.  I used 2 35mm, double-row, ball bearings in each coupling gear.  I cut a small groove in the center of the gear, then sandwiched a piece of welding wire between the bearings.  With the sides of the inner race shimmed into place, the gears will not be able to slip sideways between the plates.

The shafts are fixed (made from 15mm shaft stock) and mounted in double-shear.  Both coupling gears are now completely carried by the motor plate (which includes a carrier that is fitted into the case cavity, as shown in one pic).  This allows either engine to be removed without disturbing the gear drive package. The outer 1/4" steel plate is also serving as an additional stiffener, for the engine plate.  All of the bolts are shouldered (1/2") for precise fit.

In the photos you can see the rear gear shaft sticking out long (have to cut it off and make a retainer).  The forward gear shaft is still long on the backside view.  The primary drive will be covered with a single large cover, and the back side covers will be three pieces with a seal on the shaft (though the shaft does not rotate).

Gotta' hustle....still a lot to do.

JimL

[Rex Schimmer]

Jim,
What is your plan for lub on these gears? Making a case to enclose all of this looks to be a pretty daunting challenge (that how you say Pain in the A$$). Any thought of maybe some dry lube treatment and then some total loss lube? Obviously with some sort of shield to prevent any oil on the salt.

Rex

[wobblywalrus]

There are a lot of horses passing through that little clutch.  Lubed gears and a dry clutch might be good.

[JimL]

The gears are running on sealed bearings, but the gears themselves will have one additional oiler (for the teeth) between them.  The original crank gear/basket gear is fed from a groove behind the thrust bearing (which is under the crank gear).  There will also be a small sump under the middle gear (lowest).  That's all the same method the original bike uses....should be good enough for my short runs.

Re: the clutch....I'll have the basket sleeved and the springs stout.  These clutches are pretty similar total disk area to some of the old 4-cylinder bikes (some identical part numbers); we put a lot of horsepower through those with the help of good springs (and that was on the dragstrip!). 

Most of all....I have to make it work with what's on hand and what I can modify.

Here's a couple pics showing my shaft retainers and the gear train with the back exposed.

JimL

[bak189]

Re. the clutch......you can always contact Barnett Tool and Eng. at 805-642-9435 talk to Mike and/or
Pat..............they are the M/C clutch specialists.......they have heavy duty springs......they have
special clutch plates, or they will make what you need........great people and they are into LSR.......

[beerbellykelly]

very interesting build-enjoying the fixes and the engine tech-great thread-keep at 'em!

[JimL]

Primary drive/gear train cover about done....a friend will TIG this for me.  The clutch release is working, and lined up perfect.  The bolt-on panel (diamond shape) gives access to the front crankshaft nut and oil pump/drive chain.  This will allow pre-pumping the oil system, before startup after long shut off periods.

More coming soon (picking up pistons, getting blocks bored, fiberglass about ready, chain drive adaptor shaft done tomorrow.....about to that point when there'll be a lot to do.

"The hurrieder I go, the behinder I get."....that's what mom used to say.

Regards, JimL

[JimL]

Comparison pic of original piston to new CP 13:1 with .020" overbore.  Original piston was 11.1 oz, new piston is 10.4 oz, and has shorter wrist pin.  You can really see the strange "22 degree twisted combustion chamber" design, in this photo.

A pic of the valve spring package (about 20lbs more base pressure), springs lighter and fewer winds than stock.

Blocks go for bore job, tomorrow.