Hi There,

Hoping I can get some ideas here of what to try next go get my Craftsman riding mower starting. The engine on it is a Briggs and Stratton 21 HP model 331877. Here's a summary of what it's been doing and what I've tried/checked so far:

First off, when I tried getting it started this spring I remember the starter was turning the engine very well, but it didn't want to start up and after a bit of cranking the battery died. Eventually mower started after jumping it from my car, but it took quite a bit of cranking. But the starter was having no problems turning the engine over. Since the battery was probably around 5 years old I replaced it along with changing the oil, new air filter, new oil filter, and new spark plug.

Now after doing all this the mower has been cranking really slow. Even when jumping from my car. Even with the car engine running and getting ~13.5V at the mower battery terminals. I had some corrosion on the ends of my battery wires which I scrubbed with a wire brush and baking soda. They look like shiny copper now but still it was barely cranking and usually got stuck I think on the compression stroke. I've tried a new starter and still had the same problem.

Next I read about the intake/exhaust valve adjustments that sometimes need to be done for these OHV engines. I tried turning the flywheel by hand and I found that it turned easily for awhile, then I would hit a point where there would be lots of resistance (like I could barely manage to turn the flywheel by hand) and then another similar hard point right after. Then it would turn freely again for awhile and then those same two hard points again. One detail here is that when I manage to turn past these points of high resistance I hear what sounds like air being squeezed out (kind of like from a bicycle pump). Not sure if this this is good or bad, but maybe someone can let me know (like maybe it indicates the compression release is doing its job). So next I took off the spark plug and tried again. The flywheel turned very easily and using just the battery on my mower the starter could turn the engine over easily.

Based on this I opened the valve cover, found the point where I had a bit of slack on the valve rockers, found TDC from there and turned the flywheel clockwise to move the piston 1/4" further. I found there was actually very little or no gap set, so I adjusted to 6 and 4 mils for the intake/exhaust. After closing everything up and putting the spark plug back in it was still the exact same problem, starter getting stuck on those same spots.

Also I've sniffed the oil and no gas smell there. When I changed the oil I put in 1.5 quarts of Castrol SAE 30. Looking back at the manual I think it said it takes something like 1.3 or 1.4 quarts so it may be overfilled a tad - and there may have been a bit of old oil that wouldn't drain but probably not too much. I was trying to go by the dipstick and it was tough to read. But I know I put in exactly 1.5 since I have an extra half quart left over.

And I just wanted to throw in that whenever I get the mower to actually run it seems to run great and starts very quickly once the engine actually turns over. The initial problem I had when it was cranking nicely was probably just that the fuel filter needed changing.

So at this point I'm not really sure what to try next and I'm hoping to get some help/ideas here. Is the flywheel resistance I'm feeling normal? I was under the impression that there's a compression release mechanism that's supposed to make the engine easier to turn at low RPMs. But maybe easy for me and easy for the starter are two different things. Or could it be electrical problems and I'm just not getting enough current to the starter? With all this cranking it wouldn't surprise me if something in the starter circuit got fried (solenoid maybe?). Any ideas on what to test for and how to test it? I've checked the voltage at the starter and it's way low (like ~5V or sometimes less), but that may just because the motor is getting stuck.

Anyway, sorry for the long post but hopefully the details help. Appreciate any help because this mower is driving me nuts.

 

I always check the spark plugs & all the parts that provide the spark first. If the starter is dragging, that's included Then I look at the fuel supply. Usually one of those two things solve the problem. Valve adjustment is usually not part of a hard starting problem unless someone played with it.

 

Yep I'd try the solenoid next loose wires/bad one will cause erratic cranking

 

Ok thanks! Now what's the best way to test the solenoid? I read somewhere you can cross the solenoid contacts with a metal screwdriver to see if it starts - starting would mean a bad solenoid. Would that work? What about disconnecting my starter and connecting my battery directly to the starter with a jumper cable? Is that a worthwhile test if I can't determine the solenoid to be bad?

 

Here's a quick video on how to test it...

http://youtu.be/MsvJMnpQBas

 

Follow this thread:
http://www.doityourself.com/forum/ou...ont-start.html

 

Thanks cheese. Kind of what I was afraid of. I'll take the valve cover off again and have another look and check for the bump from the compression release. Do I need to leave the spark plug in to see this or can I take it out to make the engine easier to turn? Is there a video somewhere of what this looks like when it's working properly? I've never seen it before but would want to be darn sure of the problem before I would take on the project of replacing the camshaft.

Just curious - how big of a job is replacing the camshaft? Is there a guide around somewhere so I can get an idea of whether this is something I could take on myself?

 

I don't know of a video that shows it. Just watch the rocker arm as you turn the engine (removing the plug will make it easier) and you can see the rocker arm move slightly. The push rod will probably rotate just a bit too.

If it's bad, it's an easy job to replace it. Let us know and we'll guide you through it.

 

Ok thanks for the vote of confidence. I'll try to take a look at this when I have time to see if the CR is working and we'll take it from there.

 

Ok I did get the valve cover back off and watched the valves. I saw the definite movements of the intake and exhaust valves. The valve movements were back to back and it seemed like the timing of the valves moving corresponded with the two hard points I was feeling when turning the flywheel by hand. I didn't notice any other valve movement other than that. When in the cycle should I be expecting to see the bump from the CR and which valve should be moving?

I did also look at the starting circuit again. Yesterday I did try jumping the solenoid terminal with the metal shaft of a tool and that caused the starter to jump but it didn't start. I checked the battery voltage and I think it was 12.2V. I was going to try running my jumper cables directly from the battery to the starter motor tonight, but when I checked my battery voltage again tonight it was down to 2.5V. Obviously it wouldn't start. Should my battery be dying that quickly? I know a new battery isn't necessarily a good battery but is it possible I have a ground fault? I also used my multimeter to check the resistance between my positive terminal and the end of the wire coming into my solenoid. Not sure if this is a valid test but but my meter read 0.5 ohms. Isn't that too much?

 

The bottom valve is the one that should move very slightly. I think it's just at the beginning of the compression stroke.

The battery shouldn't die like that, could you have left the key on? .5 ohms is pretty much full continuity... not a problem. There could very well be starting system problems, but if the comp release isn't working, nothing you do will fix it until you repair the CR.

 

Ok I've watched the valves through many cycles now and have not seen the valve move for the compression release. I even tried lightly resting my finger on the exhaust valve to see if I could feel anything. There was nothing other than the two main valve movements. Where do we go from here?

The reason I was asking about the battery cable resistance is that 0.5 ohms would be enough that I wouldn't be able to get any more than about 25 amps through the starter (with battery at 12.5V). Plus the starter motor has resistance of its own (maybe it's negligible), but I haven't measured this and I don't know how much it is in comparison with the cable resistance I measured. Why would I need a battery rated for 200+ cranking amps if I have a resistance in the path to the starter that won't let it put out more than 25 amps? I've also heard that you can't measure the resistance of heavy gauge wires very well with a multimeter and the real test is to measure the voltage drop when you're cranking (which was why I was asking if it was even valid to check this resistance with a multimeter). Of course I had a huge voltage drop when I measured the voltage coming into the starter since the motor was stalled, so maybe I would need to check the voltage drop with the spark plug out and the motor actually turning.

I agree 100% that if the CR isn't working I won't be able to get it started normally. But I'm thinking if I can jump start it right at the starter motor rather than going through the battery cable and solenoid, I might be able to get it to crank hard enough to get it started. Especially since I can get it to start sometimes with a bit of extra resistance in the path. At least I would have a way of getting the mower started until I can replace the camshaft.

 

Personally I think you are chasing gremlins concerning the starting system. Resistance is not only dependent on on the circuit and or connections, but also the engine condition. The compression release on small engines are designed for a reason. Amps are very difficult to measure with out the right equipment and give very little info as far as diagnosing problems.
Remove the spark plug and if the engine spins faster than normal and very easily, I would say your starting circuit is not an issue.
You may be able to start it jumping it from a running vehicle with a healthy battery and charging system, however, this will also put additional strain on your starter.
I agree with cheese and think he has you on the right track and only fix.

 

I agree with taking the plug out to see how well it cranks without it to get a real idea of the starting system condition.

The reason they put the compression release on the engine is because the starter CAN'T turn the engine without it. Jumping directly to the starter does nothing to increase amperage unless you use larger and/or shorter cables with a larger connection point. Jumper cables won't do it. Even then, the starter motor is only capable of performing so much work, and that limit is reached before enough force is created to turn the engine without the CR. If it could do it, they wouldn't have needed a CR in the first place.

If you want to start it up and don't care about consequences, then set the valve clearance to slightly less than zero and run it. You may need a new head after a while, but it will start. Otherwise you need a camshaft.

 

Thanks for all the help. I definitely want to replace the camshaft. Do I need anything besides the camshaft itself in terms of parts? I found the one I need for 65 bucks. Looks like it's the right part and genuine B&S - Amazon.com : Briggs & Stratton 793880 Camshaft Replaces 793583/792681/791942/795102 : Lawn Mower Tune Up Kits : Patio, Lawn & Garden . Looks like it's the camshaft and both tappets. Hopefully it's a good quality part and will last longer than the original. I don't think the original could be more than 5 years old.

Now before I go ahead and pull the trigger on this, how long should I expect this to take? Is it an all day project or a couple of hours? I'm assuming I have to drain the oil, take the whole engine off the mower, remove the flywheel, open the crank case and then replace the old camshaft with the new one (of course making sure to line up the gears and not screw up the timing). Am I missing anything? And will I need any other tools besides sockets/wrenches? I looked at the lug for the flywheel and noticed it's bigger than any wrench/socket I have so I'll at least need to get a tool for that assuming the flywheel needs to come off. Sorry for all the questions but I've never done anything like this before so I want to make sure I'm not biting off more than I can chew.

I probably won't be able to do this until after the 4th since I'll be on vacation for a couple of weeks. In the meantime I'll probably have to mow a couple of times, but jumping from my car I can usually get it started after a few tries. I've noticed on the lowest throttle it's easier to start. Is this just because less fuel is less compression and engine is easier to turn over?

 

BTW to answer about cranking with the plug out - yes I've done that and as I mentioned in my original post it cranks just fine without the plug.

 

Try and answer most of it.
Cheese will have much more of an idea on how long and depending on how mechanical you are and organized etc.
I disagree with cheese on the premise that the starter will not do the work without the CR. It will since it is a DC motor, however, as I mentioned, it might be detrimental and at least a strain on the starter since the windings are not meant to take the current it requires. It is capable of doing the work however until you let the magic smoke out of some windings/wire....A DC motor is much like a hydro dam, if you have a big enough lake, you can turn anything as long as what you are turning with holds out. Be aware that starters start (last I checked) 120.00 and up.

It is likely you are restricting the fuel/air flow with a lower throttle setting thus requiring less to compress, but could also be an anomaly.... but I am not a train driver so.....

Best of luck and enjoy your vacation.

Azis

 

Pull the engine, leave the top end and flywheel alone. Just remove the oil pan (sump cover) on the bottom. Pull out the old camshaft and lifters, put in the new while aligning the marks, put the governor gear back on the cam, replace the gasket, and button it back up. Mount the engine, re-adjust the valves and crank it up. I can do it in under an hour but for someone not as familiar and without air tools, I would imagine 3 hours would be a gracious plenty.

Azis, the starter might be physically capable, but what will you be left with in the end? It can't handle it. It might a few times, but the first time you have to crank more than a few seconds there will be smoke. That's why they put a comp release on these instead of a 800 CA battery. The more current you run through it, the larger you need the windings, brushes, and commutator segments to be, or heat will build up fast and lead to failure. Now they're cranking up 24 hp engines with the same starter they used to use on the 8hp engines. I guess it's cheaper to make the comp release than it is to make a good strong starter and put a decent battery on it.

I agree with you about there being less air to compress, thus the easier starting at low throttle.

 

 

Ok got it. I'll take a look at how the engine is mounted next chance I get so I can get an idea of how it comes off. I had a chance to look at the service manual for my engine and it looks pretty straightforward once the engine is off. Now you mention replacing the gasket - is that just putting the old one back on or do you recommend getting a new one? It's the crank case gasket? Looks like it would only be like 5 bucks.

 

I rarely if ever re-use gaskets, why do a job twice, do it once do it right the first time and gaskets are cheap.