1937 ULH starting problem

[Tommo]

Steve,
Here's a picture from Nicholson's that shows the timer position in relation to the flywheel timing mark.
Hope it helps

[kitabel]

The results are in: no one knows.

[Tommo]

Kitabel,
Is that sort of response really necessary.
See my new thread

[shinedogg]

Thank you Tommo, I really appreciate the expertise. invaluable. Everyone else included. Thank you.

Steve

[kitabel]

You mean the mistake you made, and attributed to Palmer? Read the corrections made on your post by others.
I can tell the difference between M-51 and M-5/55 internal parts, and between M-51 and M-5/55 float bowls in the dark.
Wow, how many hints do you need before you actually look at them?

[kitabel]

As to your actual starting problem: low cranking compression has an evil twin caused by the same factor - poor ring seal.
This means that the engine is unable to "trap" (seal) the volume in the cylinder when the intake valve closes, hence the low reading.
The engine is also not capable of sealing the rings in the opposite direction - when the decending piston applies vacuum to the carburetor. Low CCP = low starting vacuum.
Your problem may not be entirely this, but it doesn't help.
BTW: this (low intake vacuum) is also present in engines with excellent ring seal and low static CR. A 6:1 CR engine will have significantly less intake draw than the same engine with 9:1 CR.

[knucklehead 61]

could be a bad condenser. that would cause it not to start.

[shinedogg]

I'm going to deal with the compression issue first, it's not up to spec, so it needs to be fixed. I will let you know.
Thank you all for your responses, I will address each one if a top end job doesn't solve the problem.

Steve

[kitabel]

If you haven't taken the heads off, I suggest you try spraying some light oil (WD40, etc.) down the plug hole while kicking the engine through several times. This forms a very light hydraulic seal between the rings and cylinder wall and will significantly increase your CCP - IF rings are the problem.
If it doesn't improve, you may have another leak source, including a blown head gasket, damaged head bolt hole, bad valve seat. These are not likely because they generally don't affect both cylinders to the same degree and at the same time.
Mis-timed intake cams (leaving the valve open too late ABDC) would also do this, but not relevant in your case.

The approximation given earlier of atmospheric pressure × static compression ratio is fairly accurate but may be a bit conservative in engines with very mild cam timing (all early flatheads, exception: K/KH) in which somewhere between 15 and 20 × CR will be closer. As the intake valve closing is delayed by hotter cams (Sportster), the trapped pressure goes down.

[shinedogg]

Thanks for the info. Kitabel, I have suspected the rings as kicking her over is way too easy. The light oil trick improved the compression by 5. Now that I have accurate feedback on compression ratio the top end is coming off.

[kitabel]

I would expect more improvement than that if ring seal is the only problem.
Curious: has the engine ever started well? Apart for any reason? Prior rebuild?
Have you seen the pistons @ TDC flush (or very close) to the deck?

[shinedogg]

No, first time starting her. I have seen the tops of the pistons flush. I have a new top end from American Cycle Fab. I just got your books on 80 performance and oiling system. It's cold outside right now in Alaska, so good time to do this. Looks like the valve seats have been cut so many times that adjusting them is kinda tricky, measure at the bottom and adjust at the top of the cam, so here I go....

[Rubone]

measure at the bottom and adjust at the top of the cam, so here I go....

Not sure what you mean by that. Valve adjustment is the same unless they are so deep as to lose all free play in the tappet screw range. Always on the lowest point of the cams.

[shinedogg]

Robbie, what I meant is the tappet adjustment nuts are so low in the blocks that I have to bend my feeler gauges at a 90 when I'm off the lobe, measure, and turn the adjuster and lock nut at the top of the cam lift, cuz I cant turn the tappet adjuster or nut when it is that low inside the blocks. took awhile to figure out that was the trick to adjustment with valves so low in the seats.

[kitabel]

This is a sign of many valve jobs, valve seat recession etc. which has moved the valves down into the seat bowl, and the stems extend farther down, "using up" the adjustment area. You could just shorten the stem ends, but both the breathing and temperature of the cylinders is harmed by the seat condition.
This should go on the list of things to do when servicing the cylinders. Frankly, if the top end was recently done this is not professional quality work. Installing seat inserts is, IMHO, not a reliable method for many reasons. The most practical cure is, in order:
1. bore & hone the cylinders to whatever size you need to restore the wall.
2. assemble the pistons on the rods (no snap rings needed) and install the cylinders.
3. measure the deck clearance, you want .035-.040" @ TDC including the base and head gasket compressed thickness.
4. yours is probably considerably more than that, like .060" or more.
5. mill the cylinder's deck surfaces to get the correct distance.
6. this will expose fresh metal, and also remove the highest (worn) part of the original valve seats.
7. this may be enough that a fresh seat is higher than what you have now, pulling the stems up off the adjusters.
8. if not enough, shorten the valve stem (I would use lash caps, or Harden-It to re-harden the ends).
9. last resort: replace the valves with 1/8" oversize head (Eastern etc.) which will seat higher, but only use as much diameter as you need. If +1/16" is enough for a fresh seat, reduce the valve head to that.
10. prepare valves: 45° seat, 30° back cut to narrow the seat to .125" (intake), .156" (exhaust), add a 15° inside that if possible (may not be enough metal). No sharp marks near the stem-to-head radius!
11. prepare cylinder: 45° seats same width, narrow from inside with 60° cutter. If the highest edge of the new seat is below the deck surface, relieve this from the top with a 15° cutter to just intersect the top of the new seat.