A Camshaft with Only One Lobe?

[Bruce Wrenn]

In you have ever worked on an engine, you know the camshaft is what controls the valves. One lobe opens and closes the intake, and another the exhaust, with each cylinder having it's own set of two lobes. EXCEPT on a small Honda engines. The camshaft has ONE lobe that controls both intake and exhaust valves, plus cam shaft is made of plastic. Ran into this on a power washer yesterday. Cam lobe was worn, so engine runs terrible. Ordered a new cam (genuine Hond part) off Ebay for less than ten bucks delivered. Installation is super simple. Takes longer to scrape the old RTV sealant off head and valve cover than to remove and replace cam it's self.

[Brian Holcombe]

Bruce, I’m not an expert on two strokes but I believe this is the case because the piston contributes to the ‘timing’ in the sense that it covers the intake and exhaust ports at different positions during the stroke.

[Tom Stenzel]

It's probably a 4 stroke. To shift the opening of the intake and exhaust valves all they would do is make the cam followers not in line, like 90 degrees apart.

A plastic camshaft? That sounds like a weak spot. Bruce, I have two questions: Does the engine require special oil? and do you have any idea how many hours were on the engine?

If it ran daily for 10 years I wouldn't mind it. If it ran a few hours every other year then it sounds like an issue.

-Tom

[Bill Dufour]

AFAIK Rotary engines only have one cam. But they have to have an odd number of cylinders.
Bill D.

[Bruce Wrenn]

It's probably a 4 stroke. To shift the opening of the intake and exhaust valves all they would do is make the cam followers not in line, like 90 degrees apart.

A plastic camshaft? That sounds like a weak spot. Bruce, I have two questions: Does the engine require special oil? and do you have any idea how many hours were on the engine?

If it ran daily for 10 years I wouldn't mind it. If it ran a few hours every other year then it sounds like an issue.

-Tom

Engine is a four stroke, not 2 cycle. This engine is about 15 year old, so premature cam wear isn't a problem. It has a Grimmer type rubber timing belt that is oil wetted. You have to split the crankcase to replace timing belt. To replace cam, you remove valve cover, bring engine to DTC on compression stroke, slide timing belt off cam, then remove pin that cam rides on. Lift cam out and replace with new, adjust valves, and reverse assemble. It takes more time to scrap off old RTV sealant than to do rest of operation. As for plastic cam, B&S has used a plastic gear and lobes on steel shaft cam for years. This is a standard Honda engine, like the ones on the lawn mowers, two of which I have.

[Kev Williams]

Had to look it up, clever way to make a small engine a bit simpler...
1lobe.jpg

[Bruce Wrenn]

Had to look it up, clever way to make a small engine a bit simpler...
1lobe.jpg

Durn Japanese. So simple and it WORKS! Because of the way the crankcase splits, they only have to make one style of cylinder assembly for either vertical, or horizontal shaft engines. The lower half of the crankcase determines which style

[Brian Holcombe]

Awesome! Neat to see such a simple way to do something.

[Bruce Wrenn]

Awesome! Neat to see such a simple way to do something.

Amazing thing is this technology has been around for several years. Must be protected by a patent. By having valves on opposite sides of head, gas flow is much improved. I have two TroyBilt 21" mowers. One has Honda engine, and other has B&S engine. B&S is old style "L" head engine. After cutting grass using either mower, Honda is still almost full, while Briggs uses a quarter tank to cut the same amount of grass.

[ChrisA Edwards]

I can remember reading an article in a motorcycle magazine, almost 40 years ago, where Honda had built an almost total plastic and Nylon engine.

They claimed the plastic didn't need the same amount of lubrication as metal and it was much lighter, something motorcycle manufacturers are always seeking.

Never heard anything more above it.

[Kev Williams]

I can remember reading an article in a motorcycle magazine, almost 40 years ago, where Honda had built an almost total plastic and Nylon engine.

They claimed the plastic didn't need the same amount of lubrication as metal and it was much lighter, something motorcycle manufacturers are always seeking.

Never heard anything more above it.

--Probably because it eventually self-destructed - the- or better I say "a" problem with plastics, is they can become brittle with age, and heat and cold cycling doesn't help. How many of us have had the experience of being stranded, or in my case, had their engine's oiling passages blocked, by the pieces of nylon gears of the engine's camshaft breaking apart, causing the cam to skip time or stop rotating altogether..? And when hard nylon bits find their way past the oil pump screen's failsafe hole, total bearing meltdown can happen within 30 seconds...

Good stuff plastic, when used correctly!

[Dave Cav]

At one high school where I taught the previous shop teacher acquired a pallet load of vertical shaft Honda engines with the split cranksase. Apparently they weren't CARB compliant and Honda sold them for pennies on the dollar (or gave them away) to educational institutions for training. I took one of them apart and found them totally unsuitable for shop class due to the weird design and difficulty in getting them back together correctly. We ended up using Harbor Freight Predator engines for the small engine class; they were much more conventional in design and easy to disassemble and reassemble, and always ran fine if reassembled reasonably well. As far as I know the pallet of Honda engines are still sitting up in the mezzanine above the metal shop.

[Bruce Wrenn]

Installed new cam shaft in power washer yesterday afternoon. Tried it out this morning, and she purrs like a kitten now. Ten bucks well spent!