BSA B50 -500 APG Build

[Koncretekid]

I forgot to mention that the flow number for the head are up to 135CFM at 10" of water pressure.  New intake valves (titanium) are shown below. Exhaust port and new JE piston are shown as well.

[wobblywalrus]

It is looking good.  What were the flow rates at 10" head with the standard valves and ports?

[Koncretekid]

Wobbly,
According to Ed V., flow rate for stock head is around 85CFM.  I have a "poor man's" flow bench as seen below, but numbers aren't really comparable.  Unfortunately, I had only 24 hours before I had to leave for N.S., so I didn't get to make any improvements.

My flow bench is a flow velocity measuring device which is inserted into a 4" PVC pipe.  Static pressure is measured using a manometer, and flow is provided by a shop vac.  The shop vac will only provide up to 5" of water static, so my numbers are only comparable to my measurements.  The two valves below the bench are to adjust static pressure, after changing the valve opening.  The flow measuring device is supposed to be accurate to 2% at 3 significant figures, and seems to give a good steady reading. It is good for measuring changes to the flow, just not comparable to other flow bench numbers.
Tom

[wobblywalrus]

That is a big improvement.  The problem is knowing when to stop.   

[Koncretekid]

INTERLUDE:  Back home in Nova Scotia now, and what a circus.  Yesterday evening the loons were calling each other in their traditional Spring Mating Ritual -- If I hear it again this evening, I'm going to stick my movie camera out the back door to record.  Then there was a ruckus in the dog's barn (that she doesn't actually sleep in!).  So I put on my shoes, opened the door, and out we came -- dog going at one side of the mini-barn, cat going the other, and I with my trusty mag-lite in the middle.  I arrived at the scene just as the cat and the dog collided as they circled into each other.  We treed the varmit -- a big bushy raccoon.  I later thought that I was glad it wasn't a bear -- armed only as I was with a lame 11 year old mutt, a cat, and a flashlight.  Today there are seagulls and cormorants diving in front of the house, for the Spring migration of kiack (gaspereau)  that  swim up into the lakes to spawn.  You had to be here.  Off topic, I know, but sometimes you just have to take a break.

That is a big improvement.  The problem is knowing when to stop.   

Wobbly, you're right.  And without a Dyno run, who knows.  All I know is that with the new motor (92mm x 75mm stroke) vs the old motor (84mm x 90mm stroke), and with 1500 more RPM, I didn't improve in 2010 over 2009. So I'm guessing that in spite of the extra Revs, the motor just couldn't inhale any more mixture.  With this new head, along with 2mm bigger carb (flat slide, at that), and a shorter exhaust, I hope to have the right combination.  Unlike drag racing, we can't make a single change every 2 weeks and go back to the track, so it'll have to be all or nothing.  So here is a photo of the new intake port vs. the stock one.  What do you think?

Tom

[Koncretekid]

Back to the topic.  I had to completely disassemble the cases because the new cam wouldn't fit the bushing in the right crankcase.  I've got a few parts here to put back together here.  Thank God it's only a single!  Photos show the cam in the outer case, ok, but the bushing in the inner case is the culprit.  It's about .0005" too small.  I'm hoping to catch a machinist after lunch to ream it out.  The last photo is the "trick" pinion gear that drives the cam next to the stock one.  Five choices of cam timing.  Unfortunately, it takes at least an hour to make a change, so I hope I get it right the first time.  All I can do is make a choice, check it with degree wheel and dial indicator, and give it a try.  Won't know which is best without a dyno run, none of which are planned.

[wobblywalrus]

Tom, I was hoping you knew when enough is enough with porting.  I do not.  In the past I overdid it and made them too big.  The bike ran better before I ground on the head.

[Koncretekid]

I disassembled (split) the cases and removed the con rod to inspect the bearings.  These bearings have only 7 runs on them, but better to be safe than sorry.  Crank journal and bearings look ok to use again.  While I had the cases apart, I added a scraper closer to the crankshaft, because the flywheels are smaller in diameter than the originals.

[Koncretekid]

After re-assembling motor, I had to dial in the new cam with the multi-position crank pinion.  I tried 6 different permutations before I got it where I wanted.  Ed Valiket told me the easy way - dial it in with just one pushrod in place before the head in bolted on, then find the centerline of the lobe and subtract the opening number.

[Koncretekid]

I clayed the head and cc'd the combustion chamber while I was at it.  The clearances are seen in the second photo, and are a bit excessive, if anything.  About .070" to .110" at the valves.  I could easily mill the head or the top of the cylinders, but I think I will leave it for this year.  compression ratio works out to about 11.7 to 1.

[wobblywalrus]

Tom, why did you put in the oil scraper?  How does it help?

[Koncretekid]

Wobbly,
If you look closely at my photo, you'll notice that the original B50 cases (1971 vintage) had oil scrapers built into the crankcase halves.  The theory is that oil clinging onto the flywheels causes drag.  In my motor, the flywheels are actually from a 250 cc motor and are smaller in diameter than the 500cc flywheels.  Hence the original scrapers did not function.  Here's hoping that BSA, Bill Jenkins, and others sources that I have read are correct!
Tom

[saltwheels262]

Wobbly,
If you look closely at my photo, you'll notice that the original B50 cases (1971 vintage) had oil scrapers built into the crankcase halves.  The theory is that oil clinging onto the flywheels causes drag.  In my motor, the flywheels are actually from a 250 cc motor and are smaller in diameter than the 500cc flywheels.  Hence the original scrapers did not function.  Here's hoping that BSA, Bill Jenkins, and others sources that I have read are correct!
Tom

harley crankcases are the same way. when smaller than stock diameter flywheels
are used, the scraper plate is built up by welding  or the way that you did it.

franey

I believe car engines can have scraper plates installed for the cranks.

[wobblywalrus]

Thanks for explaining this.

[Koncretekid]

The original rotor had had the center pressed out to use as a spacer without the rotating mass.  I'm pretty sure that the rotating mass would not have been detrimental at Bonneville, but it had already been done.  But without the rotor, there are no timing marks.  I machined  a large washer, and welded it to the old hex center piece.  Then, by using a dial indicator and a degree wheel, I made a table of crank degrees vs. indicated distance before TDC.  I then marked the new washer with TDC, 26, 30, and 34 degrees.  At least I now will have some indication of timing.