T head engine by Brian

[aostling]

I will post one more video of this engine running, and then, as Bugs Bunny would have said--"That's all folks!!!" . . .

Running, and driving a load perhaps?

[brian Rupnow]

After painting and reassembling the engine, it looks lovely but it won't start. It won't start because it has lost compression at the valves.
It started and ran fine earlier this week. The painting process didn't involve any of the things that would make the valves leak. Valve timing and ignition timing have been checked, and they are "spot on". The only difference between this engine and other engines I have built is the exceptionally long guided area of the valve stems. I have a theory that the longer contact area is creating enough friction on the valve stem to keep them from closing properly. First and easiest thing to try will be stronger valve springs. If that doesn't fix things, then my other idea can be seen at the right hand valve in the drawing. The lower portion of the guide area of the valve cages would have a clearance from the valve stem, and an inserted, concentric supplementary guide Loctited into the very bottom. This may well be the reason that Vederstein couldn't get the valves to seal on the t head engine that he built.

[Sparky_NY]

Begs the question, if the engine ran fine with good compression before, why would the friction increase so much and compression lower with only a very few minutes run time? With running, the friction between the valve and guide would lower one would expect.

[brian Rupnow]

Sparky, sometimes I never know. When I first assembled the valves and guides, they worked and moved freely. When I first started the engine, I had to disassemble things, clean them up, and give a light regrind with 600 grit on the faces. Then the the engine ran quite well. Took some things off for painting, none of which had anything to do with the valves, reassembled things and it won't run, bad compression. None of my other engines have been like this, and the only difference is the length of the valve guides. If I was starting from scratch, I would grind the relief into the valve stems, not the guides. If I put stronger valve springs on it, I will see if there is enough valve to hang onto and use my toolpost grinder to knock about 0.015" off the stem diameter in the center where I show the clearance in my drawing.

[Sparky_NY]

Sparky, sometimes I never know. When I first assembled the valves and guides, they worked and moved freely. When I first started the engine, I had to disassemble things, clean them up, and give a light regrind with 600 grit on the faces. Then the the engine ran quite well. Took some things off for painting, none of which had anything to do with the valves, reassembled things and it won't run, bad compression. None of my other engines have been like this, and the only difference is the length of the valve guides. If I was starting from scratch, I would grind the relief into the valve stems, not the guides. If I put stronger valve springs on it, I will see if there is enough valve to hang onto and use my toolpost grinder to knock about 0.015" off the stem diameter in the center where I show the clearance in my drawing.

How about rechecking the valve timing? The cam(s) moved earlier in the build causing the same problem, that would be the first thing I would check, maybe they moved again.

Head gaskets have also been a problem area in the past, maybe haul out that air fitting and pressurize and check. Sealing that leaky spark plug wouldn't hurt either.

The valve train worked as is, the relapping the valves you did had nothing to do with the stems/guide clearance. From a engineering standpoint your proposed rework is a good idea but its already proven not necessary for a good runner. Something changed.

[brian Rupnow]

Sparky--everything has been rechecked since reassembling the engine.--valve timing, ignition timing, sparkplug sealing, head gasket, and seeing a visible spark with sparkplug laying out on the head.

[chipmaker4130]

How are those valve stems lubricated?

[Willy]

Can you hear from which valve the leak is coming from thru either the intake or exhaust port, if it is indeed a valve leaking?

[Sparky_NY]

Sparky--everything has been rechecked since reassembling the engine.--valve timing, ignition timing, sparkplug sealing, head gasket, and seeing a visible spark with sparkplug laying out on the head.

Dang, that should cover it. Still, something HAS to be different than when it was running well. It will be interesting to see what eventually gets it running again.

[brian Rupnow]

There is no provision for lubricating the stems except for squirted on oil and pre assembly oiling. The leak is mostly on the intake valve, but both valve cages and valves are identical, so I imagine there is some leaking at the exhaust valve as well.

[Sparky_NY]

There is no provision for lubricating the stems except for squirted on oil and pre assembly oiling. The leak is mostly on the intake valve, but both valve cages and valves are identical, so I imagine there is some leaking at the exhaust valve as well.

OOOO So there is a identified valve(s) leaking ! Seems I recall this happening on other engine builds, valves that sealed initially only needing to be re-lapped after a short amount of running.

What are the valve / seat materials again? Might be time to step back and reconsider the methods / materials in the valves/seats to determine why they are not holding up long. Too little a contact area perhaps? Just a guess.

In larger motors its fairly common practice to make the rocker contact a bit off center of the valve stem to promote the valve to rotate a bit in operation.

[brian Rupnow]

I'm pretty sure that the leaking is a result of the valve springs not being strong enough to firmly seat the valves. I have a "kit" with about a thousand springs in it, and I just grabbed a pair that were the right diameter. I suspect that there is enough friction between the valves and their long guides that the springs aren't doing their job. The valves were sealing well enough for the engine to run, as seen in the earlier video, and valves don't "go bad" in about a total of 15 minutes run time. The engine never got hot enough to do any valve burning. As I said, my first move here will be to try stronger valve springs. The current springs are only 0.026" diameter wire and are quite easily compressed.

[Sparky_NY]

You have done enough engines that if your gut instinct says the springs are too light then they probably are !

[aostling]

You have done enough engines that if your gut instinct says the springs are too light then they probably are !

Those two springs certainly do look weak -- this could be the solution.

[brian Rupnow]

I dipped into the Rupnow fortune today and bought a 10-24 Helicoil kit which comes with all the necessary drills, taps, etcetera and about 40 inserts in different lengths for $116.00. While I was picking up the kit, I picked up some very heavy, bull-doggy looking compression springs to be used as valve springs. The valve springs I have on the engine now are 0.026" diameter wire size. The new ones I bought are 0.049" wire size. They are also larger in overall diameter, so tomorrow I will machine new valve cups that go on the valves to center the springs. This business of valves sealing one day good enough for the engine to run, and then not sealing the next day is ridiculous.