HS40 exhaust valve wobble?

[keaton85]

Figured you guys are the best to ask about HS40 motors so here it is...

Picked up a old HS40 that looked to be rebuilt by the massive patch of JB weld right under the fuel tank on the block! Anyway, I rebuilt the carb, new fuel lines, filter and so forth. Ran great!!!! But then it wouldn't....

Long story short, I pulled the head and found that when on the compression stroke the exhaust valve lifts ever so slightly off the seat wobbles a touch then reseats back about half an inch before the piston hits TDC. strange right?

So what can cause the exhaust cam to lift off the seat during the compression stroke? it seats fine when the piston is at BDC but right in the middle of TDC and BDC it lifts off the seat by a 1/16th or so!

Retarded issue as compression reads 95-100PSI but takes a few revolutions to get there. Looking like good compression but it's not due to the exhaust valve lifting off the seat.

 

[kzhorse]

Sounds like a compresion release to help make it easier to start,Should be normal.

And welcome to OBM.


Scott

 

[roccosbike]

He he, that is the compression release ground into the cam.What you want to check is your valve lash.I bet that is whats wrong.

 

[keaton85]

sounds good but what I don't get is that I can not get this motor to run anymore.

Good compression
New plug
rebuilt carb
cleaned twice (once to get it running great, then second when it stopped running correctly)
New tygon fuel lines
Fuel filter
New fuel
great blue spark

But it will not stay running! sat for ONE night after running flawlessly.

How would valve lash effect this if I'm getting good compression? seams like I would get poor compression if valve lash was out? also would that happen overnight?

 

[roccosbike]

Check the magnets inside the flywheel. I guess it will be a process of elimination.Its hard to diagnose something without putting your hands on it

 

[ATKRIDER]

Compression release on a HS40 cam is on the intake side-I only have seen them on the Rupp spec engines. Right after compression when rotated by hand YES the exhaust valve will JUST lift off the seat and than close. Don't ask me I didn't design it, I just build them after the fact. The wobble is probably just above average guide/stem wear OR someone ground the end of the valve stem at an angle.

Anyway-my thought for the day. It partially sheared the flywheel key when it shut off.:drinkup:

 

[ATKRIDER]

OR-It's just out of gas. :doah:

 

[oldfatguy]

check your fuel flow, there might be something clogged in the tank or carb fuel inlet. also check your flywheel key. Did you clean the two holes in the main jet ? I had all kinds of problems with one of my tecumsehs because it sat so long that the gas in the tank turned to varnish. The problem was no matter how much I cleaned the tank the stuff would melt a little at a time and clog up the carb. Even a fuel filter didn't help.

 

[george3]

I use a clean spray bottle with a bit of gas in it spray a small amount at a time in carb. get it running and keep spraying a bit at a time, it will stay running if it has a carb, issue. If it dont run its not a carb. issue. Couldnt hurt to check the throttle plate to see if there is a issue first. Avoid spraying the muffler, :laugh::laugh::laugh:

 

[keaton85]

- Fuel tank is 100% clean with a full tank
- Tygon fuel line with a visu-filter (large stone filter)
- full bowl of fuel with no issue in flow
- carb clean (idle jet ball rattles, all ports cleaned, welch plugs removed and cleaned)
- new intake gaskets

The ignition is a megneto flywheel system, how would the magenets effect this as it's not points or CDI?

Possible issues:
- When I removed the brass insert that runs from the main jet to the venturi (can't remember it's name) I had to screw into the end of it to pull it out. then when I reinserted the brass rod I used the main jet to screw in a press the rod in. Does the rod have to sit a little off the pain jet bolt? or can it be mated together? idono how to explain that!
- The crank has side to side play of about 1/16-1/8th

What happens when I try to get it going:
- throttle set at half
- chock one click from full chock
- engine starts, runs for about 3-4 seconds then dies (no throttle input will help)
- sometimes once it does a puff of white smoke comes out of the carb
- fuel will spit out of the carb if I keep going like this with the chock on
- No amount of idle or main jet adjustments help
- will not even fire without the chock even when there is fuel in the venturi

I feel like a retard here, I have done this a zillion times. This motor ran perfect, sat one night and now it's got nothing. I set the carb up correctly with float level, genuine rebuild, perfectly clean...

The key for the flywheel is the only thing that sounds like a suspect in this frustration.

Thanks for your help guys!!

 

[keaton85]

Compression release on a HS40 cam is on the intake side-I only have seen them on the Rupp spec engines. Right after compression when rotated by hand YES the exhaust valve will JUST lift off the seat and than close. Don't ask me I didn't design it, I just build them after the fact. The wobble is probably just above average guide/stem wear OR someone ground the end of the valve stem at an angle.

Anyway-my thought for the day. It partially sheared the flywheel key when it shut off.:drinkup:

are you saying that the intake should have the release?

I'm getting the exhaust valve open on the upward swing on the compression stroke right in the middle of the stroke. is that not normal?

 

[keaton85]

Update: Yup, sheared the key right off! The flywheel bolt was almost finger tight and I just tapped the flywheel off without issue. Is there a better key that I could use?

Also, I have a good amount of in and out crankshaft play. Is there any way to fix the play or just run it?

Thanks guys!!!!

 

[ATKRIDER]

Actually the crank end play on these almost always seems excessive. You could check it with the engine together with a dial indicator but unless someone has been in there not sure what the point would be-that's probably not what caused the sheared key, the loose nut was or just age and use. A "better" key isn't going to do anything except assuming you mean harder key will just f-up the flywheel OR crank if it does it again. My deal is to use a drop or 2 of like red loctite on the crank taper, install the key/flywheel and torque to specs-like 30 ft. lbs. DON'T use an impact to tighten the nut. I have seen the steel flywheel hub insert split from doing so. IF you use the loctite just make sure and let it sit overnite before firing it up so the stuff gets a chance to set up. Works everytime for me-

 

[The Restore Kid]

WOW you pulled that emulation tube out? :doah: That is a MAJOR rebuild.. :laugh:

If you are looking through the throt of the carb, there should be somewhere in the neighborhood of 1/8 inch of that brass tube exposed in the bore of the carb..

 

[keaton85]

Used a B&S key and blue lock. I don't have a torque wrench on me but I got it tight enough that it should be around 30-40 ft. lb. Thanks for letting me know about the impact! as I would have zapped it....

The in and out shaft play it .032 inch. and the motor has been apart from what I can tell as the case has a MASSIVE JB weld job under the fuel tank. Also the piston looks brand new and I get 100PSI which is pretty good correct?

Anyway, I'm going to finish it up tonight and see how it runs.

 

[keaton85]

Update: Runs great, just needs a little tuning and it will be good to go. Just need to find a PDF for torque specs and so forth to double check a few items.

Thanks again everyone!! almost ended up with a Honda clone just because of a stupid $2 dollar part....

 

[Dave Moore]

Came across this post while searching for exhaust pipes for my H40....

I know this thread is old, but I just want to say that I too have seen my exhaust valve lift slightly just before tdc on compression stroke. I opened the crankcase and removed the camshaft, there's a pin next to the exhaust lobe that is attached to a centrifugal weight beside the cam gear(H40). Clearly its only used to start the engine by eliminating some of the compression but when it's running, the centrifugal weight is tossed outward and the pin retracts away from the lifter.

A decompression pin on the intake valve is totally asinine as you are trying to pull air into the cylinder and having compression go back out through the intake while cranking just doest make any sense to me.... Not trying to come across as a wise guy.....

 

[ole4]

There are two types of compression release on the hs series one like yours with the weight and the other is a bump on the intake base circle. IMHO the weight type is better as the bump still bleeds off compression a bit while it is running.

 

[MB165]

" -chock one click from full chock"

use full choke for a cold engine.....always, half choke and your gonna pull your arm off with no results

check for slop in the throttle shaft too where it enters the carb, if its loose, thats a vacuum leak, it usually will affect idle

 

[JohnnyTillotson]

sounds good but what I don't get is that I can not get this motor to run anymore.

Good compression
New plug
rebuilt carb
cleaned twice (once to get it running great, then second when it stopped running correctly)
New tygon fuel lines
Fuel filter
New fuel
great blue spark

But it will not stay running! sat for ONE night after running flawlessly.

How would valve lash effect this if I'm getting good compression? seams like I would get poor compression if valve lash was out? also would that happen overnight?

You didn't see something fly out of the breather and/or intake manifold did you???