Compression rate

[Steve Swan]

Back to the original problem: Your great running J was shut off one day and the next it won't start. I think you're barking up the wrong tree chasing compression ratios. These engines will run with very low compression! My reference is Brand X, Excelsior which is also an IOE design, similar to Harley. My first X project was a 19 X full electric model, engine previously worked over decades ago by one of the old timers in the club.. It was stock compression at 4.5/1 and had a battery ignition system, so guaranteed HOT spark at any RPM. There is also a compression release tied into the kick starter, lifting the intake valves for the first 1/4 stroke of the starter. I could literally start that motor with my hand, pushing down on the starter crank! At one point I pulled both intake cages out and redid the valves and guides, they were old originals, worn quite a bit. I re-installed them and started it up for a test ride. Started perfectly, super easy, but..... Going over 20 mph it just slogged along, could barely get out of it's own way! Looking closer, I discovered a MAJOR leak in the front intake cage / nut assembly. Like HD these are a bear to get sealed up properly and a source of constant concern, front especially. After I re-sealed that up and did a leak test, it started just as easy and then had POWER!

My point here is even a massive air leak will still allow the engine to start and run! As RPM goes up, then the air leaks quickly become a huge issue!

So, stop fretting about compression ratio, you have plenty!!! Interesting comments, science and math from all, but not necessary here! Look at the other two variables, fuel and spark! If you're running a magneto, pinch the spark plug gaps down to .015". This is contrary to what the book says but will make starting much easier! The reason here is the inherent weak spark from a mag at low RPM. If it has a small gap, the spark can jump that much easier at low RPM, making a good hot spark and you're off. Yes, it's fine to run them that way down the road. Fuel can be another issue too. I've discovered these motors are pretty particular about idle settings and need a rich setting to start easily. If you choke the motor, CLOSE the throttle and kick it over once or twice, there should be fuel dripping out of the carb intake. If not, fuel may be your issue. I've had this issue before, motor runs perfectly, shut it off, 15 minutes later, it will not start!!!! No fuel... perhaps the float stuck and all the fuel boiled out, fuel off, who knows? But, restarting the process would always get it going.

In 2018 I prepped the 24 Big Chief and sidecar for the Cannonball. It ran like a top, until..... I hauled it to Davenport. That thing was a BEAR to start! It was embarrassing to kick it 20 times with a crowd watching. They probably thought "this guy is an idiot, and he expects to do the Cannonball when it won't even start!!" Things got worse in Portland Maine.... Obviously the issue was no fuel, because of the change in altitude. I had richened the idle setting up a couple notches thinking that was enough. Once started, it ran perfectly and would idle smooth and slow. I called Howard Wagner and asked for his advice. He asked what my starting procedure was, I explained what I was doing. He chuckled and said, "Hmm, after all these years I have to explain to you how to start your motorcycle?" He explained the process I now use all the time: Full choke, throttle closed, 1-2 priming kicks. Choke half open, slight throttle, ignition on and kick, should take right off. It did!!! He explained to me something I never thought about: The idle and priming circuit works with the throttle CLOSED! This allows all the fuel to be pulled through the idle circuit, which (one way or another depending on carb model) is richened up by lifting the low speed needle. If the throttle is opened, even a little bit during the priming kicks, much less fuel is drawn in. Still, I opened the idle circuit up quite a bit to get it adjusted for altitude.

So, back to basics, you have compression, now insure you have fuel and spark. If you have all 3, it WILL go!

Gene, excellent points! Thanks for taking the conversation back to basics pulling up gas through the idle circuit richened up by lifting the low speed needle. Both my JD '27's start nearly every time 1st kick, throttle closed, 1/3 from full advance, but only after the routine of 2 priming kicks with ignition off is one of necessity. Hot starts, usually will start with throttle closed and rest of the time with throttle fully open; very rarely is a prime kick needed for a hot start.

These IoE engines are a sophisticated version of the hit-and-miss utility engines. I will again assert the importance of knowing there are no inlet leaks in the manifold tracts -and- also the inlet pockets are sealed as in no leaks confirmed by bubble testing. I also appreciate your comments on the affects that changes in altitude can have on starting characteristics. Wednesday past, i rode for the first time to 7,000 feet, stopped for a couple pics and was pleased that the engine started like it does at my home altitude of 5,200 feet. The carb on my bike is the Schebler model DLX38, specific to the '27 year-model JD.

[chuckthebeatertruck]

This thread perfectly encapsulates the differences between prewar bikes and later bikes.

It also exemplifies the saying: There is a difference between knowing the name of something and knowing something.

thanks for sharing

it’s good this one exists. Someone in the not so distant future will need it.

[duffeycycles]

I agree with Gene on closed throttle for priming,but HD service info always said open throttle for priming.I have seen issues on mag bikes,with some brands of spark plugs giving weaker spark than others when testing with a set of plugs installed,& test plugs grounded & not installed.Some gave good spark,some not.They all ran fine once started.

[T. Cotten]

I agree with Gene on closed throttle for priming,but HD service info always said open throttle for priming...

I suspect, Duffey,..

The open throttle prime was probably a hold-over habit from the HX days; The DLX (and later L&L) design draws from its idle circuit best when the disc is close to the idle bleeds.

....Cotten

[kitabel]

Yes, closed throttle restricts engine vacuum to the idle circuit.

[T. Cotten]

Yes, closed throttle restricts engine vacuum to the idle circuit.

Not exactly, Kitabel,..

We want enhanced vacuum at the bleeds.

Open throttle robs the Bernoulli draw upon the bleeds, drawing from the main nozzle instead, (if actually possible by just kicking, without choking), and would evacuate the idle gallery down to the bowlstem (if it did).

A nearly-closed throttle disc directs air over the bleeds (apparently into the big front hole, to mix, and then to suck out the small hole), providing a metered fuel emulsion instead of a burp of raw gas. Or so I read somewhere...

....Cotten
PS: The genius of Maldwyn Jones had my astonished disbelief decades before I knew his name.

[aumick10]

Cotton,
You mentioned a holdover from the HX days. Does this mean the starting procedure for a HX is different to that for a DLX? Mick

[T. Cotten]

Cotton,
You mentioned a holdover from the HX days. Does this mean the starting procedure for a HX is different to that for a DLX? Mick

Since I have pretty much only dealt with them on the bench, Mick,..

Starting procedure differences would be far-fetched conjuring on my part. But the HX throttledisc has no bleeds to deal with, so its basically either open or shut.

I'd opt for open.

....Cotten

[zig1]

Who sells the sealing ring /gasket that goes between the inlet housing and cylinder or the part number please ?Thanks

[Steve Swan]

Who sells the sealing ring /gasket that goes between the inlet housing and cylinder or the part number please ?Thanks

my first hand experience dealing with rust-pitted housing and cylinder seats, those rings don't seal... https://www.antiquebike.se/en/pruduc...intake-va.html

[T. Cotten]

I imagine its too hot for PEEK, Folks,...

A pyrometer reading from a running machine would be prudent.

But I'll cut some if anyone wants me to...

....Cotten

[Steve Swan]

I imagine its too hot for PEEK, Folks,...

A pyrometer reading from a running machine would be prudent.

But I'll cut some if anyone wants me to...

....Cotten

Tom, 3 items of note:

1. i just looked up melting temp for PEEK, 649.4F... i imagine there might be variances in melting temp's for different types of PEEK...? is 649.4F the temp you are familiar with? looking at attached Heat Chart, one could guess the seat temp might not come close to 649.4F...? The seat in the cylinder the inlet housing fits into is roughly just under 2" ABOVE the exhaust valve which is, of course, in the cylinder.

2. When i was battling my buddy's inlet housing leak, having confirmed the copper rings did not seal, he made up a set of rings in PEEK which also disappointingly did not seal...

3. So... Following the advice of a recognized JD engine builder (going against how i go about sealing an area like this), i put (and have been on all my J-type engine builds), i put a thin coat of Permatex Ultragrey on the flat "L-shaped"seating surface of the inlet housing -and- another thin layer of goo on the upper (-and- i know how you feel about using gasket goo) (flat) surface of the housing, then smeared the top goo layer against the adjacent wall of the cylinder, installed inlet lever assembly followed by tightening the large ring nuts. No leaks, over 100 miles on the job since that pivotal (for me) moment in time. Permatex Ultragrey spec sheets rear, "Typical Environmental Resistance" is -65F to +450F continuous, -65F to +500F intermittent. Melting point is unknown...

HEAT CHART.jpg

[T. Cotten]

I wouldn't think sealing would be a problem, Steve,...

Unless the mating surfaces are just too far gone. (Then its a re-machining issue.)

Otherwise, the problem is only to stay sealed.

That's the trick.

....Cotten

[Steve Swan]

I wouldn't think sealing would be a problem, Steve,...

Unless the mating surfaces are just too far gone. (Then its a re-machining issue.)

Otherwise, the problem is only to stay sealed.

That's the trick.

....Cotten

Indeed and agreed on all three, Tom! The seating surface area of the new housings is perfect. The seating area in the cylinder that the housing fits into is rust-pitted. Impossible to get a seal without machining the seating area in the cylinder. Will see how long the Permatex holds its seal...