Tecumseh Hssk50 wont fire

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cfh

Well-Known Member
#1
#1
Have a 1990s tecumseh hssk50. this engine is off a snowblower, and is in very nice condition. the bore is scratch-free, original hone marks still visible. it's a small exhaust valve version. i can not get this engine to fire! here's what i've done/checked...

- pulled the piston, ring gap on top ring down about 1" from top of cylinder is .015". the three rings are properly spaced apart.
- cam/crankshaft alignment gear teeth set correctly
- lapped the valves.
- checked the valve clearance and both at .006"
- no governor, i removed it.
- checked the head for flat surface with blue ink, and it's pretty darn flat.
- new head gasket.
- new spark plug.
- currently bolted to my workbench with no exhaust or intake/carb.

using starting fluid through the spark plug hole, i can't get even so much as a sputter from the engine.
(I'm using a drill to turn the motor, and yes i'm spinning it in the correct direction! ha!)

yes there is spark, and it's robust. but for fun i replaced the flywheel and CDI unit from another engine, no change.
compression is nice too, you can feel it.

now i know this motor ran before, as there was some carbon in the head. not much though, this engine was not run much. the exterior case was pretty clean too. a very lightly used engine. but it sure won't even do as much as a sputter now. even if the compression is low i should get a sputter from the thing...

what am i missing??
thanks!
 
f4radar

f4radar

Well-Known Member
#3
#3
"No carb, no exhaust and starter fluid in plug hole" I've never tried to test a setup like that. Has that worked for you in the past. Maybe try a different plug. I know some of my 20 year old chemicals aren't as potent as they once were. How about a shot of starter fluid in the open intake while your spinning it.
 
C

cfh

Well-Known Member
#4
#4
I always test motors like this with no carb, no exhaust. just put either lacquer thinner or starter fluid in the spark plug hole, screw in the plug and spin the motor. It’s called proof of concept! I always do this on motors just to make sure they’re going to fire. Putting an entire motor all together with exhaust and intake and carb just to see if it fires. And then find out it doesn’t, it’s wasted time and work.

on CDI units there’s no timing to set as far as the electrical. That’s fixed.
 
C

cfh

Well-Known Member
#6
#6
I’ve tried multiple plugs no difference

The compression release is on the cam lobe. It’s not something you can really remove unless you grind the cam.

i’ve had this problem on engines before. Always late model cdi Tecumseh HSSK50 or Lh195 models from the 1990s with small exhaust valve. But usually it’s because the engines are hammered. This engine is nearly new condition.
 
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C

cfh

Well-Known Member
#8
#8
in the past it's been with motors that are pretty spent. so i tend to just part them out.
this is the first time it's happened on a motor that had a perfect bore and no apparent wear
 
ole4

ole4

#13
#13
So assuming you have fuel, adequate spark at the right time, and compression, my guess is too lean a mixture as with no carb and an open inlet port it’s getting as much air into the cylinder as possible.
 
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cfh

Well-Known Member
#14
#14
Ole4 but i always fire my tecumseh hs50 engines "bare" like this on the bench. and they always generally work. and if they don't, after putting them all together with intake/carb/exhaust, they don't fire all assembled either... that's why i do it this way, to get the kinks ironed out. i can even *hear* problems on a simple 2 second starting fluid run on the bench (like low compression.) but this one i can't get to even sneeze. it's so weird, i can't figure it out...
 
sparkwizard

sparkwizard

#15
#15
Just guessing, but maybe the small valve version moves air with enough velocity to lean out the mixture so no fire?
You did say you've had this problem with other small valve engines.
 
C

cfh

Well-Known Member
#16
#16
now that you mention it, not sure i've ever fired a small valve HS motor this way on the bench. (i try and stay with large exhaust valve motors, but the late model HS motors are abundant.) I have other engines laying about, let me try another small valve HS as a comparison, and i'll report back, hopefully later today...
 
sparkwizard

sparkwizard

#17
#17
I thought the small valves were supposed to induce some kind of swirl in the chamber to decrease fuel demand.
I remember Ford and their HSC (high swirl combustion) and Honda with their CVCC (controlled vortex combustion chamber) in the eighties and nineties. I think small valves and tiny intake runners were an attempt to reduce emissions.
 
C

cfh

Well-Known Member
#19
#19
grabbed another motor from the stack. a late 1990s Hssk50 off a snowblower, with small exhaust valve. now i did nothing to this motor as of yet. just took out the spark plug and dumped some lacquer thinner into the spark plug hole. replaced the plug and turned the motor with the drill. It sneezed, unlike the other (black) motor. also the compression on this naked motor feels about half of the black motor. so what the heck is going on here??? there's gas... there's compression... there's spark... what the hell??

m.jpg
 
M

mchadsey1

Member
#20
#20
cfh said:
grabbed another motor from the stack. a late 1990s Hssk50 off a snowblower, with small exhaust valve. now i did nothing to this motor as of yet. just took out the spark plug and dumped some lacquer thinner into the spark plug hole. replaced the plug and turned the motor with the drill. It sneezed, unlike the other (black) motor. also the compression on this naked motor feels about half of the black motor. so what the heck is going on here??? there's gas... there's compression... there's spark... what the hell??

View attachment 313070
Click to expand...
Start swapping parts and tell is what you find. If you have air fuel and spark somthings not in sequence . Id remove the flywheel first and look to see if the flywheel key is sheared.
 
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