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Still trying to figure out what is happening in the UL motor

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panic

Post Mon Jun 12, 2006 8:06 am

Never mind, no one reads it anyway.
Last edited by panic on Wed Jun 14, 2006 6:16 am, edited 1 time in total.
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thefrenchowl

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Post Mon Jun 12, 2006 1:32 pm

Hi all,

Panic
bore to stroke ratio - small bore makes for higher CR because the width across the chamber is smaller.


Quite right and probably why the KH is so much better than the K. The increase in power and torque is much more than the result of capacity increase done by just stroking it...

I've had the opportunuity to have both a KK for 6 years (now gone...) and a KHK (20 years now) and it's really night and day although the KK was no slush in any case (I use to take pleasure in humiliating Evo Sporty riders with it...) But that KHK is as good as any 60's Sporty, with quite a better power curve, feels more like constant pulling power, not hitting the cam at certain revs like most OHV set ups.

To come back to the CRs... On paper, there's nothing to say you couldn't get a flatty with 10 to 1 ratio, it's just the engineering side of it that would require (as the Panic quote implies) such high ratio between bore and stroke. There's a guy in Alaska that built a 5" KH in the past few years but one gets to pistons speeds that don't allow much tolerances and life expectancy.

In the end, most manufacturers doing flatties found that, around the 6.5 to 1 figure, they had a good compromise between usable power and not too much heat generated.

One mustn't forget that a flatty is as good as a DOHC in tech terms if not better: low inertia, valves can't hit each other, neither the pistons, hence you can use any amount of very fast convex ramps to open them if you don't care too much about the noise they generate as in racing and then gain maximum valve openings durations than an OHC or OHV can only dream of...

Still, heat is not the direct problem, it's more to do with the seats offset and the distortions that go with it, plus you are more or less obliged to have at the very least cast iron cylinders...

Dinner's ready, see you soon!!!

Patrick
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Cotten

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Post Mon Jun 12, 2006 8:12 pm

Panic!

I am having difficulty: How does one atmosphere get compressed to one-sixth its volume to produce the pressure of eight....At kicking speeds?

I appreciate your patience,
.....Cotten
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panic

Post Mon Jun 12, 2006 9:02 pm

Last edited by panic on Wed Jun 14, 2006 6:16 am, edited 1 time in total.
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100incscoot

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Post Mon Jun 12, 2006 9:35 pm

very deep panic

quote
The usual cam functions (also known as valve events) are Intake Opening Point, Intake Closing Point, Exhaust Opening Point, Exhaust Closing Point, Overlap, Lobe Separation Angle, and Valve Lift. The only one which affects cylinder pressure directly is the Intake Closing Point
end quote

does not overlap also effect cyl pressure if its major overlap thats opening the ex side while still under burn?
just a simple question for me to understand better
thanx for the in depth info
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Cotten

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Post Tue Jun 13, 2006 5:30 am

Panic!

If I understand your treatise (of course the math goes over my head...), then to get 120 psi gauge readings at normal compression, Jim had to be testing a hot motor and kicking at idle speeds.

Otherwise....your treatise seems to confirm that such a gauge reading indicates a rad ratio.

...Cotten
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panic

Post Tue Jun 13, 2006 6:48 am

Last edited by panic on Wed Jun 14, 2006 6:16 am, edited 1 time in total.
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100incscoot

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Post Tue Jun 13, 2006 7:12 am

i guess the writing is so deep i got a brain fart for a min there

a lot of mechanics dont realize you dont get the correct gauge reading with the throttle closed
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panic

Post Tue Jun 13, 2006 2:31 pm

Last edited by panic on Wed Jun 14, 2006 6:17 am, edited 2 times in total.
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thefrenchowl

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Post Tue Jun 13, 2006 2:47 pm

Cotten:
I am having difficulty: How does one atmosphere get compressed to one-sixth its volume to produce the pressure of eight...


You're right in thinking 6 in 1 should give a pressure of 6 BUT as you rapidly compresse air, its temperature rises dramaticaly and you get the whammy effect of pressure plus temp which makes the pressure rise even more... Classic example is your tyres, always check their pressure when cold. When they're hot, it goes way above cold figures...

Patrick
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WZ507

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Post Tue Jun 13, 2006 10:25 pm

There is a useful compression calculator at the following link that allows one to estimate both static and dynamic compression ratios if you know the particulars for your engine. Thought you may find it useful.

http://www.kb-silvolite.com/calc.php

On the subject of compression ratio, I have a few questions. I wonder if we might be mixing apples and oranges when we look to what KR’s ran (6.13:1 according to the Jerry Branch CycleWorld article), and extrapolate from this to what might be tolerable on the street. Rightly or wrongly I’ve always assumed that the low KR compression ratio was a necessity to keep the engine from melting down. Think about what someone would do to a poor KR on The Springfield Mile. Probably a 45+ second lap time, with WOT applied for maybe 12-15 seconds, then a short break for corner entry and right back on it for another 12-15 seconds. 12 seconds sounds like nothing, but in my mind it’s more like an eternity especially when you do it back to back 50 times in a row (25 lap race). So, in light of this example I fully appreciate how low compression ratio on a KR was mandatory for survival, but wonder if a street bike (like Jim’s?) that is used mostly for cruising under much milder conditions (dramatically lower EX temp) couldn’t employ more than 6.5:1 CR.

I haven’t seen anything from DumbClutch posted here for a while but on many occasions in past posts he seemed pretty proud of one of his rides that he claimed had ~ 8:1 CR, was very reliable, and would cruise at highway speed all day. Anybody using much more than 6.5:1, or does experience tell us you can’t go there, even for street use (where we pull it out one time, not 50 times in a row back to back)?

To shift gears to an earlier topic of this thread, I have a question for Patrick or anyone else that wants to chime in. The subject being “sparkplug location” that arose from Patricks quote -

“but don't forget that's with well cleaned up aluminum head contours, with nice straight shelf, slightly recessed but not hidden spark plug locations, piston slight pop up, etc”.

On many vintage flathead performance engines I note that the plug is in a recess. Often times this is solely to allow easy plug access, yet in other instances it is clearly by design, e.g., the head might be tapped for a 3/4” reach plug yet the factory plug will be the next reach short of that. What benefit does slightly hiding or recessing the plug serve in terms of combustion efficiency/inefficiency or heat management in flathead engines? In many hi perf OHV applications that I am aware of the plug thread is generally flush with the combustion chamber, hence my question about recessed plugs for flatheads. In some flathead applications I know of, the plug is actually designed to sit back in a hole (totally recessed), which seems absolutely backwards to me, but then again what do I know?
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Cotten

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Post Wed Jun 14, 2006 4:49 am

Patrick wrote:
"You're right in thinking 6 in 1 should give a pressure of 6 BUT as you rapidly compresse air, its temperature rises dramaticaly and you get the whammy effect of pressure plus temp which makes the pressure rise even more... Classic example is your tyres, always check their pressure when cold. When they're hot, it goes way above cold figures... "

That's what brings me back to my contention that 120 psi on a cold, kicked test is a high result for a Flatty.

Panic's treatis addresses dynamic and heated conditions, and the calculated pressures of a running motor. Commonly gauge tests are done cold on our machines, "cranked" only with the foot.

Most us would be hard pressed to kick faster than the simple conditions of basic Boyle's Law. A 74 incher at 6.5:1 would produce ~95 psi with zero overlap. Any overlap would reduce the gauge reading.

If Jim's CR isn't unusually high, then he's an unusual athlete!


...Cotten
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panic

Post Wed Jun 14, 2006 6:15 am

Sorry, too much trouble to read the correct answer?
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René

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Joined: Tue Nov 22, 2005 6:43 am

Post Wed Jun 14, 2006 8:58 am

JIm,
I guess this is more an answer to your "flywheel scraper" thread, but anyway;
The flywheel scrapers add oil to the oil mist, and oil mist is the only lubrication for the cylinder walls.
Removing or reducing the scrapers is not a very good idea.
The idea that Harley had to reduce oil because of poor oil rings is nonsense, because they had been using fully vented oil rings since 1940. They were only installed on slow vehicles like the Servi-car and City Police OHV's, other bikes needed all the oil they could get and were delivered with less effective (some say crummy) oil rings or no oil rings at all (UL front piston).
René
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100incscoot

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Post Wed Jun 14, 2006 11:46 pm

now look panic gathered up all his toys and ran home saying nobody gets to play with them anymore
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Graybeard

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Post Thu Jun 15, 2006 5:25 am

Panic, with all due respect I sure wish you wouldn't do that. Whether or not you're 100% right or 100% wrong or somewhere in between, by deleting your posts it makes it damn difficult for those of us who don't know 1/100th of what you do to learn anything. Many times I have to go back and reread posts in order to fully grasp the concepts being presented. This thread was one. Now with your posts deleted I can no longer follow it. The same thing has occurred on other subjects when your posts were deleted before I even had a chance to read them. I for one very much want to read your input on any subject matter presented in these forums. Your statement that "no one reads these anyway" is simply just not true.

Maybe you are just a cranky old bastard with no patience for those that you perceive to know less than you. I would prefer to believe that that is not the case. You have too much to offer. Again - with all due respect- a tolerant attitude rather than such a childish one would go a long ways.

Having said that I would also like to state that I respect and appreciate ALL info and opinions from ALL posters. Even that old? - young?- ugly?- 100incscoot. ( Now that's a REAL opinionated character!!!) :D :D :D
Aries51 (AKA Graybeard)
ROB in AZ

"Get on your bad motor scooter and ride"-Sammy Hagar
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HonestJohn

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Location: Dorothy, NJ. USA

Post Thu Jun 15, 2006 7:21 am

with respect

I don't think that any of us still alive can reproduce the conditions that the TRULY OLD FARTS from the teens,20s and 30s road these flatties thru daily, year in and out, thru deserts, rivers, mountains and considered railroad tracks THE SMOOTH WAY! My back is shot from a little teenage playin on a hardtail pan and I thought I was a tough SOB. Hell I couldn't keep up with a 60+ year old man on a 58 duoglide hand shiftin thru traffic. He, my great uncle, wouldnt ride with me anymore because I was too slow. That hurt. Now I'm the old fart laughin at the kids. I got nothin but respect for all who work on machines that go fast, blow up, fix em, go fast agin. It's hard enough for me just to keep mine runnin with this piss they call gas these days. Lookin for a point? Keep lookin.....
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barry

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Location: wooster oh usa

Post Thu Jun 15, 2006 7:25 am

imho... one thing about piston clearance to consider.. if you're running cast pistons they can be set up a little tighter as they do not "grow" like fordged pistons. forged pistons' crowns are a lot smaller than the skirt and have more cam grind.. as they heat up they grow to conform to the cylinder. thus.. the fordged pistons are noisy upon start-up until they warm up. on a relieved cylinder you're going to have scuffing on the valve side of the skirt due to the "washing" of the exposed side of the piston crown. the combustion temp of a flattie is tremendous...that's the main reason you can't run lots of compression like an overhead valve engine or liquid cooled engine.. the thermal efficiency is poor on gasoline. on alky it's another story as the alky burns much cooler.. tho you have to set the fuel system up much differently as the flow rate of alky is roughy six times that of pump gas. hence.. 5 hp briggs engines making 15 horse on alky go carts. i have always believed in a little top end lube in the race bikes..a little shop of marvel has made the pistons last much longer for us...
barry
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panic

Post Thu Jun 15, 2006 7:36 am

When a question is asked, I'm quite pleased to find that an answer has already been posted. I have no interest whatever in demonstrating my own ability, or arguing whether the earth is flat. There are 2 excellent reasons why you will not see a response from me:
1. the question has already been answered.
2. I don't know the answer.
Perhaps some of you would be well advised to follow that rule?
However, when the same tired subject is raised, repeatedly, and where the answer is well known, and still misunderstood, misconstrued, misinterpreted, despite the author of the post in question purportedly have already read my very accurate, complete and intensive explanation, I have no patience for either re-inventing the wheel or permitting the correct answer (mine) from remaining in the thread as is it were merely one of the many possible answers.
Why do you insist on discussing these matters when you ignore the answer?
To some of you the questions are not matters of physics or logic but of taste where everyone's answer has equal value. Let me illustrate:
Q: how many quarters do I get for a dollar?
I then see the answer posted as follows:
1. 2
2. 5
3. 11.58
4. 15%
5. only on Tuesday
I then post the only possible answer, and either get back such gems as "I was told that...", "in the real world...", and "the famous old-time mechanic always did this...", or I can just watch helplessly as people see not only my answer but the previous answers and continue to post nonsense.
By suggesting that my purpose here is to amuse you, and that my control of my own posts is "childish" (whereas criticizing me is not), you convince me that this is a waste of my time.
Please: which of you here has spent as much of their own time and money making this information available at no cost? I have over 100 separate web pages devoted entirely to enlightening the public on these matters, and you're proving to me that this time has been wasted.
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100incscoot

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Post Thu Jun 15, 2006 7:37 am

Even that old? - young?- ugly?- 100incscoot. ( Now that's a REAL opinionated character!!!)


HHHMMMM
seems that was a pretty opinionated statement for not knowing shit about the suject
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