MTD Mower with B&S 12.5HP IC Quiet Engine Repair

[GreenT]

Hi,

I’ve recently acquired an old MTD Mower with a B&S 12.5HP IC Quiet Engine, hoping for some help to get it started!

Mower hasn’t run since I’ve owned it. There are definitely issues with some of the wiring for the safety switches, but suspected the primary cause to be a faulty starter motor as when jumped ( bypassing switch wiring issues ) it would just smoke.

I’ve now replaced the starter motor, the new starter no longer smokes, but will only turn over the engine once or twice and then stops.

Replaced the battery for a new one, so whilst it seems like it could be flat battery, think this would be unlikely.

can anyone suggest things that are likely to be the culprit so I can make a bit of a checklist?

I have ordered a spark plug tester which hasn’t arrived yet, so I can test for spark, but even without spark, surely the starter motor would just keep turning the engine over instead of just once or twice?

Not mechanically minded or great with electrics, but if I have a checklist I can google/YouTube to attempt to fix the problem.

all local shops here in the UK are booked up for months so no scope to get a professional to look at it any time soon!

Any advice would be greatly appreciated

 

[bertsmobile1]

Remove the spark plug
If the starter spins the engine without any problems then the Automatic Decompression is not working
The next step is to adjust the valve lash to 0.004"
If the starter still will not spin the engine then it is new cam time
We really need the numbers from the fan housing near the spark plug
Got a feeling that your engine is a side valve .

 

[smalltimerpm]

Make sure you do your check list on all voltage travel also. YouTube Is great on demonstration.

 

[GreenT]

Remove the spark plug
If the starter spins the engine without any problems then the Automatic Decompression is not working
The next step is to adjust the valve lash to 0.004"
If the starter still will not spin the engine then it is new cam time
We really need the numbers from the fan housing near the spark plug
Got a feeling that your engine is a side valve .

Hi,

At work currently, but have a picture of the mower and believe the engine code reads as

model - 286707
Type - 042001
Code - 9308164E
Thanks

 

[GreenT]

@bertsmobile1 hope it’s ok to follow up on this.

removed spark plug, engine spins free as you’d like, so presuming there is a decompression issue as stated.

the engine is indeed side valve as far as I can tell based on the model number. Are you able to point me in the direction of how I can adjust the valve lash? Lots of resources on YouTube that all seem to be for OHV engines. I’m that clueless I can’t even find where I need to adjust, let alone do it!

 

[bertsmobile1]

Being an L head it makes things a lot different
There is no mechanical ACR on the camshaft to fall apart .

There is a funny bump on the exhaust cam to do the decompression when the engine is revolving slowly
Usually with L heads you get the opposite problem, no compression because the exhaust port errodes .
The fact that the engine turnsover without the spark plug means you either have a buggered cam or have accidently installed a spark plug that is too long which is fouling on the inlet valve or the new starter is not up to scratch.
So you are going to need to remove the head to check the cylinder and the carburettor to access the valve chest which is behind the cover behind the carb
There is no adjuster , you cut the valve seat deeper to reduce the valve lash and grind the end off the valve stem it increase it .
Side valve engines are fairly well limited to around 7:1 compression so most startes should be able to spin the mower.
However if you bought a "High energy B & S starter for $ 40 of ebay or amazon then you got a junk starter that will not work.
BEfore you go ripping the engine apart get some jumper leads and jump battery - to the engine then battery + to the + terminal on the starter.
If the engine spins normally then you have bad battery cables .
Repeat this using your car / truck to eliminate a duff battery .