HS50 shearing key

copyman

copyman

Well-Known Member
#1
#1
Rebuilt this HS50 and it starts & runs good for around 5 minutes then shuts off while adjusting carb. When I try to restart it won't start after many pulls, check for spark, no spark. Take flywheel off and key is sheared in half. This has happened 3 times now with new genuine TEC keys. Not sure if shuts off because I'm trying to adj carb or the key shears while running? Also not sure if shearing of key is from many pulls trying to start after it shuts off.

Any ideas what it could be?

Thanks for the help.
 
Skipp

Skipp

#2
#2
If you’re having many pulls after shut of its because the key is sheared, because, in my opinion, it is not in correct time….It was brought to my attention, “is the key shearing because Its back fire from carb adjustments or is it from being out of time from the start”….there is your conundrum….do you time your motors with a dial indicator? Do you time it btdc? Sounds like you should leave carb alone for now and focus your attention to the timing? Also maybe check to see if you have any valve lash? It requires some…
 
Last edited:
copyman

copyman

Well-Known Member
#3
#3
Skipp said:
If you’re having many pulls after shut of its because the key is sheared, because, in my opinion, it is not in correct time….It was brought to my attention, “is the key shearing because Its back fire from carb adjustments or is it from being out of time from the start”….there is your conundrum….do you time your motors with a dial indicator? Do you time it btdc? Sounds like you should leave carb alone for now and focus your attention to the timing? Also maybe check to see if you have any valve lash? It requires some…
Click to expand...
Thanks for your reply. I will check timing with dial indicator. I didn't time engine with this "semi" rebuild because engine looked to be clean & hardly used so I didn't remove stater and could see it was never moved from factory setting. When it started right up and ran really good I figured timing was ok.

So just to be clear an engine can shear the key while running? I didn't hear engine back fire etc. It seemed like it was running smooth except rough idling and why I was trying to adjust carb.

Thanks again
 
copyman

copyman

Well-Known Member
#5
#5
creia said:
Did you properly torque the flywheel/crankshaft nut while tightening it with an actual torque wrench to specs for your engine?
Michael
Click to expand...
Is this that critical? Out of all the engines I've done I hand tighten the flywheel nut without torque wrench and never had an issue with keys breaking. The HS50 torque spec is 450 in. lbs. but my torque wrench only goes to 250. I'm able to torque all the other bolts except the flywheel nut with wrench I have.
 
creia

creia

#6
#6
Yes, it is "that critical". Get yourself the proper tool for the job. You can get a 3/8" drive basic torque wrench at Harbor Freight for about $ 20.00. I have been using mine for dozens of engine rebuilds over the last 15 years.
Michael
 
copyman

copyman

Well-Known Member
#8
#8
After rebuilding 20+ engines I must be really lucky to never have a key shear. I do everything by the book except the flywheel nut which I've always tightened by hand.
Just so this makes sense to me, if not torqued to spec what would cause the key to shear, being to loose? Each time I had to pull flywheel to replace the broken key had to use the flywheel tool because FW was on tight? I remove nut with impact wrench but always tighten by hand.

Thanks again for the help
 
P

panchothedog

Well-Known Member
#9
#9
If the flywheel is torqued properly it doesn't even need a key. The key is to help you get the flywheel in the proper timed position, not to hold it there.
Watch the video by JODY at ARC racing on installing a flywheel with a degree wheel. By the way, if you've built 20+ engines and have never used a torque wrench on the flywheel you have been MORE than lucky. Do like
creia says, go to H F and spend spend $ 20 and get the tool to do the job.
 
copyman

copyman

Well-Known Member
#10
#10
panchothedog said:
If the flywheel is torqued properly it doesn't even need a key. The key is to help you get the flywheel in the proper timed position, not to hold it there.
Watch the video by JODY at ARC racing on installing a flywheel with a degree wheel. By the way, if you've built 20+ engines and have never used a torque wrench on the flywheel you have been MORE than lucky. Do like
creia says, go to H F and spend spend $ 20 and get the tool to do the job.
Click to expand...
Good to know. Thanks for info. Will get the proper torque wrench.
 
E

EricD..

Member
#11
#11
Same thing happened to me. Always just tightened by hand. I used a torque wrench on my HS50 and was surprised how much farther it went before the wrench clicked. Have not sheared a key on it since
 
C

cfh

Well-Known Member
#12
#12
Key sheer can happen for other reasons not mentioned above. For example if the flywheel nut got "loose", and the motor ran a while like that, the keyway can widen on the crankshaft. it does not take much for this to happen. and then even with a properly torque flywheel, the wheel can shift and cut the key in half. short of a new crank, it's a hard thing to fix. this can happen more so with a heavier cast iron flywheel than say an alloy aluminum flywheel.
 
Skipp

Skipp

#14
#14
They use those, well something like those at work…they swear by them….they have a tool allowance too….trying to get my maintenance buddy to “loose” his….he’s a tight bastard….
 
M

Mark Brooks

#15
#15
Skipp said:
They use those, well something like those at work…they swear by them….they have a tool allowance too….trying to get my maintenance buddy to “loose” his….he’s a tight bastard….
Click to expand...
Ooooh I thot I was the only one with one of them... got a welder buddie that's a real PIA tryin to get him to do something for me.
 
markus

markus

Well-Known Member
#17
#17
I had a 3/8" matco digital wrench, I bought when I was a technician at Toyota and ended up hating it. It didn't click or skip when you got to your setting, instead there were 3 lights, a beep and a readout and you never could match (or at least felt that way) if your were say doing a head or something to that nature. having that click or skip to me was always easier. The other thing was because It was used very infrequently (Toyota engines didn't have much for major mechanical repairs at the time so you weren't using it on a daily basis) I always had problems with the batteries, one time a plastic piece cracked an blew off the back of it, etc... I went back to the clicker type like my 1/4" and 1/2" drive ones are.

I could see if you were using one day in day out repeatedly like on an assembly line etc.. but digital just means more problems.......My digital ac gauges "I just had to have" ended up with the same fate.......traded in on the tool truck for pennies on the dollar for something else :D


 
copyman

copyman

Well-Known Member
#18
#18
Ok, so went to Harbor freight and the $20 torque wrench was rated 50-80 in. lbs, one for a few dollars more went to 100 in lbs. Looked at everyone available and none went to 450 in lbs which is what the spec is for FW nut. Highest rated was 200 in lbs. The one I have goes to 250 in lbs. which I bought on amazon for $50. I use it for every bolt on the engines except the FW. Now that I think about it when I was shopping for a torque wrench for first engine I rebuilt I couldn't find one that went that high or was very high price and why I always just tightened with a 1/2 ratchet.
Since this is first engine I didn't time and shearing the keys going to try timing and tighten with ratchet as I always do and see what happens. Worse that can happen is it shears another key.

Like I posted since it looked like the stater bolts were never touched I didn't time this engine. I "assumed" the timing was correct. But think it was Markus on this forum that posted "never assume anything with small engines"

Will report back
 
markus

markus

Well-Known Member
#20
#20
copyman said:
Ok, so went to Harbor freight and the $20 torque wrench was rated 50-80 in. lbs, one for a few dollars more went to 100 in lbs. Looked at everyone available and none went to 450 in lbs which is what the spec is for FW nut. Highest rated was 200 in lbs. The one I have goes to 250 in lbs. which I bought on amazon for $50. I use it for every bolt on the engines except the FW. Now that I think about it when I was shopping for a torque wrench for first engine I rebuilt I couldn't find one that went that high or was very high price and why I always just tightened with a 1/2 ratchet.
Since this is first engine I didn't time and shearing the keys going to try timing and tighten with ratchet as I always do and see what happens. Worse that can happen is it shears another key.

Like I posted since it looked like the stater bolts were never touched I didn't time this engine. I "assumed" the timing was correct. But think it was Markus on this forum that posted "never assume anything with small engines"

Will report back
Click to expand...
they are in Ft. lbs ( and Nm.) not In. lbs when you get into larger headed torque wrenches. Ask google to show you the difference between them, and how to convert if needed, Then look in your book at the torque settings page, as they will usually show all three, also be sure to follow the x to your specific engine and flywheel style on that chart as they vary depending on size and type of wheel.
 
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