Webster Build

[Brian Rupnow]

Can anyone give me some ideas where to start looking for the spring steel for the rocker arm?

The rewind spring from a chainsaw, lawnmower or weed-eater all are close to the right size and work very well.---Brian

 

[Blogwitch]

Get hold of a piece of the metal banding that is used to fix things to pallets etc.

John

 

[simister]

Thanks Guys, That should be easy enough to get hold of.

 

[simister]

I have finished the connecting rod. This was a challenge for me to do. I made a rough cut first and finished the ends with a rotary table.

 

[simister]

I am about to start the exhaust cam. I am having some difficulty getting my head around doing this part. Any advice on doing this would be a appreciated. I do have a rotary table. I have machined the diameter to .712 and reamed the centre hole.

John

 

[gus]

Hi John,
The Con Rod very well done and profiled. I did a lousy job with mine and had to file and manual finished to remove flaws. The DIY RT was not well made and did chattered. However a new RT was made and no more chatter with subsequent con-rods.

 

[Brian Rupnow]

see post #139 here.--Brian
http://www.homemodelenginemachinist.com/showthread.php?t=7687&page=14

 

[simister]

Thanks Brian, Looks fairly straight forward. The finished result of the exhaust cam looks very good.
I will post my attempt when finished.

Gus, I also had to do some filing to clean up some machining marks on the con rod.

 

[simister]

Well, I finished the exhaust cam today. I followed Brian's post in the procedure. I scribed the required diameters and tangent lines on the cam. I machined some mild steel with a spigot to take the cam, I then tapped a thread to take a cap screw to hold the cam in place. I was now able to hold the cam and have some sanding guide lines. I then used the belt sander to follow the shape. It is not perfect but the dimensions are as required, so, I am hoping it will work ok.

I also machined the cam gear to take the cam.

 

[simister]

I have finally finished the cylinder. I have honed the cylinder with a brake hone and it looks fairly good. However, I have been reading some other posts since I honed and I am now not sure if I should of lapped it with a lapping tool. I am going to use the Viton o-rings on the piston. I am quite pleased with the way it turned out. I notice on the plans that is says not to polish the bore as the fine grooves help to hold the oil.

 

[werowance]

it is my understanding that honing is done for engines with rings in order to do 2 things, 1 is oil control and the other is to make the ring rotate or spin.
the scratches help hold oil on the walls of the cylinder and the cross hatch pattern I have been told (others more learned than I should correct me here) will cause the ring to spin on the piston as well.

lapping is for example a 2 stroke engine that has no rings. like the rc aircraft engine I am working on so the cylinder is slick and smooth because there is no ring and the piston must fit almost perfect to the cylinder.


edit - I know the Webster plans call for rings so I would say you should hone it. if you are subbing an oring for rings then I would not do a course hone job because it might wear out the rubber ring quicker.

 

[simister]

it is my understanding that honing is done for engines with rings in order to do 2 things, 1 is oil control and the other is to make the ring rotate or spin.
the scratches help hold oil on the walls of the cylinder and the cross hatch pattern I have been told (others more learned than I should correct me here) will cause the ring to spin on the piston as well.

lapping is for example a 2 stroke engine that has no rings. like the rc aircraft engine I am working on so the cylinder is slick and smooth because there is no ring and the piston must fit almost perfect to the cylinder.


edit - I know the Webster plans call for rings so I would say you should hone it. if you are subbing an oring for rings then I would not do a course hone job because it might wear out the rubber ring quicker.

Ok, that all makes good sense. The bore looks to be smooth, maybe, slightly scratched but extremely minor.

Thanks for your advice.

John

 

[Cogsy]

I've only ever used cast iron rings and always go for the honed finish. However, Brian Rupnow uses viton orings and he always laps the bore to a very fine finish or the orings wear very fast. If you search for one of his builds (like the rupnow hit and miss engine) there should be some nice pics of the finish on his bores.

 

[Blogwitch]

Sim,
You have done the right thing with the bore, honing puts the fine scratches on the cylinder walls, allowing the metal rings to bed in nicely with the bore, but I don't know how well the viton ring will stand up to rubbing against the roughish surface left by the hone.
Maybe you should have lapped it after all, as that should give a highly polished bore, usually associated with steam or air driven engines that don't usually have a running in period.

John

 

[crankshafter]

John.
I have Vitonrings on my Webster and on my Hoglet. I have lapped cyl.on both. They'r runnig great, and have no lack of compression after many houers.
Btw. I just come in from my shop after running them. Usualy start's on first flick;D

Best reg
CS

 

[simister]

Ok, it looks like I need to get the bore smoother if I am going to use Viton O-rings. I have a brake honing tool which has fine grinding pads on each leg. What is the best way to lap the bore? Can I make a lapping tool to do this job?

 

[gus]

John.
I have Vitonrings on my Webster and on my Hoglet. I have lapped cyl.on both. They'r runnig great, and have no lack of compression after many houers.
Btw. I just come in from my shop after running them. Usualy start's on first flick;D

Best reg
CS

Hi Crankshafter,

Long time no see your posts. Now in the midst building the Howell V-2 which will require 16 spur gears for timing and oil pump. 16 spur gears to cut tooth by tooth will take some time.

Trust all is well at home.

 

[Brian Rupnow]

Simister--Just go ahead and use a viton ring with the bore the way it is now. After half an hour the o-ring will be worn out, but the bore will be polished smooth. Then pull the piston and change the o-ring for a new one.---Brian

 

[simister]

Simister--Just go ahead and use a viton ring with the bore the way it is now. After half an hour the o-ring will be worn out, but the bore will be polished smooth. Then pull the piston and change the o-ring for a new one.---Brian

Thanks Brian, I have already purchased extra O-rings as spares.

 

[simister]

I have now machined the groove for the viton o-ring. I was concerned about going to deep with the groove and having to make a new piston. So I crept up on the depth and kept trying the o-ring. Like Brian, the width is a fraction wider than I would of liked but I think it will still be OK. It is very tight to move in and out. I am expecting it to loosen up with some wear.

Brian, I read in your post that you also experienced the same tightness. Did you find that it loosened up much with some running in? I am in the dark how tight this piston should be. If I machine it so it moves freely, I may find that it is too loose after running in and have no compression.

John