Ariens starter problem

[senecamowermike]

Recently my 46" mower developed an odd starting problem. The starter will no longer take the engine past the compression stroke unless I manually back the engine up to the back side of the compression stroke to give it a running start into the next one. First thought was dead battery. Jumped it from our van, made no difference. Bypassed battery circuit, connected jumper cables to chassis ground & pos pole on starter, no difference, so concluded starter was bad. Replaced starter, no difference. Had battery tested, & it failed, so replaced it, no difference. I can short across solenoid contacts, no difference. Connect directly to starter from external power source, same thing. If I back the engine up manually to the back side of the compression stroke, it gives it enough of a running start that within 2-3 x of doing this the engine starts & runs fine, so it doesn't appear to be that something has changed about compression resistance. I don't know what else is left that could be faulty.


Mike

 

[mechanic mark]

You need to adjust valves, valves too loose means compression release on camshaft not operating properly. Post engine manufacturer as well as all numbers from engine: example for B&S engine: model xxxxxx, type xxxx, trim xx.

 

[senecamowermike]

It's a B & S engine, but I can't seem to get the photo of the model plate to attach. However, if the problem is valve adjustment, I will take it to a mechanic. How would this suddenly be out of adjustment?

Mike

 

[senecamowermike]

And why does it run just fine once I do get it to start?

Mike

 

[bertsmobile1]

There is a little pimple on the cam giving around .001" to .002" lift which is just enough to release compression at low speeds.
At higher speeds the follower just skips over the top of it so it does not decompress.
Even when the valves are too tight, once running the time it holds the valve just not quite closed is so small very little compression leakage occurs.
So your valve train is slowly wearing or just slowly opening up.
From new I find vales need to be adjusted on the first two services, they will then be right for the next 3 or 4 years.
Some thing silly , like extra hard running for an hour or so can cause the valve to go out of adjustment.
the adjusters are a bit on the crude rude & unsophisticated side as well which does not help.
Honda & Kohler both have a better system with the pimple on the cam being connected to a centrifugal bob weight which pops out of the way once the engine is running.

 

[senecamowermike]

Ok, that makes sense. Then is the adjuster located where I could do it myself? And do I just tighten it a hair at a time until the starter will spin the engine?

Mike

 

[bertsmobile1]

Yes and no.

Yes
The valve adjusters on OHV engines sit at the front of the engine under the rocker cover, so pop off the hood undo 4 bolts and they are right there in front of your face.

And No
there is a specific range of clearances . Too little is just as bad as too much. so invest $ 5 in a set of feeler gauges.
Most are set around the .006" to .010" and anything les than .002" will most likely damage the

Side bangers are a different story they are a major job as you need to pull the head off and remove the valves.

So next thing we need is either a photo of the engine or the numbers of your engine.
So we can point you towards the right manual .

 

[senecamowermike]

My model is 331777 type 2372 G5. I found the specs in my owner's manual: Exhaust .005-.007", Intake .003-.006". Valve cover removed, when I back the engine up to the back of the compression stroke, the lower valve is relaxed. I assume this would be the intake valve, since the exhaust valve should be active at this point. If I rotate the engine to the front side of the compression stroke, the upper valve relaxes, which I assume is the exhaust valve, since the intake valve should be active here. In their relaxed positions, I have adjusted each to the smaller gap of the spec range, to allow for wear to slightly enlarge the gap over time. The starter still will not take the engine past the compression stroke. I have not run the engine since adjusting the valves; I've only tested to see if the starter will fully turn it over at this point. Obviously I'm still missing something, but the question also has occurred to me: Why isn't it just designed with a strong enough starter to take it past the compression stroke without compression relief?

Mike

 

[bertsmobile1]

My model is 331777 type 2372 G5. I found the specs in my owner's manual: Exhaust .005-.007", Intake .003-.006". Valve cover removed, when I back the engine up to the back of the compression stroke, the lower valve is relaxed. I assume this would be the intake valve, since the exhaust valve should be active at this point. If I rotate the engine to the front side of the compression stroke, the upper valve relaxes, which I assume is the exhaust valve, since the intake valve should be active here. In their relaxed positions, I have adjusted each to the smaller gap of the spec range, to allow for wear to slightly enlarge the gap over time. The starter still will not take the engine past the compression stroke. I have not run the engine since adjusting the valves; I've only tested to see if the starter will fully turn it over at this point. Obviously I'm still missing something, but the question also has occurred to me: Why isn't it just designed with a strong enough starter to take it past the compression stroke without compression relief?

Mike

Ok,
now you come to the stop, look & listen bit.
Sit in front of your mower with the plug back in the engine and slowly rotate it by hand watching the valves move and listening to the gasses moving around.
you should be able to hear the engine suck in the fuel then feel the engine tighten up as you come towards TDC then slacken a little and you should be able to hear the comprssed casses escaping, sounds like a deep sigh.
Contine to rotate the engine it should go hard again as the remaining fuel is compressed then almost spin itself when it is on the power stroke then feel the resistance caused by the exhaust valve opening. Do this for a dozen or so times till you get the feel of what is going on. You should be able to feel resistance as the valve springs compress, you should feel no resistance as the valve springs relax & push the cam away
This bonding with your engine happens best on a full moon night facing the north naked :laughing::laughing:

Now if you are not getting compression release then you can tighten up the clearence on the exhaust valve a little more but if you get down to .004" and still do not have effective compression release then there is wear beyond the servicable limit in your engine.
Usually the cam will be worn out and will need to be replaced along with the cam followers, these should always be replaced as a set.
Sometines , particularly if the engine has been alllowed to run low on oil, been run for extended periods with oil that is too heavy or too dirty then the cam shaft bush ( hole in the cases most times ) can also be worn oval.

Watch the mvement of the valves they should move smoothly in & out if one moves with a jerky motion then the valve will need attention as a binding valve stem can also stop the starter motor dead in it's tracks but your problem is usually a lack of compression release

 

[senecamowermike]

I wondered about excessive wear, but the mower is only 2-3 yrs old. I've not messed with the speed, so I'm not running it harder than design. Oil level & appearance are good, it doesn't seem there should be a cause for excessive wear. I'll play with the cycle as you describe & make sure I am at TDC, see if I can find .001 or so somewhere.

Mike