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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

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.

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

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

Mike

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.

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

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 .

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

senecamowermike said:

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

Click to expand...

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

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

The proper location to adjust the valves is 1/4" past TDC which would be the start of the power stroke. Both valves will be closed in this position. Set the valves to spec at this time. Then rotate the engine two revolutions, and then recheck the gaps again to make sure they are correct. Then while rotating the flywheel back and forth over the place where the intake valve is closing, just before TDC compression stroke, you should see the intake valve bump off for a short period of time. If there is no bump then most likely the compression release is broken which will require a camshaft change. Since the Briggs also has a flyweight type compression release just like other engine makers.

If you have to go through the trouble to pull the engine, and physically check the compression release on the cam, just replace it while you are in there.

senecamowermike said:

Big snip
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

Click to expand...

Ok it goes like this.
A 500cc single cylinder mower engine to a starter motor is the same a a 2000 cc 4 cylinder car engine.
But the car engine has a ring gear on the flywheel about 18" diameter so the starter has a much greater mechanical advantage than on your mower with a 9 to 10" ring gear on the flywheel.
So to get the engine to spin fast enough you would need a starter about 4 times more powerful that the one fitted now and this cost big dollars or alternatively a reduction gear starter motor, also not cheap.
Now the magic pudding does not exist so to power this substantially bigger starter you will need a bigger battery and to relace the increased power consumed by the starter you will need a much much bigger alternator.
the bigger alternator will gobble a lot more power from the engine so you will either have to leave it there till the battery is nearly topped up before you start to mow or fit a bigger engine, which will need a bigger starter.
And round and round goes the great big wheel.

Vertical shaft motors are about the most price sensative engine on the market and a bigger starter & alternator plus a real full wave rectifryer and solid state regulator will just about double the price of the engine and increase the fuel consumption by 20 to 40 % depending upon how many times you stop & start the engine. The decompression facility adds some thing like $ 20 to the final price.

As an example some of the engineers at ANU did an evaluation of the effect of disconnecting the alternator on their drive to work car, replacing it with some roof mounted solar cells
They reported fuel savings in the order of 30% so several of our bigger delivery companies are currently doing cost benefit determinations and the flexiable solar cells sittin flat on the roofs ar lookig to be quite a good investment

Here is a easy and fool proof way to adjust valves.

Turn the flywheel counterclockwise two times stop when one valve is open and one closed. Adjust the closed valve then repeat for the other valve.

This is a proven method.

This has been done for years.

Sent from my iPhone using LMF

Ok, I have gone back, checked, rechecked, adjusted, etc. The exhaust valve measurement remained unchanged; I did tweak the intake valve adjustment. I can't seem to notice a slight bump of the exhaust valve on the compression stroke, and most importantly, the starter still will not push thru the compression stroke. Indications seem to be that my compression relief is worn away, but I have never seen an engine experience such premature wear. Is that even possible? How long should it take for tho kind of wear to occur?

Mike

Ok, so I've not seen any other replies since my last post. Just to clarify, I bought this mower new 2-3 years ago (haven't yet dug up receipt to confirm exactly when). In your experience, is it possible that the compression relief has already worn off of the camshaft, or is it more likely that I am somehow missing something in valve adjustment?

Mike

senecamowermike said:

Ok, I have gone back, checked, rechecked, adjusted, etc. The exhaust valve measurement remained unchanged; I did tweak the intake valve adjustment. I can't seem to notice a slight bump of the exhaust valve on the compression stroke, and most importantly, the starter still will not push thru the compression stroke. Indications seem to be that my compression relief is worn away, but I have never seen an engine experience such premature wear. Is that even possible? How long should it take for tho kind of wear to occur?

Mike

Click to expand...

How long is a piece of string ?
Depends upon so many things it is not funny.
Like do you mow along slopes ?
did you ever let the engine oil run low ?
How frequently did you change the oil ?
How do you store the engine over winter ?
how long do you mow for ?
What temperatures do you mow in ?
Are you using the right grade of oil for your ambient temperatures ?
Are you using mower oil or car oil , and yes they are different ?
Do you always run @ full throttle and let the govenor decide what speed the engine should run at ?
Was the person who assembled your engine asleep when he made it ?
Where in the batch was your cam & cam followers during the heat treatment process ?
Were the valves accuratly set from new ?
Who did the engine servicing from new ?
Were the correct valve springs fitted ?

I could go on & on & on & on ( some say I already do )

However none of this means diddly squat right now unless you bought the extended warranttee package and have followed the required servicing regime and are going to try a pro-rate warrantee claim.
But to answer the question I would normally expect to see this kind of wear starting at around the 10 to 15 year mark. Or around 500 hrs to 1000 hrs

The good thing is Ariens are a family company and run by Mr Ariens , although I think he is currently down here working on the Bynorm take over .
And as a family company they take quality & reputation very seriously so you might do well to take it to your local Ariend shop, get a written quote & if it is abnornal wear take it up with HO .
Stress how you bought the machine because of the high reputation of the brand & how bitterly dissappointed you are as a Sears would have given better service,, .
Most times they will come to the party with some sort of mutal arrangement, just be nice, cranky never gets you any where.

Some good chuckles here - thanks for the info. The only downside is I don't have a full service Ariens dealer in my town. I do mow a lot of sloping terrain, and I don't have a lawn, but rather a yard, so yes, the engine is generally at full speed. The oil level has always been good; it has never run low. Altho I have mowed 2-3 seasons with this machine, I confess I have not changed the oil, because it looks very good every time I look at it. Therefore it does have the correct type of oil in it unless it was sold to me with the wrong type of oil. I will say that I bought it from my local Home Depot. It's good to hear that my impression of the company is pretty much correct. I had an Ariens 11hp rear engine rider a number of years ago that I think was the best mower I've ever had. I wish that rear engine design was still around. I find this front engine design to be too clunky and top heavy for the hilly terrain I mow. Much of it causes the uphill wheel to break traction if I'm mowing the hills horizontally, so there is actually a fair amount that I have to mow in vertical only passes. My mower does have a hard life, but I would've thought that really is only a challenge for the drive and the deck. If slope makes much difference in wear on the cam shaft, that could be significant. Your comment about where my camshaft was in the hardening process during manufacture sounds like possibly a significant factor as well. I'll see what I can come up with in someone to work with and see if playing the Ariens quality card helps any. Thanks for the info.

Mike

The old flexi float rear engined Ariens was a really good machine, reasonably priced but a few too many engine & deck options which make servicing them a PIA as each combo of engine & deck has a different set of pulleys so naturally a diferent belt. One of the few mowers people actually ask if I have any old ones to sell. The farmers loved them as the eck stuck out a long way & was really thin so it would go unde the bottom fence wire.

The big problem with just about all vertical shaft engines is they have a large flat & shallow sump so when you mow across a slop, all the oil ends up on one side of the engine.
It was a bigger problem with the flat heads that had the paddle wheel slingers because they end up spinning in free air and the top bush can only run or a minute or so without new oil before it seizes.
I have oft thought that was the real reason why they stressed not mowing across slopes & why Kohler was happier to run greater slopes than Briggs ( Kohler have deeper sumps ).
The hard facing on the cams & followers is very very thin as heat treating is very expensive.
Cams are usually sent through a tunnel furnace for the hardening so the ones on the inside get hotter than the ones on the outside so there is a bit of variation.
Followers usually get done in a basket so the ones on the outside get hotter than the ones in the middle and get the faster quench so tend to be at the top end of the specified hardness.

For now about the only thing that will help is to turn the engine by hand to tdc on compression stroke then back it off till you fell the resistance of the inlet spring starting to open and hit the starter from that position ( sort of Le-Mans start and hope you build up enough momentum to push past compression and off you go

That's actually exactly what I do right now to start it.

Mike

looking at the cam for this engine the compression release located at lower section of cam near the gear if it has broken it will not release compression. I am not a mechanic maybe some one with more knowledge can chime in.

As I've continued to process this, it occurs to me that if I replace the camshaft yet continue mowing all my slopes, I may be right back here again in 2-3 years. Any intel on replacing thus engine with one that has a deeper oil sump, or is it possible to keep my engine over-full with oil to prevent the pump losing contact with the oil?

Mike

The two things that go wrong with the compression release on the camshaft is the return spring breaks for the flyweight and doesn't return to rest when the engine is shut off. The other thing is the weight breaks and then you have no compression release, plus the fact you now have shrapnel in the engine block that can cause other problems.

I have never seen a repeat of a broken compression release after replacement though.

The other thing I thought of is the compression release is on the bottom valve on vertical engines which on single cylinder briggs engines would be the intake valve.