HS50 has no power under load.

[Rapidrob]

I had posted that my HS50 with very low hours on it has low compression ( 55 PSI). One of the new carbs came in and I got the engine to run well even at a slow idle now. After letting engine warm up for a few minutes, I took my bike ( Hilltopper) for a ride.
All things mechanical freely turn ( it does have a V-Belt TAV ) but the bike has no power. Any slight hill starts to bog the engine down.
And yet, if the bike is on a stand, the engine speeds up happily.
There is a slight puff of white smoke at a re-start, it does not smell like oil.
When I was doing compression test I noted that after I had pulled the engine rope starter several times and pulled the head off, there was a layer of oil on top of the piston and the valves. I don't know if this is normal or not?
When the engine is running there is a mechanical knock I can hear, It is not a gasoline ping. Since I'm not familiar with this engine like you guys are, I don't know if that is normal or not?
Do I have bad valves? a bent rod?, there are no scores in the cylinder what so ever as the engine, as I'm told , only has two to three running hours on it. And it looks it.
What say you?

 

[superflea]

I'm a dummy but it sounds like bad rings and possibly rod bearings (knock) I had a 200hp Evinrude that drove me nuts. The compression tested good and it idled and revved fine until I put it on the water, then no top end and really sluggish. It was the leak down compression that was the prob. That's the ability for the engine to MAINTAIN the compression before ignition. Compression tests are usually looking at peak compression. Either way with the knock you are looking at a teardown.

 

[superflea]

BTW oil in the combustion chamber could be valve journals but with your symptoms it sounds more like blow by around the rings.

 

[pomfish]

Sounds like a couple things at once...Maybe.
The knock you hear "may be" the piston going onto hydraulic condition, in other words the oil is compressing on top of the piston but it cannot compress like gas vapors so it pushes back. Or your plug is too long and hitting piston but that would be real loud.
The white puff is most likely due to sticky valve and or weak valve spring.

I have a 12HP Kohler on the Cub Cadet that has sticky valve, will do the white thing, load up, no power, but if I let it warm up ever so slow and increase speed eventually she will break free and run good.
Marvel Mystery oil has got her to where she rarely throws a fit unless it has sat a couple months.
Slam the Marvel in the engine oil and in the gas. Great stuff.

You could always pull the side case undo rod cap and release the piston and make sure the rings gaps aren't lined up too close to each other as well.
Losing compression somehow.
Let us know hat gives.

HTH
Keith

 

[Rapidrob]

I may have to pull the engine apart to see what is going on. It does have the decompression cam lobe, but the engine should still produce much more power than it is. Really good throttle response, just no power as it should have.
I'm going to change the air filter type and double check the throttle linkage. I'll throw in a new spark plug as well.

 

[Rapidrob]

I took the new carb apart and cleaned it. I put on a low restrictive air cleaner and re-designed the throttle linkage The engine runs a lot better now but still lacks some power for what a 5 HP engine should do.
I wonder id that stupid decompression lobe is the problem?
I'm trying to record the knocking sound.

 

[Rapidrob]

Here is a 20 second video of the engine at a slightly fast idle. Turn your sound up and you can hear the knock.
Is this normal for this engine?
It does have the cut off PTO shaft.
The knocking sound is on the left side of the engine ( camera side)

 

[old shed finds]

On my phone it sounds like too much valve lash.. Ticking..
But it is true that the oil control ring is shot...or sucking oil through the valve guides.

 

[Phil1958]

air leak......

 

[Rapidrob]

The air intake and new carb all have new gaskets.
Are the vales adjustable in this engine?
There is no white smoke under load or at idle, just at start up. and it is just a wisp of smoke, not a cloud.
I drove the bike for five miles. Max speed is supposed to be 20 MPH, it may be in the teens but not 20 for sure. My app for speed keeps losing the GPS lock on so I just guessing at speed. This bike is really geared LOW. The main driven ( on rear wheel) sprocket is huge, perhaps 60 tooth and the drive chain sprocket is 15 tooth. No idea about the TAV.
This bike has a strange TAV,unlike any I have seen before. Very skinny drive V-Belt. It could be slipping but it does not feel like it is. At idle it grabs a little, doesn't slow the engine down at all.
I kept playing with the carb ( CHI-COM long lever choke) and I can see why folks don't like this carb. It does not seem to breath well under open throttle.
I am at 7,000' ASL it could be a jet problem?
The more I run the engine under load the more it seems to be getting a little better. With the engine only having 2-3 hours on it before I got it and it sat for 10 years, the valves maybe needed to reseat themselves.

 

[Havasu Dave]

I couldn't hear any knocking, but this is a bad way for anyone to determine anything. If there is knocking on the PTO side, it is either your clutch on and off the engagement, and/or too much end play on your crankshaft. The latter wont really affect your performance under load, but you've already said the clutch is grabbing a little, so that may very well be the source of that sound. That clutch may also be affecting the performance.

A lot of advice on this forum comes from OHV or automotive experience, which is fine, but the valves and rings for the most part, even on low hour engines are looser than even the specs call out in the service manual. No, the valves are not adjustable. It is normal to see a bit of oil on top of the piston if a cold engine was shut down. But if oil flow through the rings or valves were causing poor performance, you would see that blue oil all the time.

The carburetors on these engines are designed to run at a fairly constant speed as dictated by load via a governor. They were not intended for acceleration and deceleration like on mini bikes. I think we sometimes lose sight of that. I am sure you know that no speed records are ever made at Denver's Mile-High drag racing track. 7000 feet? That's a lot of load for a 5HP flat head. Not too much load, but a lot of load. There are no changeable jets in your carburetor, but the altitude means less fuel for you, not more, and any pressure density issues are adjusted by shutting the main jet down a bit. You are starving for air, so you need less fuel.

Now that I've run my lips far too long, I'll go back to the original thought I had, and that is to get a replacement torque converter and try again, and I bet most of what you describe goes away. But it will still perform like 100 years of flat head design unhampered by technology does.

 

[Rapidrob]

I do need to replace the whole TAV as the original is only using a 3/4" wide V-belt and the clutch is either fully open or closed,there is no progression at all.
Thank you for the info. I do have just a Comet clutch side to give it a try for the noise.

 

[Mariah]

Well … I'll be a monkeys aunt if that's not too much valve clearance or a sticking valve!

 

[pomfish]

Or weak/broken valve spring.
Need to pull that side case.

 

[minibikin']

Wouldn't the easiest way to trace the noise be removing the clutch/tav and running the engine? There's some good info here, but I wouldn't pull anything until I was pretty certain what was causing it. It's super difficult to diagnose anything through a phone video and I really don't hear too much out of the ordinary...

 

[Mariah]

If the TAV grabs, slow the idle down a little and rub foot powder or talc powder on the sides of the belt. The powder lets the belt hook up smooth and move across the sheaves freely!

 

[Rapidrob]

The noise is there with nothing connected to the engine.
I will need to pull it off of the bike and check out the valve springs. They were good before I mounted the engine and started it up.

 

[Mariah]

While you have the breather cover off soak the valve stem guides with spray gumout, if there is varnish from stale gas interfering with valve movement that will loosen them up.

 

[Rapidrob]

Here is the TAV that came with the bike.

I removed the engine from the bike and put it on a stand I made.
I double checked the valves and springs,both are like new.

Running the engine the noise was coming from the center of the engine.
I pulled the engine apart to see if there was any parts broken. There were none. I did notice the connecting rod had a very slight play in the end cap
as the piston went from fully down,to starting the upward swing. This I guess is normal?

I took the engine completely apart looking for any problems. I only found two.
One-The oil was really dirty and dark gray,not black. Since there is no water in this engine it had to be blow-by gasses were contaminating the oil.

I removed the piston and "superflea" was right on the money. Both top piston rings were in perfect alignment at the ring gap!
Oil ring is OK.
This engine really does only have a couple hours on it. There was very little wear any place I looked.



The 2ND thing I noticed was a very slight scratch on the connecting rod journal and the bottom of the rod.

I never knew there were no replaceable bearings in these engines.
I looked at the cam and sure enough there was that darned decompression "bump'.

I took it to my Dremel belt sander and very carefully removed it and contoured the face of the cam to match the "closed" area.



Now I need to think about replacing the connecting rod,or just make a positive stop for the throttle as I removed the plastic governor assembly.
I don't plan on ever running the engine at really high speeds.
I don't not have a valve spring compression tool for these little engines.
Tearing an engine apart,it just is not worth the money they ask for a "real" compressing tool.
I took a length of 1/4" x1 1/4" flat stock and ground an end to a bevel. I then notched the tip to just slide past the valve stem.



I then use a 1/2" Allen wrench as a steady rest . I poke the tool one coil above the retaining ring and push down on the tool compressing the spring.

The spring is compressed with little effort and the retaining cup fell right off. Both valves were out of the head in less than a minute.
The valves and their seats look new.
The case half's had never been separated since assembled. I have to get a new gasket and some Gray RTV.
PTO was cut off flush with the side of the case. I may do the "Freeze-plug" trick after shorting the shaft.
I got to get my ducks - in-a-row now and decide on the next steps to take.

 

[Rapidrob]

I'm keeping the original connecting rod,I really don't plan on doing any high RPM runs. The engine is 2 HP too low already for this bike.
I aligned the rings on the piston as shown in the service manual and reinstalled the cam and valves.
I ordered the gasket kit as the engine block gasket tore in several places.
Now hurry up and wait for the parts.