Murray 12.5//40

 

Finally found a LT with a briggs opposed twin!   Heard about it at coffee this AM and purchased it when the fellow came home from work.   Just got home with it so I have little idea what condition it is in.  The machine came from another scrapper (not Johnny) at the very reasonable price of $20.

Here is what I do know.  Engine turns and has some compression.  Transaxle shifts in and out of gear.  All the tires are up and the rear 2 have tubes.  One of the original back tires is toast but it came with 5th tire that does hold air.  Throttle cable seems OK but the choke is a patch job that will have to be replaced with OE.  Seat look good.  Missing headlight lense.

Tractor Data Tag

40702X92F

40 inch deck
type 702
made for 92F

Engine Data Tag

42 ci
Series 2
7 - Vertical
0 - Plain bearing non flage mount
7 - 12V Electric Starter

Made in 91

422707 1510 01

Wednesday, April 22, 2015

Dit the initial assessment.   A car battery hooked to the existing dead battery will not start the engine. Cranks too slow.  But jumping directly to the starter will.  Need to see if unhooking the dead battery will allow it to start with the jumper to the battery cables.

Engine starts and runs nicely on carb cleaner.  The plugs look good.   Compression seems good.

Split the carb and cleaned a bit of gunk out but did not go through it.   Cleaned the gas tank and replaced the line and filter.

Found out the hood mounting brackets are missing.  The muffler on the tractor does not exit where there is a cutout in the hood.  Hmmm


Friday, April 24, 2015


The tractor originally came with a 12.5HP single cylinder.   Made a trip to the roll off and one to the car wash today.   The battery will start it sometimes and not others.

Monday, April 27

Flushed the engine with karosene twice and refilled with rotella t.   But even though I was careful to drain the karosene the engine now rattles and I plan to change it again.

Briggs 6HP Mowers

I was asked to fix a broken shroud mounting hole on the mower for a friend.  Of the six or seven unknown mowers I had on had I found 3 with similar if not identical engines.

I used JB Weld to glue a bolt into the broken out hole from the back forming a stud.   Now it was impossible to put the shroud back on because the recoil started and the stud are at right angles.  I drill the rivets and removed the recoil housing.  This allows one to put the shroud on then bolt the recoil to the shroud.  Need to wait till Monday to find hardware to bolt the recoil to the shroud.  Hoping to find speed nuts.

Clogged Breather

I have been hearing about the stuck breather problem but had never seen one till yesterday.   It was interesting.

I had the head off a junked mower to inspect the cylinder bore.   Turning the engine by the flywheel created enough positive pressure in the crankcase forcing large amounts of oil out the lower valve.  Think pump.

There is no way this engine could run as it would instantly foul the plug.    Blowing into the breather cleared the problem.

This is interesting enough that I may make a video.

DYT4000 Engine

After dealing with the loose valve rocker stud the engine acted up again.  Removed the valve cover and that still looked good.

I figured it was time to check the flywheel key and found this.

Now this is problematic!  Makes me wonder what shape the flywheel is in.  So the flywheel gets lapped to the crankshaft and a new key.  May choose to replace the flywheel.

The flywheel is a bit stubborn so I started it with PB Blaster.

Used a 3 leg puller with an air impact the next day and it came right off.

Lapped the flywheel to the crank.  The photo shows that there are some areas that did not contact but it seemed stable so I reassembled it using a used key from another engine.

If you are thinking this does not look too much different than the key it replaced you are right.  The original key could have been reused but it was somewhat deformed and this one was not.

The key serves two purposes.  It aligns the flywheel during assembly. It also serves as a shear pin should the motor stop too suddenly.  But in normal operation the tapered fit between the flywheel and the crank is what holds the flywheel, not the key.

I mowed for a while.  The engine restarted when hot which was good.  The intake may still be a bit loose but it is useable.  But then it backfires now and then when I crank it so I don't know.

Wednesday, April 8, 2015

Took a good look at the head.  The guide plate for the push rods is missing the plastic inserts.   If I had taken a closer look I might have seen this earlier.  Started to make a post asking about the engine and decided to compare the heads first and bang it was obvious !  It shows up real good in this picture.  The buttons on top the valve stems are also missing.  I should have looked a lot harder when I found the bent pushrod.


Maybe I could have just changed the guide plate but I swapped out the entire head.  So lurch now has the head from the 1st 31P777.  I put the valve cover back on which is correct for the engine.  There must be some difference between the blocks as the replacement head came with longer head bolt screws that did not fit.  The heads are also different castings.

I started and ran it for maybe 30 seconds.  Cranks over real nice and did not backfire, throttle response is good.  Did not smoke much but I wiped the oil out of the cylinder that had collected while it was sitting.  Maybe a bad oil control ring.   Going to give it a workout tomorrow.  Maybe drive it up to coffee.

Thursday, April 9, 2015

Ran the tractor up to coffee and back to see if it would fall apart. The people said it was quite loud.  The engine was a bit hard to start on the way home.  Has started well since then.  Installed the bagger and mowed a bit when I got back.  Dumped 3 baskets.   The tube plugged once.  The new bagger hook gasket works well.

Added a set of std piston rings to the "not now list".