# Intake valve not moving on ST1032 / Tecumseh 10HP



## rpl3000 (Feb 7, 2016)

Hello all. 
I heard a small pop, or snap then the engine stalled. It appears that the intake valve is not moving when I turn the engine by hand. Not sure where to start other than tearing into it and finding out what's broken. I get the feeling that I'm about to explore the bottom end... Any advice or prior experience is appreciated. 

Snowblower: Ariens ST1032 924084 serial# 010536
Engine: Tecumseh HMSK100 159119V (H)


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## Blackfin (Jan 25, 2016)

Camshaft may have snapped mid-shaft. Pull the side over off to check.

Any signs of crankcase damage (bulges, holes etc) in the path of the connecting rod? Wonder if it threw the rod and the rod itself acted as a battering ram and broke the camshaft. Just guessing...


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## classiccat (Mar 1, 2014)

it looks like the spring retainer busted. They're cheap. You'll have to pull the head and remove the valve. While you're in there, it would be a good time to check the valve clearance & reseat the valves. 

was it overrevving when it happened? These valve springs will float above 3600RPM.


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## rpl3000 (Feb 7, 2016)

No signs of crankcase damage, but I haven't seen the bottom. No oil pouring out so that's a plus. 

I just removed the belt cover and the crankshaft appears to still be in one piece. If the exhaust valve is moving then that would indicate that the teeth driving the camshaft are whole. Maybe a lifter?

I don't know small engines but I've dissected many auto motors.


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## rpl3000 (Feb 7, 2016)

classiccat said:


> it looks like the spring retainer busted. They're cheap. You'll have to pull the head and remove the valve. While you're in there, it would be a good time to check the valve clearance & reseat the valves.
> 
> was it overrevving when it happened? These valve springs will float above 3600RPM.


Yep. It was revving high, but then again I don't know the rev spec. I got the machine for free from a friend so I really don't know 'normal operation'. I replaced the carb and set the high idle revs by ear, but it appears I guessed wrong. 

Power while throwing snow was a bit low and I noticed that the muffler was red hot after ~ 15 minutes of running. I understand that can be an exhaust valve problem or a carb tuning issue correct?


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## classiccat (Mar 1, 2014)

rpl3000 said:


> Yep. It was revving high, but then again I don't know the rev spec. I got the machine for free from a friend so I really don't know 'normal operation'. I replaced the carb and set the high idle revs by ear, but it appears I guessed wrong.
> 
> Power while throwing snow was a bit low and I noticed that the muffler was red hot after ~ 15 minutes of running. I understand that can be an exhaust valve problem or a carb tuning issue correct?


3600 is the max RPM measured on a warm engine.

you already have the breather cover off...go ahead and put a feeler gauge in between the lifter & valve stem to measure the clearance (with the piston at TDC)...there's a good chance that it's not closing completely and you're losing compression.


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## skutflut (Oct 16, 2015)

rpl3000 said:


> No signs of crankcase damage, but I haven't seen the bottom. No oil pouring out so that's a plus.
> 
> I just removed the belt cover and the crankshaft appears to still be in one piece. If the exhaust valve is moving then that would indicate that the teeth driving the camshaft are whole. Maybe a lifter?
> 
> I don't know small engines but I've dissected many auto motors.


Look at the bright side, this one only has one cylinder, and two valves, and you can lift it yourself. I can't tell from the picture if something is broken in the valve spring, but if a complete rotation of the crank only operates 1 valve, the it's either camshaft or lifter. Hopefully, any shrapnel from either landed safely in the bottom of the crank case, out of the way and didn't crack the casting where the lifter goes through.

If you have to open the engine, and you find that the problem is not overly expensive (depending on the age and history of the engine) you might as well check the other bits and pieces, such as governor gear, cylinder bore etc to see if there's any other things that need TLC before you bolt it all back together. Don't forget your gasket set.


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## guilateen02 (Nov 23, 2014)

This is what you will be looking at after opening it up. Not to bad if it's just a valve. It could me bent chipped or even fell out after being damaged from over rev, stuck from high temp, valve bounce, etc. You got lucky you can still turn the engine over.


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## rpl3000 (Feb 7, 2016)

any tips to get the crankshaft pulley off? I got one set screw out, but the other one is stuck. Currently soaking with PB blaster.

Is the shaft tapered?


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## classiccat (Mar 1, 2014)

Heat it up using mapp gas and a puller. Just don't fry that crankcase seal.


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## Grunt (Nov 11, 2013)

rpl3000 said:


> Is the shaft tapered?


No, the shaft is straight.


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## ChrisJ (Nov 27, 2014)

classiccat said:


> it looks like the spring retainer busted. They're cheap. You'll have to pull the head and remove the valve. While you're in there, it would be a good time to check the valve clearance & reseat the valves.
> 
> was it overrevving when it happened? These valve springs will float above 3600RPM.




I agree with this.
It looks like the retainer popped off the stem. Personally, I'd leave the bottom alone and pull the head off which is much easier. If you can push the valve down by and you'll see whether or not the cam can move it.

Chances are you either need to reinstall that retainer, or buy a new one. As was already said check the clearances. I did .008" on my intake and .010" on exhaust by removing some material from the end of the valve stems. Before that, I had .006" or a hair less and the machine would have issues after being worked hard. You need to go a hair past top dead center to check the exhaust because of the compression release will hold the valve open a tad until you get past it.

I highly recommend checking your RPM once you have the engine back up and running. 3500-3600 rpm is the most you want to go, below 3500 and the machine will suffer power, above 3600 and you risk blowing something.

I used this to set mine.
670156 Tachometer Treysit Sirometer Vibration Tachometer Tecumseh Tool | eBay


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## Blackfin (Jan 25, 2016)

rpl3000 said:


>


The spring looks visibly compressed in this image. You can also see the tappet poking up and holding the valve open.

If the retainer had failed the valve spring would be expanded to the height of the pocket here.


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## ChrisJ (Nov 27, 2014)

Blackfin said:


> The spring looks visibly compressed in this image. You can also see the tappet poking up and holding the valve open.
> 
> If the retainer had failed the valve spring would be expanded to the height of the pocket here.


He said the intake valve.
The exhaust valve is the one compressed in the image, which is why I think the cam is fine.


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## Blackfin (Jan 25, 2016)

ChrisJ said:


> He said the intake valve.
> The exhaust valve is the one compressed in the image, which is why I think the cam is fine.


Gotchya. Thanks for clearing up what I could have seen had I read a little more carefully :icon_whistling:


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## ChrisJ (Nov 27, 2014)

Blackfin said:


> Gotchya. Thanks for clearing up what I could have seen had I read a little more carefully :icon_whistling:


Over the years I've gained experience at this.
It's been a good 5 or 10 hours since I made that mistake. :wavetowel2:


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## skutflut (Oct 16, 2015)

I thought I was wrong about something once, but I was mistaken...


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## ChrisJ (Nov 27, 2014)

These pictures and video may help

This video shows the method I used to uninstall and reinstall the retainers without a tool. Skip to 11:36 to get to the point.

https://youtu.be/s_R6pUBd818?t=11m36s


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## GoBlowSnow (Sep 4, 2015)

Great info here. And I also agree with Chris. For this 10 HP Tecumseh.. between 3500-3600 RPM. Very critical on this motor. I just made an adjustment on one of my church owned ST1032s that brought it up from 3400 to about 3550 and it was a night and day difference in how the machine responded. I'll be keeping a close eye on this particular machine and am going to purchase a separate Tachometer for it to keep it on there permanently where as i usually just take mine around with me to the various machines I work on, tune it in, and call it good.


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## ChrisJ (Nov 27, 2014)

GoBlowSnow said:


> Great info here. And I also agree with Chris. For this 10 HP Tecumseh.. between 3500-3600 RPM. Very critical on this motor. I just made an adjustment on one of my church owned ST1032s that brought it up from 3400 to about 3550 and it was a night and day difference in how the machine responded. I'll be keeping a close eye on this particular machine and am going to purchase a separate Tachometer for it to keep it on there permanently where as i usually just take mine around with me to the various machines I work on, tune it in, and call it good.


What tach are you considering?
I'd like one for my HMSK80 but not sure what one most guys go with on here.


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## RedOctobyr (Mar 2, 2014)

ChrisJ said:


> What tach are you considering?
> I'd like one for my HMSK80 but not sure what one most guys go with on here.


There was just a good discussion of tach/hour meter options, here: 
http://www.snowblowerforum.com/foru...maintenance-forum/75761-tach-hour-meters.html


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## rpl3000 (Feb 7, 2016)

good news!
I don't know how I missed this the other day but the intake lifter is working! After I removed the intake spring (broken retainer), the lifter fell back down. There must have been a small side load holding it up, that's why I thought it was broken. 

1 - The intake and exhaust valve guides appear to be in different locations. My guess is that when the event happened, the valve guide might have been pushed up. Should I just press if back to the same height as the exhaust valve? or press out and replace. 

Also as I type this, I didn't check if the valve was bent. It looked alright, but I'll chuck it in the drill press and check the runout. 

How's the cylinder bore look? should I try and clean up the top of the piston?


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## rpl3000 (Feb 7, 2016)

Also, a photo of the valves


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## skutflut (Oct 16, 2015)

If possible remove any large carbon deposits from the piston. When they get too thick, they can break off and cause problems. 

I was looking at your photo of the valve cavities and saw something that looks odd, maybe its just the angle of the photo, but whats going on at the end of my red arrow? Is that a hole?


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## rpl3000 (Feb 7, 2016)

skutflut said:


> If possible remove any large carbon deposits from the piston. When they get too thick, they can break off and cause problems.
> 
> I was looking at your photo of the valve cavities and saw something that looks odd, maybe its just the angle of the photo, but whats going on at the end of my red arrow? Is that a hole?


That spot appears normal. I think its just the light.


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## Zedhead (Jan 1, 2016)

Is it just me, or does the intake valve spring retainer look worn/oblong???


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## skutflut (Oct 16, 2015)

I think that's the one that wore out and caused the trouble


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## rpl3000 (Feb 7, 2016)

Yup. Intake valve cap is the broken piece. New one on order. 

I read in the engine manual that the valve guides are permanent (but could be reamed out and replaced). I'm still not so sure that the intake valve guide didn't get pushed up a bit. I think I'm going to leave it alone. Pushing it back might only loosen it up and the valve is moving freely in it. There is quite a bit of play in both valves however.


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## Zedhead (Jan 1, 2016)

Are over sized valves available?


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## rpl3000 (Feb 7, 2016)

Oversized valves were manufactured, but I wasn't able to find any. I took my sweet time repairing this and cleaned up everything. Started the motor today and ran it at idle for about 5 minutes. I still don't have a tach to set the full throttle rpm but i set the governor very low until I get something. I ordered a 3wire Hall effect sensor (10 kHz) from digikey but I couldn't figure out how to read it. I powered it with 5v and use a 0.5kohm pull up resistor but I wasn't getting anything and I got impatient. I had a magnet on my drill press and I was planning on calibrating it with the 3 speed settings. I'm a mechanical engineer and a total hack for anything electrical. I'll have to ask the EEs this week at work what I was doing wrong.
http://m.littelfuse.com/~/media/ele...e_hall_effect_sensors_55100_datasheet.pdf.pdf

Valve clearance were as follows
exhaust 0.15 mm
Intake 0.2 mm 
Spec is .203-.305 mm

The intake is borderline and exhaust is out of spec. I just bolted everything up anyways. Can someone explain why a bit more lift is detrimental?

I also replaced the belts and found out that the auger is stuck on the drive shaft. I had to drill out a shear pin. I figure that I will just run it without pins until it breaks loose.

Is there a how-to with the carb? It seemed I could control the idle speed with the mixture screw and the idle plate screw. I also turned the main jet screw on the bottom of the bowl to stop the high idle surging but I was really was just turning screws and listening.


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## RedOctobyr (Mar 2, 2014)

What was the Hall effect sensor for? To act as a tach? What did you mount it to, and what were you using to read it? I'm also an ME, not an EE. But I'm curious where you could just mount a sensor like that, to get a useful output. 

Let's assume you mounted a magnet somewhere on the flywheel, and the sensor is reading the magnet. I would have speculated it would simply output a different signal every time the magnet passed by. So to figure out RPM from that signal would seem non-trivial, to me. You could figure it out with an oscilloscope connected to the sensor's output, since that would let you figure out the length of time between pulses from the sensor. Then do the math for RPM. Or maybe build some sort of circuit (far beyond what I could figure out) that could measure the time interval, then calculate & display RPM. But it seems to me that you'd need some other "brains" to make the sensor useful. 

I'd buy a ~$10 inductive style tach from eBay and be done with it, the kind where you just wrap the tach wire around the spark plug lead. 

For valve clearances and too much lift, I believe the reason relates to the compression release. The compression release nudges the exhaust valve open slightly during the compression stroke (only at very-low RPMs), to reduce the compression that you have to fight when trying to start the engine. 

But if you have too-little valve clearance, this same nudge from the cam will open the valve further, and you might lose too much compression due to the venting air. You don't want full compression (too hard to pull), but you don't want the compression to be too low either (it won't start). 

The spec may also relate to thermal expansion issues. If you have 0.15mm of clearance, but the valve length grows by 0.18mm during operation, then your exhaust valve won't seat fully once the engine warms up. You'll lose power, it might start running lean which could damage the engine, you might overheat the valve, etc. 

For tuning the carb, you might look in the Tecumseh manuals found as Stickied threads in the Repairs forum: 
Snowblower Repairs and Maintenance Forum - Snowblower Forum : Snow Blower Forums
They might have guidelines for tuning adjustable carbs, maybe at least listing how many turns out to use from fully-closed for initial tuning.


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## rpl3000 (Feb 7, 2016)

I thought that would get a 0-5V output since I was powering it with 5V. I was reading it with a multimeter. It is a bit more than just a switch if you look at the block diagram. There is already a magnet in the flywheel. I was getting a 5V readout when I put a magnet close to the switch and measured the blue and the red wires. I'll post back when I figure it out. I was going to mount it right to the flywheel cover. 

I suppose if I have power problems when it runs warm or after an extended period of time I'll go back in and grind the valves.


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## ChrisJ (Nov 27, 2014)

Too little valve clearance is related the problem I was having, and it has nothing to do with the compression release.

As the valve heats up, the stem expands and gets longer. 0.006" wasn't enough on mine and caused it to run terrible whenever it got good and hot after a while of working. I believe 0.006" is 0.15 MM.

I enlarged my exhaust to 0.010" and intake to 0.008 and have had no problems since.

Your valve lash is WAY too tight on both valves and you will have issues once the engine gets hot, I guarantee it.

Make them 0.20MM for intake and 0.25MM to 0.30MM for exhaust and you'll have no problems.


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## rpl3000 (Feb 7, 2016)

Sounds like I should have had the valves machined...

I wonder if the head gasket I just put in can be saved..... Only one way to find out right?


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