T head engine by Brian

[brian Rupnow]

Simple answer--I don't know. The carb could be tuned a bit rich.

[Sparky_NY]

I noticed a interesting observation in your video. Watching the exhaust, its clearly visible that it is mostly clear then there are occasional "puffs" of smoke, the cycle repeats. I am wondering what is causing that strange exhaust behavior, ignition misfire, fuel building up somewhere?

[brian Rupnow]

This is the T head engine I designed and built a few months ago. I finished the engine, tuned it to run and took a video. Then it went up on the shelf. Yesterday I had some free time, so I got it off the shelf, down to my work area, and made up a spring return bracket and a throttle extension handle with a return spring. I started it up, adjusted the idle, and then let the engine run until it ran out of fuel. I had my office door open while this was happening so I didn't gas myself. Actually, I went into my machine shop and worked on something else until I heard the engine quit.

https://www.youtube.com/watch?v=X71y1TEn3FM

[The Artful Bodger]

Thanks Brian, another successful project enjoyed by us all!

[brian Rupnow]

Matt--You're right. Every new engine presents me with more opportunities to learn.---Brian

[mattthemuppet]

great work Brian, I love seeing the problem solving you do to get these running. I guess there's something to learn with each build!

[brian Rupnow]

So this is it kiddies. The engine is completely finished, runs the way I like, and looks pretty too. I had a few problems with valves not sealing, but new valve cages were made and the problem was fixed. This has been an interesting engine to build, and it is similar in many respects to the flathead engine I built ten years ago. Complete plan sets are waiting to be sent out to anyone wishing to build this engine.($25 Canadian funds), contact me. Thanks to all who have followed and commented on the forums as this engine came together.---Brian Rupnow

https://www.youtube.com/watch?v=YvneRKPC0yM

[brian Rupnow]

Sparky---A combination thereof. The compression was very very low. Low to the point where the engine wouldn't fire. The second set of valve cages fixed the compression issue, but there was still friction between the gears and the aluminum gear guards. Engine would fire and run along with the drill I use as a starter, but not take off and run on it's own. I blued the inside of the guards with layout dye, then bolted them in place, tried to start the motor, then took the guards off and sure enough, the rub marks stood out against the bluing. A bit of work with my Dremel tool to grind the rub marked areas to clear them and the engine took off and ran like a racehorse. After running ten minutes to seat the valves, engine now has very good compression.

[Sparky_NY]

So it was things rubbing and not the valves? From your description is sounds like it wouldn't run with just the new valve job.

[brian Rupnow]

It's been a wild and crazy two weeks since I first had this engine running. I have been very busy changing my shop around to make room for a big DoAll Bandsaw and preparing to sell my smaller metal cutting bandsaw. Strangest thing---the engine ran fine before I painted the flywheels and gas tank, but after the paintjob I couldn't get this thing to run for love nor money. These engines are not terribly powerful, and I was having enough interferance between the large timing gears and the aluminum casings over them to keep the engine from running on it's own. The engine ran again on it's own for the second time about 3:00 this afternoon, and I've been chasing down interferences and tight spots until about 20 minutes ago. The small carburetors from Traxxas are just right for these engines I build, but the throttle is very loose so that it can be operated by a servo. I don't use servos to control my engines, and the default setting is for the carburetor to open the throttle wide open just from engine vibration if I don't have something connected to that throttle. Tomorrow I will post a better video out in my main garage where there is lots of natural light with the garage doors open, and I have a better hook up for the engine throttle.---And yes, that little 10 blade fan being ran from the flywheel by a rubber o-ring puts out an amazing amount of air over the cylinder.---Brian

https://www.youtube.com/watch?v=wPkiDVyb26s

[aostling]

Now that you have the valves out you can inspect them with a high-power loupe to see if there are any brass rubbing marks on the steel. That would indicate galling, an explanation of why the engine ran nicely once, and then gave up the ghost.

A 50mm SLR lens makes an excellent 20-diopter loupe, if you have one somewhere around the house.

[brian Rupnow]

So, here is a family picture. The cylinder head with new valve cages pressed and loctited in place, the old valve cages which have been pressed out (You can see the excessively large valve seat area in the picture), along with valves, keepers, and springs. I haven't used my special tool for cutting new valve seats into the cages yet, I'll wait until the Loctite dries 24 hours. I am now using my wifes old digital camera, as it takes pictures much more clearly than mine. Design review came back to my customer today on the welding fixtures I designed, and it looks like I will have a full day tomorrow just making all the changes.

[Willy]

yes, exactly what i'm suggesting, smaller contact area on the seat.
Brian in prior projects is pretty good at lapping parts together, so I propose this:
Make 2 dummy valves with a turning shank projecting above the head. these are your laps. Each one is slightly different seat angle from actual valve. one is a plus angle the other is a minus angle.
One or two degrees of difference may lap quite fast and be good enough.
in use you do not 'cut' a 3 angle seat, but rather use the baddest coarsest grinding compound, and lap away enough material such that the end result is smaller contact area for the real seal.
Combustion firing pressure is what really closes the valves solidly. The valve springs/seats have to be good enough get the combustion process started.

Good approach to zeroing in on a more precise valve and seat interface.

Another technique often used is to cut the seat at a 45° angle while cutting the valve's face at a 44.5° angle.

[Ringo]

Three angle valve grinds are used on most production M/C, automotive, industrial, etc.engines that I have service manuals for, some dating back to the '30s.
In reality it is the only way to narrow the contact patch for good sealing and to center it.

However I can certainly sympathize with Brian's plight in doing so on an almost microscopic level.
All I can suggest is to keep the lapped contact area small in order to increase unit pressure in that critical area.

yes, exactly what i'm suggesting, smaller contact area on the seat.
Brian in prior projects is pretty good at lapping parts together, so I propose this:
Make 2 dummy valves with a turning shank projecting above the head. these are your laps. Each one is slightly different seat angle from actual valve. one is a plus angle the other is a minus angle.
One or two degrees of difference may lap quite fast and be good enough.
in use you do not 'cut' a 3 angle seat, but rather use the baddest coarsest grinding compound, and lap away enough material such that the end result is smaller contact area for the real seal.
Combustion firing pressure is what really closes the valves solidly. The valve springs/seats have to be good enough get the combustion process started.

[brian Rupnow]

I spent all of yesterday flogging a dead horse. Today I am going to make new valve cages and loctite them into the head. A close visual inspection of the existing valve cages shows that the seat area has become too large because of repetitive lapping to get a good seal on the valves. Also, due too the method I used when making them, the seat area is not perfectly centered on the guide area. I tried to take picture to post here, but my digital camera can't get a shot which shows it clearly.