Perplexed

[King]

Hi All

My 51 FL had become impossible to kick start and when I finally got it running (downhill start) it ran on only one cylinder. A quick check of the plugs showed the rear cylinder to be oil fouled. So I tore it down and discovered a blown rear head gasket. Yesterday I and a few of the bros got together and replaced the gasket and gave the bike a good check-up, timing, valves, manifold leak check, etc. It started on the second kick and ran well enough to determine that we were close on the tune-up items.

But try as we might it would not restart. The strange thing was that after about 4 kicks it became nearly impossible to kick it through. It took jumping on it with +200 lbs of lard to get the kicker to move.

I took it home, same kick through problem, so I and ran it downhill to start. It started but ran poorly, backfiring out the carb, and had barely enough power to get back uphill and into the shop. When I shut it down a fair amount of oil drained out of the primary even though it had been run for less than a couple of minutes.

Anybody had the same problem or an idea on what could be causing this???
The bike has about 230 hrs. on it since last rebuild, stock heads (rebuilt this winter) and Linkert carb (also fresh rebuild with Cotten’s Float). It ran great when I first got it back together this spring.

King

[Cotten]

King!

The culprit for almost all 'catastrophic failures" is not the hardware itself, but a source of unusual heat.

And the culprit may have a legacy even after a fresh re-assembly.
If a headgasket has "blown", it is almost invariably the result of heat, which causes the head casting to warp, particularly beneath the ports, and the headbolt inserts can protrude.

Were the headgasket surfaces re-dressed to as flat as possible? (It may still be sucking air at the gasket.)

And I must ask of course: you are are not using a tirepump, but a regulated constant air supply for the bubbletest, right?
You can turn the motor to open the intake valve and apply much more pressure to test the headgasket in the same manner.

Good luck!

....Cotten

[King]

Hi Cotten

The headgasket failure was from insufficient torquing. It appeared to have "failed" around one of the oil passages thus the oil in the cylinder/fouled ploug. We examined the parts carefully and no warping or extruded head bolt inserts were present and the whole assembly did not show any signs of over heating.

I'm doing the test with one of Mikes kits attached to a shop air line so it should be good.

I dont think the hard kicking and the head gasket were linked. When the kicking problem occurs it's almost as if one were trying to compress a clyinder full of water. Also the copius oil leakage is a major concern. I'm thinking some problem with the oil pump or circulation but what??

King

[steve_wood]

Did you try re-checking the lifter adjustment? Maybe they got out of whack somehow and affected the compresion.

[FlatHeadSix]

King,
I think Steve just gave you the answer, your problem is in the valve train. If you still have the original hydraulic (oil can) push rods they will cause exactly what you have described, the little hydraulic units colapse and the valves will not open, compression builds up in the cylinders and you can't kick it over even when jumping on the pedal with both feet. If you have solid push rods then they may just need adjustment.

mike

[King]

Thanks Guys

I will check the lifters (I have soilds, canned the oilcans years ago) and let you know the results. Screwed up valves would also explain the backfiring out the carb.

King

[fourthgear]

Or bent push rod (s)