TWM140 is beating me!

[cpurvis]

You might be making the erroneous assumption that because the carburetor is "new" and the engine displays the same symptoms, that the problem lies elsewhere.

You might be overlooking the possibility that the "new" carburetor has exactly the same problem as the old one--a clogged passageway or jet. Chinese carburetors are not known to have the best quality control.

 

[cpurvis]

It didn't come from a blown head gasket. Probably from the piston rings being worn.

 

[Paxman]

You might be making the erroneous assumption that because the carburetor is "new" and the engine displays the same symptoms, that the problem lies elsewhere.

You might be overlooking the possibility that the "new" carburetor has exactly the same problem as the old one--a clogged passageway or jet. Chinese carburetors are not known to have the best quality control.

Yes yes...but now I have these carbs and can not get a new original one, so the only way forward is to eliminate all other sources for the problem.

It didn't come from a blown head gasket. Probably from the piston rings being worn.

How can oil get to the bolts if the rings are worn? I should have mentioned that the oil is on the threads. I'll see if I can upload some pictures...

 

[Paxman]

Here are some of the bolts.




And this is how it looks under the head. There are signs of escaping gases on the muffler and on the yellow chassis.

 

[cpurvis]

There are only a few ways for oil to get in the combustion chamber of a flathead engine: Worn rings or cylinder, excessive blow-by being routed into the carburetor or through a worn out intake valve guide. There is no way a blown head gasket on a flathead engine is a source of oil. It does not seal off any source of oil from the combustion chamber. The threaded holes for the head bolts would have to extend into the crankcase itself to reach oil. It doesn't look to me like the head gasket was blown anyway.

None of this is keeping your engine from running. It may use oil and smoke, but it will still run if it has fuel (and air in the proper amount), compression, and ignition (at the proper time).

 

[tadawson]

Yes yes...but now I have these carbs and can not get a new original one, so the only way forward is to eliminate all other sources for the problem.



How can oil get to the bolts if the rings are worn? I should have mentioned that the oil is on the threads. I'll see if I can upload some pictures...

No, but you can easily rebuild your carb to like-new condition, eliminating the chance of bringing in defective castings, passages, etc. from an unknown source, which it looks like you did. The Chinese carb, as expected, accomplished nothing.

I had a similar case with an old Tec, and the fuel line was breaking down amd dropping finenparticles intonthe carb, clogging a jet. Letting it sit for a while would let the cycle repeat, as did cleaning the carb. The fix tonget it to keep running was a tank flush and new fuel line. On the oil, I've also had engines that had good compression, started on one pull consistently, and would fog the neighborhood. A hone and new rings had it back to zero oil use like new . . .

 

[jp1961]

https://youtu.be/iyyy-JE7cPg

 

[bertsmobile1]

The staining on the deck is heat from the muffler and the fact it is in lines is from the breeze created by the cooling fan.
It might just be a shadow but I see what looks like a crack between the inlet & exhaust.
As previously mentioned, nothing stops a flathead from running.
I run motorcycles dating back to 1917 most are flatheads and provided that the spark is happening at the right time they will run with all sorts of problem.
I have ridden 600 miles on an engine with a cardboard head gasket because the composite one crumbled and fell apart.
I had another that broke a chunk out and we had to start that by pushing because it lost so much compression at kick start speed it could not be started .
I rode that bike every day of a 6 day event, just had to stop on a hill.

On the subject of the bolts.
Screw then in till they bottom out then measure the space from the cylinder to the under side of the head
Now measure the depth of the hole through the head including the head gasket.
The head hole needs to be 2-3 full thread lengths longer than the free length of the bolts to enable proper clamping.
If this is not the case then either you have a build up in a blind hole or the bolts have stretched.

 

[Paxman]

It might just be a shadow but I see what looks like a crack between the inlet & exhaust.

I see what you mean...just checked, it's a shadow made by quite a bit of flash from the moulding.

On the subject of the bolts.
Screw then in till they bottom out then measure the space from the cylinder to the under side of the head
Now measure the depth of the hole through the head including the head gasket.
The head hole needs to be 2-3 full thread lengths longer than the free length of the bolts to enable proper clamping.
If this is not the case then either you have a build up in a blind hole or the bolts have stretched.

I will definitely check that!

https://youtu.be/iyyy-JE7cPg

Very informative video! I just checked the valves and they both felt pretty good when I spun them. I did spray some lubricant along the stems and it felt like they freed up a little more. However I found one thing that I don't know if it supposed to be or not. I rotated the flywheel one full revolution and paid close attention to how the valves moved. On the compression stroke the exhaust valve opens a tiny bit (0.4 mm, 1/64") during the first half on the stroke and then closes again at about 75% of the stroke. Is it supposed to do that? If not, what would cause it to? It's like there is a bump on the back side of the camshaft lobe for the exhaust. I have never seen that in an engine...

 

[jp1961]

Hello,

Yes, the engine has a built in decompression feature built into the cam inside the engine.

Try rotating the valves when they are open (as per the video), they should spin freely. Now that you have the head off, this should be really easy. Try a rust penetrating oil like WD40 or PB Blaster, because if the engine sat for a while the valve stems probably have corrosion on them.

When working on anything,,,YouTube is your best friend.

Now I'm thinking out loud, but I wonder if the decompression system is shutting off, once the engine catches? One step at a time I guess.

Regards

Jeff