Crankshaft experiment

Just some fun to show. Links, pics or movies.

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stew79
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Re: Crankshaft experiment

Postby stew79 » Wed Apr 25, 2018 8:51 am

yes jack, i did read that (and all of this very interesting project) but i am trying to think of a way around the "out of ratio" problem that becomes worse the faster it runs. swash plate fuel pumps can have an adjustable stroke which could be used to compensate at higher speeds ? perhaps the "proportional" approach to set the fueling, always has the same basic problem, but if you start from the top end and work down, it works well enough. (thats setting the max fueling first with way over the amount that you think the engine can burn, which must give a good safety margin as well) then reducing that max amount, so if the slower part, or initial pick up is just too rich. end result, top end strong, cool, safe, pick up to mid point a bit rich but the ignition is strong enough to cope.
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Re: Crankshaft experiment

Postby Jack Gifford » Thu Apr 26, 2018 5:24 am

You've stated the usual approach very well. If I had chosen parts of a "normal" nature (say a little Weiand 170 c.i. blower) I'd probably be well on my way to having it sorted out by now. But... this project is mostly about things I wanted to investigate (thread title: Crankshaft experiment). I really want to learn how much heating of the intake mixture can be avoided by turning a very large (511 c.i.) blower quite slowly. If my estimate of this blower's efficiency (using it in this manner) hadn't been so far off, there would not have been these setbacks to report.
Not quite apart yet- still hoping the repairs won't be too bad.
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Re: Crankshaft experiment

Postby minetymenace » Thu Apr 26, 2018 9:59 am

Jack Gifford wrote:I really want to learn how much heating of the intake mixture can be avoided by turning a very large (511 c.i.) blower quite slowly.

I would hope that most of the heating of the mixture could be predicted by Boyles Law, assuming an adiabatic process. If anything the, compression of the mixture will heat the blower more than the inefficiency of the blower causing the mixture temp to rise. As your small(ish) motor no doubt produces a lot of heat, I'm sure the blower is well insulated from the head. Do you measure the temperature and pressure either side of the blower?
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Re: Crankshaft experiment

Postby stew79 » Thu Apr 26, 2018 10:20 am

hi minety, as i see it there will be very little heat generated from the engine, and with so much fuel going through the blower with the air i doubt it goes over 50 deg c. i think methanol really is a wonder fuel and one day i will have a play myself.
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Re: Crankshaft experiment

Postby Jack Gifford » Fri Apr 27, 2018 7:00 am

Roots blowers are notorious for heating the mixture, well beyond the fundamental Boyle's law contribution. Most is due to fluid friction- mixture moving at high velocity through "leaks" (rotor-to-rotor, and rotor-to-case). Some is due to mechanical friction- Teflon strips under high centrifugal loading actually touching the case and other rotor. I've never measured temperature of my compressed mixture- just watched for symptoms, such as sensitivity to small increases in spark lead, signs of highly heated plug electrodes, etc. [For this to be the learning experience I intended, I'll probably eventually add a sensor for compressed mixture temperature]
Yes, vaporization of the methanol does accomplish much mixture cooling (my V8 would frost up the blower case when idling with no load). But this cooling is limited by the fact that my engine (and most others) put the majority of alcohol into individual port nozzles, just a couple of inches from the intake valves. This is done to allow adjustment of fuel/air ratio to individual cylinders- GMC-style Roots blowers tend to push more air to the front cylinders.
"Motley" bike history: Horex 400, 1940 HD 45 FH, HD Baja 100, '49 Indian Scout 440, Victor 441 Roadster, H*nda TL125, Guzzi V50, H*nda FT500, 400-4, '71 B50T
Aside from bikes: known as the "guru" of M/T hemi Pontiacs

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Re: Crankshaft experiment

Postby stew79 » Fri Apr 27, 2018 9:06 am

jack, i assumed the fuel was injected into the blower, not at the valves. i have often wondered about the small helix angle of the blower rotors, having an influence on local pressure, after all the type with the much greater angle are almost axial flow. the more i read and see the more i want to play
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Re: Crankshaft experiment

Postby Jack Gifford » Sat Apr 28, 2018 5:56 am

With head now off, damage assessment is a mixed bag. A small torched spot in the chamber of #3 by the exhaust valve appears quite repairable. But #2 & #3 sleeves are damaged. If they were typical cast iron sleeves, I wouldn't be too surprised that they appear to be cracked at the approximate spot their top rings sat when the detonation occurred. But I specifically turn my sleeves from DOM steel tubing, to not suffer the cracking that cast iron does when shock-loaded. So until I can get it completely torn down and those sleeves pressed out, I won't know exactly what the failure amounts to.
"Motley" bike history: Horex 400, 1940 HD 45 FH, HD Baja 100, '49 Indian Scout 440, Victor 441 Roadster, H*nda TL125, Guzzi V50, H*nda FT500, 400-4, '71 B50T
Aside from bikes: known as the "guru" of M/T hemi Pontiacs

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Re: Crankshaft experiment

Postby Jack Gifford » Tue May 08, 2018 4:15 am

Air pressure check of coolant jacket shows that integrity of sleeves is fine. What appeared to be damage is actually addition of metal to some places on sleeves' surfaces. I'm guessing the detonation "slammed" the top rings forcefully enough to deposit bits of ring material onto sleeve walls. I'm hoping that's good news- assuming the walls can be honed true again.
"Motley" bike history: Horex 400, 1940 HD 45 FH, HD Baja 100, '49 Indian Scout 440, Victor 441 Roadster, H*nda TL125, Guzzi V50, H*nda FT500, 400-4, '71 B50T
Aside from bikes: known as the "guru" of M/T hemi Pontiacs


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