I have a customer�s 2009 John Deere LA115 ride on mower with a 19.5 HP Briggs & Stratton 31P series engine that won�t start.
A few weeks ago the engine wouldn�t idle under 3,000rpm so I cleaned the carby and adjusted it.
Then a week later it came back with a flat battery. The starter solenoid had shorted internally and one of the rubber boots had melted when they tried to crank the engine.
I replaced the solenoid which stopped the short but the starter can�t crank the engine using a fully charged battery.
When turning the engine over by the flywheel screen it builds up much more compression than normal, which points towards a compression release issue.
There is no binding from the drive belts and it spins over perfectly without the spark plug.
It used to run without any abnormal sounds and has just turned over to 300 hours on the meter so hasn�t had a lot of use.
I don�t want to pull down the engine unnecessarily.
Has anyone got any thoughts on what might be wrong?
I would first pull the valve cover and check the clearances. Being an OHV it is possible that valve clearances have open so much that the ACR no longer works. Also while checking and adjusting look for the decompression bump. Usually on these it is on the intake valve. If there you're good. (ACR = Automatic Compression Release)
If the bump is not there then you have a failed ACR on the camshaft. These engine uses 793880 camshaft on which the ACR is a known weak area is prone to sudden failure.
An non-operational ACR cause also be the cause of the starter solenoid and possibility of a damaged starter as the operators will tend to use a larger barttery to jump start these engines. Just a heads up on this.
Of course there is a possibility that a valve has move causing a bent push rod.
Also with this many hours on the engine I would do a leak down test since these also have a head gasket that tends to blow between the cylinder and the push galley. Basically just for peace of mind as this causes the engine to burn oil; sometimes without anyone noticing until after the engine due to no oil in the crankcase.
LRT if you can establish that the camshaft has failed I wonder if you could be able to fit a decomp valve from a Victa would only need a small hole drilled in the head to allow a small pipe to step up to 14mm to hold the valve. I guess that would depend on the customer.
Thanks AVB it was a long shot but if the cam has failed at 300 hours it just reinforces my disgust in Briggs motors. I rebuilt countless numbers of Royal Enfield motors that were made in India and we knew they were junk because they were built in India, but there is no excuse for Briggs to be building rubbish. The Indians didn't know any better, Briggs do or should do.
The 793380 camshaft is definitely a poor design. If Briggs would beef up ACR weight arm pivot area or redesign to a different ACR it solve the problem. As for failing I have seen them to fail on relative new engines ie low hours. I got one here that only had about 30 hrs on it that ACR broke. Under warranty when it failed but customer dragged around for several months before getting into shop and his warranty had expired.
When these fails most customer assume it is a starter problem and buy a non-returnable starter. When customer come in looking for a starter I ask several questions and if I suspect and ACR problem I suggest them to bring in the mower. Most time time it is just valve adjustment but every once a while it is the camshaft.
They so prone to fail, I see several a year, that I keep one on hand at all times for the sake of speedy repairs during the busy season. It is same with the head gaskets. Just a few years ago it was taking me a week to get these parts but I was lucky that one supplier started selling the Briggs parts that has a 2 day delivery window straight out a Briggs warehouse.
As a customer I would be asking the question as to why you would rebuild this motor with a KNOWN dodgey replacement part so you can wait for it to happen again. Bit like rebuilding an Indian built Enfield with Indian manufactured parts, you know IF the part fits it probably won't last long
LRT just make sure you check everything well especially gear teeth on the governor.
I have replaced these cams and the equipment have lasted a long time. I got one engine that is still in use by a customer that I repaired back in 2009 when I started doing these repairs commercially. Considering I repair 100+ Briggs a year a less than 1% failure rate is not bad. I even had a few Honda cams to bit the dust but they don't as explosive as the 793880 cam. Different ways of failing but still is a failure any way you look at it. I had the lobes on some cams to wear completely round, valve guide in OHV head to move, push rods to fall into the crankcase after getting too clearance.
I have more complete failures with hand held 2 cycles. And forget about those hand held 4 cycles that have a separate oil bath; they don't survive sideways and upside down operations.
AVB do you know if this motor is one of the Vanguard motors? This was being discussed a couple of weeks ago here. Hi to All, I just heard a whisper that Walker Mowers Australia have just received a memo from Head Office to remove the Vanguard engines from their MS 18 model and deliver them straight to a scrap dealer for immediate destruction. Paperwork and photos of this to be sent to Head Office on completion. It would be nice to know the reason for this, but one can guess.....
