Adjusting my valves?

[pequeajim]

I was cutting grass and all the sudden my 425 was running like it had bad gas in it. I knew the gas was fresh, so I looked elsewhere. When I tried to restart the engine, I could hear a popping sound almost like it was backfiring in the carb. I took the filter off and looked at the carb, and there was a lot of oil in the pan. I cranked the engine and could see a discharge out the carb.

I pulled the left plug and it went away. This made me suspect maybe a stuck valve. I pulled the valve cover and low and behold, the exhaust side push rod could be moed around by hand and the rocker arm was so loose it could be rotated off the rod. I'm not sure how long it has been like that.

I tightened things up just enough to get the 425 back to my barn, but want to look at and adjust both sides. I looked on the Robin site for information on how to do this but could not find anything in the service manual.

Any ideas? Isn't there supposed to be a measurable gap, and how do I set it?

 

[pequeajim]

oops!

I looked in a different spot on the site and found the reference to fixing my problem.

Thanks Robin for putting the information up on the site in such an easy spot that I missed it!

I've got to change those glasses..!

 

[Marks481]

Hey, maybe this is the same problem that Central_PA_Chris is having... he said that his air intake filter had gotten soaked by oil.

Thanks for the post; sounds like maybe some preventative maintenance might be a good idea for those of us with Robin engines. 10 minutes now might save some grief later. Did you have to replace the valve cover gaskets when you adjusted your valves?

In my youth I had a old ugly green Porsche 914 (actually more like the anti-Porsche)... with the VW flat 4 engine, I generally did valve adjustments every time I changed the oil. I bet the PT will be alot easier (not having to crawl under a car and work over the engine, which was crammed in a little compartment in the middle of the car).

 

[SnowRidge]

Do the Robbins have regular adjustable valves? The Kohler 25s have hydraulic lifters, which sounds good, but they have had a lot of trouble with them. I think I would prefer adjustable valves with solid lifters.

 

[pequeajim]

I would think that it might be a good idea to check the valves every 150-200 hours. The problem with mine is that the rod came loose. I'm very lucky that it did not do any damage!

I will be checking them after 50 hours, and then every 150 hours.

I ordered a few sets of valve cover gaskets too, just in case.

(must be something about us central PA guys...)

Hey, maybe this is the same problem that Central_PA_Chris is having... he said that his air intake filter had gotten soaked by oil.

Thanks for the post; sounds like maybe some preventative maintenance might be a good idea for those of us with Robin engines. 10 minutes now might save some grief later. Did you have to replace the valve cover gaskets when you adjusted your valves?

In my youth I had a old ugly green Porsche 914 (actually more like the anti-Porsche)... with the VW flat 4 engine, I generally did valve adjustments every time I changed the oil. I bet the PT will be alot easier (not having to crawl under a car and work over the engine, which was crammed in a little compartment in the middle of the car).

 

[Marks481]

Service manual calls to check valve clearances every 500 hours. Probably would have been prudent to have done that after the initial 20 hours break-in period instead of waiting so long. Guess I better get busy.

 

[Central_PA_Chris]

Hey, maybe this is the same problem that Central_PA_Chris is having... he said that his air intake filter had gotten soaked by oil.

Interestingly enough that's the solution Robins came up with too, they also said if the valves where malfunctioning while hot, this could cause yet more heating, basically a positive feedback loop causing the heating and boiling gas I get on relatively cool days after relatively low periods of run time. I'll still move the gas line/replace it with real gas line, but this gives me some hope that a bunch of my issues will be nailed with this latest round of under warranty shop work. Then just gotta nail down the wheel circuit hydraulic issue and maybe, just maybe, I'll have a fully functional 425.

 

[ponytug]

This sounds great! It smells like a solution. One thing that has always bothered me about the issue of the PT 425s vapor locking is the variability. Some people have it, some don't, some solutions work for some, and not others. If the PT design runs warm, then a variance in the valves might account for the individual differences.

Regardless, I hope it works!

All the best,

Peter

Interestingly enough that's the solution Robins came up with too, they also said if the valves where malfunctioning while hot, this could cause yet more heating, basically a positive feedback loop causing the heating and boiling gas I get on relatively cool days after relatively low periods of run time. I'll still move the gas line/replace it with real gas line, but this gives me some hope that a bunch of my issues will be nailed with this latest round of under warranty shop work. Then just gotta nail down the wheel circuit hydraulic issue and maybe, just maybe, I'll have a fully functional 425.

 

[SnowRidge]

This sounds great! It smells like a solution. One thing that has always bothered me about the issue of the PT 425s vapor locking is the variability. Some people have it, some don't, some solutions work for some, and not others. If the PT design runs warm, then a variance in the valves might account for the individual differences.

All kind of factors can come into play. The 10% alcohol fuel seems to be worse than straight gasoline, or a mix with less than 10% alcohol. Fuel line length can be an issue, too. My machine came with an extremely short fuel line. It was just long enough to reach, which made it not long enough if I had to drain the tank into a container.

I replaced all the fuel line recently. I put the the new line in with a moderate loop down into the bowels of the machine so that it would be long enough if I needed to drain the tank. All of a sudden, I was having vapor lock issues, especially as the tank level got lower (lesser head pressure). Shortening the line up to its original configuration took care of the problem.

 

[ponytug]

Snowridge:

This is exactly my point. While it is true that there is a flow resistance moving a fluid down a pipe, gasoline isn't very viscous, the PT fuel line is reasonably short and a little extra loop shouldn't have added that much more resistance to flow. If adding another 18" of fuel line triggers vapor lock, the basic setup has to be routinely close to vapor lock, so any one of some number of issues could push it over the edge.

The 10% ethanol problem makes complete sense, as that mixture has a lower vapor pressure, and would therefore be more prone to vapor locking.

All the best,

Peter

All kind of factors can come into play. The 10% alcohol fuel seems to be worse than straight gasoline, or a mix with less than 10% alcohol. Fuel line length can be an issue, too. My machine came with an extremely short fuel line. It was just long enough to reach, which made it not long enough if I had to drain the tank into a container.

I replaced all the fuel line recently. I put the the new line in with a moderate loop down into the bowels of the machine so that it would be long enough if I needed to drain the tank. All of a sudden, I was having vapor lock issues, especially as the tank level got lower (lesser head pressure). Shortening the line up to its original configuration took care of the problem.