Voltage drops when cranking...

[CraigH]

Hi all, first post as such (apart from my intro) so please bear with me.
I've got abit of knowledge of mowers and engines in general, but this new (to me) mower has me stumped and I don't want to spend anything til I narrow the problem down, this is where I'm hoping someone on here has had a similar problem....

The mower is a John Deere L105 automatic (Briggs and Stratton 14.5 hp intek single cylinder)
I got it given to me with suspected head gasket or rings gone, and it's was over filled with oil aswell.
Since I got it, it's never wanted to turn over properly so I've done a few basic maintenance bits and still no joy....
I've set the armature gap, replaced head gasket, reset tappet clearances (with piston 1/4" down), moved throttle cable as it was set so only ever revved flat out, changed oil, cleaned carb and air filter out, rebuilt starter (mainly to check and see if anything looked amiss).

The problem is still the same though, when I turn the key, the engine turns over about 1/4-1/2 of a revolution then stops dead and the starter starts to buzz....

So I've done some checking/testing and the battery is fine, I've tried another known good battery off my other mower, tried jumping it from my van, cleaned all electrical connections and earth points (I think), all of the above result in the same outcome though.
If I check the voltage (at battery, starter and solenoid) when I turn the key then it drops to 6v.....

So the big question, which is probably blindingly obvious but I can't see it, what do people think could be the problem and where should I start looking next ?
New starter motor maybe?

 

[ILENGINE]

Compression release mechanism on the camshaft is broken and laying in the engine oil sump. Need to replace the camshaft

 

[CraigH]

Thanks for the advice, I'm guessing its a common thing then? Parts don't seem hard to come by and cheap enough.
Is there anything else worth doing while I've got the engine out and all apart? Was thinking of doing rings and obviously gasket set at the same time.
Any pointers for things to look out for or problems I may encounter?

 

[sgkent]

pull the sparkplug and see what it does. Measure the voltages again. If it spins and the voltage looks normal at the battery then the last post is the answer most likely. If it spins but the voltage drops way down then that battery is done for too. Just because a battery works doesn't mean it isn't 90% gone. The other engine can be easier to turn over.

 

[CraigH]

Thanks for the reply. Very good point about the other engine/battery, it's only a 10hp, but that battery was bought brand new for that mower 5 months ago so would assume it's pretty decent still after that little time.
Currently got the 'not cranking so well' battery on a slow charge so will leave it to do it's thing overnight and try it with the plug out tomorrow and see what happens.
I'll report back when I find some more results tomorrow.

 

[RayMcD]

Hi all, first post as such (apart from my intro) so please bear with me.
I've got abit of knowledge of mowers and engines in general, but this new (to me) mower has me stumped and I don't want to spend anything til I narrow the problem down, this is where I'm hoping someone on here has had a similar problem....

The mower is a John Deere L105 automatic (Briggs and Stratton 14.5 hp intek single cylinder)
I got it given to me with suspected head gasket or rings gone, and it's was over filled with oil aswell.
Since I got it, it's never wanted to turn over properly so I've done a few basic maintenance bits and still no joy....
I've set the armature gap, replaced head gasket, reset tappet clearances (with piston 1/4" down), moved throttle cable as it was set so only ever revved flat out, changed oil, cleaned carb and air filter out, rebuilt starter (mainly to check and see if anything looked amiss).

The problem is still the same though, when I turn the key, the engine turns over about 1/4-1/2 of a revolution then stops dead and the starter starts to buzz....

So I've done some checking/testing and the battery is fine, I've tried another known good battery off my other mower, tried jumping it from my van, cleaned all electrical connections and earth points (I think), all of the above result in the same outcome though.
If I check the voltage (at battery, starter and solenoid) when I turn the key then it drops to 6v.....

So the big question, which is probably blindingly obvious but I can't see it, what do people think could be the problem and where should I start looking next ?
New starter motor maybe?

If you have lights pull them on an see if you voltage drops? Or get a clamp on light and do the test. Sounds like you just got a bad battery, load does not make this happen, something would be smoking. If the voltage is dropping you got Zero AMPS to use.. r

 

[slomo]

when I turn the key, the engine turns over about 1/4-1/2 of a revolution then stops dead and the starter starts to buzz....

I would look at the valves again before opening the case up checking on the compression relief. There are 2 TDC strokes on a 4 stroke engine. Could of set valves on wrong stroke. If you are certain valves are proper, cam inspection time.

If I check the voltage (at battery, starter and solenoid) when I turn the key then it drops to 6v

Bad battery and or a flaky ground. Load test the battery at an auto parts store for free.

 

[slomo]

that battery was bought brand new for that mower 5 months ago so would assume it's pretty decent still after that little time.

Most lawn batteries have a 6 month warranty. Just saying....

Got a couple big rig 8D batteries for our work generator. $720.00 for a pair, 6 month warranty from Interstate. WOW.....

 

[StarTech]

And Walmart batteries only have a 90 day warranty and I have seen them fail under warranty.

Starters when partially shorted out or are dragging on the magnets will draw excessive current. I replaced two this year where the owners were tapping in the starters with a hammer knocking the magnets loose. I wish they stop using old automobile tricks. A clamp current meter at the starter will tell if there is a problem with the starter, engine, wiring, or battery.

Troubleshooting electrical problems remotely is very challenging at the best; or at least is for me. I have my own testing procedure which includes voltage drop tests through out the wiring path. I have been working with circuits for over 40 yrs so the tests are pretty well ingrained in me.

 

[CraigH]

Thanksbgor all the replies everyone.
I'm going to go try the battery again in abit, still on charge as I type this.
Electrics are my weak point with cars, etc.... I'm fine if you ask me to rebuild an engine or axle, but for some reason I've always found electronic stuff to be a nightmare.

Got to say, this is a very very good forum with some serious collective knowledge. I'm on a couple of other forums and wouldn't have had half the response in double the time on them!