Webster Build

[simister]

Jens,

Yes, I can move the spray bar higher. I will now change it to mid position.

John

 

[Cogsy]

You could try lapping the valve into it's seat with some toothpaste as abrasive. Do it by hand and only rotate the valve backwards and forwards (don't spin it) for a while, then change it say 90-120 degrees and do it again. A few minutes repeating this procedure is all that's needed to achieve a reasonable seal in most cases. Pressure from combustion will seal it properly in short order once the engine is running.

 

[10K Pete]

What was the blockage!!!???? Gotta know. And yes, use a fine abrasive,
not auto valve compound as it's way too coarse.

What was blocking the intake? Can't leave that issue just hanging!
:shrug:th_wwp

Pete

 

[Brian Rupnow]

Before you tear everything apart, start cutting 1/2 coils at a time off your intake valve spring. If your engine fires at all---if you can get it to run for two minutes even, then the exhaust valve will probably seal itself.

 

[Longboy]

...if you had a few seconds of running, there is no valve leakage unless the adjustment screw has no gap. I use a flat blade needle file across the valve face chucked in the lathe if it looks galled from cutting under a magnifier. Brass valve seats seem to cut smooth every time. Good to hear you got a response from Webster!

 

[simister]

Ok, I will give all your suggestions a try and report back.

Well Pete, you wanted to know what the blockage was. I am embarrassed to say that I forgot to drill the hole through the side of the cylinder to match the valve block inlet. So, as you can see I had no hope of it going. Amazingly, it was still sucking fuel up the fuel line. There was a very tiny gap for the air to seep through. I knew that I had to spot it when the block and cylinder were finished. However, it was a nice surprise to find something obvious.

I am getting close - just a few small fixes to go.

John

 

[10K Pete]

Thanks for the info on the blockage, John. I'd laugh but I ruined a bearing
on a pump once by failing to drill the oil hole thru the new bearing bushing. One of those forehead slapping moments!!

Keep in coming, I'm interested as I have a H&M in the planning stages.

Pete

 

[simister]

Pete, I know the feeling - I felt exactly the same.

John

 

[simister]

Mixed Success today. Very pleased with the results - "She Runs"

I managed to start the engine today and after adjusting the mixture, got it to run for about 5 minutes. Later in the day I ran it again twice, each time for about 5 minutes.

Here is the Problem:

The engine progressivly got harder and harder to start. I realised that I had lost a lot of compression. I pulled the engine down and found there was plenty of compression in the cylinder - Ah! - the problem must be in the valve block as I had previously suspected. I removed the valve block and found that the exhaust valve was leaking again. I pulled it apart and lapped the valve with toothpaste. I then reassembled the valve block and the exhaust valve was still leaking.
The valve seat looks very good, but I am suspect about the valve.

So tomorrow I will make another valve, unless anyone has got a better idea.

Is there any way to test that the valve is sealing in the valve seat without having to reassemble the block each time. This existing valve appeared to be sealing ok until I put it back together.

Anyway, I am still very satisfied that the engine runs.

John

 

[10K Pete]

Do a blow-down test. Put the piston at TDC firing, lock the crank, and
put some air in thru the spark plug hole. I use an adaptor made from an
old spark plug body, gutted, with a male air fitting welded in. Put in 40,
50, 60 pounds and listen at the intake and the exhaust. I use a short length
of tubing like a stethascope and put the far end right into either manifold.
If one of 'em is leaking you'll hear it!!

When you lap a valve, you should see a lapped ring all around the valve
face and all around the seat. If you don't see a complete ring, it's not seated.

Pete

 

[simister]

Thanks Pete,

Yes I have done blow test. I did it a different way, but with the same effect. The exhaust valve is definitely leaking. I need to check if it is the valve guide or the valve that is the problem.

John

 

[simister]

Update:

I have just removed the valve guide from the block. I fitted it in some clear hose (very tight fit). Submerged it under water with the valve inserted into the guide. I then blew as hard as I could through the tube and there were just a few small bubbles.

I really don't think I could improve on this valve seal.

I then had a look around the guide and found carbon buildup under the valve guide and on the inside of the block. I have attached some photos and it looks like the loctite didn't go right around the guide and has left an air gap.

I think this may be the problem.

Any thoughts?

John

 

[Cogsy]

I was going to comment that it's very unusual for a valve to get worse at sealing after the engine begins running on it's own. I think you're probably right about the outside of the guide leaking instead. At least you've heard it run - that should keep you motivated while you fix it.

 

[simister]

It certainly has renewed my motivation now I know it can run.
Just a few fixes to go.

Is there any special Loctite that I should be using on the valve guide?

I have used a permanent high strength thread locker. However, I have some Loctite 609 which is a retaining compound of medium strength.

 

[Cogsy]

I've never built a Webster so I'm not sure what the design of the valve guides is like, but for slip in guides/cages, I use Loctite 635 which is a slip fit Loctite. The various grades of Loctite have differing strengths, but also differing requirements about thickness of the film. It is possible to misuse them by applying one that is designed for use in large gap applications (like threadlockers) in a close fitting application, or vice versa, and you may not get the bond strength you think you should.

 

[Brian Rupnow]

You should lap in two stages--First with 320 grit, then with 600 grit. Toothpaste isn't really good enough for what you are doing.--Voice of experience!!!

 

[Mechanicboy]

It certainly has renewed my motivation now I know it can run.
Just a few fixes to go.

Is there any special Loctite that I should be using on the valve guide?

I have used a permanent high strength thread locker. However, I have some Loctite 609 which is a retaining compound of medium strength.

Use Locktite 638, it is good to fasten the sloppy parts up to 0.25 mm/0.0098 inc clearance and keep temperature up to 180 degree celsius/356 degree Fahrenheit.

I prefer light press fit to mount the bronce sleeve for valve into valve block + locktite on groove in valve block to keep gas tight.

 

[Brian Rupnow]

No Loctite will stand up to the temperature that is seen in an air cooled cylinder head. If you have built the webster to the original design and the valve block is actually situated on the outside of the cylinder, the guides are held in place by a ring around the inside end that keep them from flying out under combustion pressure. However the shoulder above the ring must be a very very good fit into the valve body, and use some loctite too.

 

[Mechanicboy]

You should lap in two stages--First with 320 grit, then with 600 grit. Toothpaste isn't really good enough for what you are doing.--Voice of experience!!!

I used the lapping paste (fine paste) for valve in automotive cars where i am working as car mechanic when i lapped the valves in Webster engine, it can not hurt the valve/seat.

If doubt about the paste is too coarse, you can mix the grinding paste in kerosene to a thinn paste and apply on valve and grind valve in both ways (rotate valve in both ways) until you feel there is not more grinding under work. Then wash the valve/valveblock and examine---> Correct lapped valve ---> Dull ring around valveseats.

Under running-in the engine will improve the valves and last long time.

Tooth paste is not a grinding paste for metal, if case the tooth paste was a gringing paste then your tooth will be grinded away for a long time since when you was a young children.

 

[Mechanicboy]

No Loctite will stand up to the temperature that is seen in an air cooled cylinder head. If you have built the webster to the original design and the valve block is actually situated on the outside of the cylinder, the guides are held in place by a ring around the inside end that keep them from flying out under combustion pressure. However the shoulder above the ring must be a very very good fit into the valve body, and use some loctite too.

Correct, my Webster engine is watercooled..