1996 B&S 15.5HP engine issue

[gtr1999]

Hi,
I am a new member here and have a Craftsman 42" tractor with the original B&S 15.5 hp engine.
Model #28N707-0173-01
Code # 95121348
I have kept this old machine running since new. We bought it for a small business and once they stopped doing lawn maintenance, I bought the tractor to use at home. All in all it's been a great machine but the other day I fired it up, took it out, there was slight glitch turning over the engine, but it fired up and I used it for a few minutes until it shut down. Dead in the water, spins all day long not binding, nothing. I checked the initial parts and found the coil wire must have had a break in it as the spark was good at the coil but not at the terminal end using a spark tester and spark test pen. I replaced the coil with a new B&S coil and set the gap, checked it for spark and it was complete then. However, it was still dead.

I checked compression using two different testers, both the Shrader vale in place in the tip, and both were about 45 psi. Wet test brought it up to 50 PSI. I didn't have a leak down tester handy to check it.

I jacked it up, pulled the valve cover and found the aluminum intake push rod broken. The plastic rectangular guide was broken as well. The head gasket didn't appear to be blown out in the typical location. The head gasket I replaced several years ago, this was the second one in 30 years.

My questions are
1- It spins free, so is the compression release still good?
2- I pulled the head and didn't get to it yet. I was thinking possibly the seat was damaged possibly being the cause of the lower compression. I don't see any cylinder grooves at all. Smooth. Does this sound reasonable?
3- Is there a direct replacement engine for this tractor and if so doesn't anyone have a model number?
4- I am debating pulling the engine to check the cam or just putting in a new intake push rod and probably a new exhaust rod, hew head gasket, and seeing if it fires up. Why were the intake rods not steel, sacrificial ?

Thank you

 

[ILENGINE]

Intake push rod is aluminum to deal with the different expansion rates of valves and other components. You can use steel for both if you want. It is fairly common for the aluminum push rod to wear through on that plastic guide in some cases. Some will say it is due to lack of maintenance and oil changes and the oil gets abrasive leading to the plastic guide wearing through the rod. I would replace the head gasket, the push rods, and guide plate for starters. Most likely the camshaft ACR is fine. Without the intake opening can cause issues with compression because the cylinder can't refill with air and creates a vacuum effect.

 

[gtr1999]

Intake push rod is aluminum to deal with the different expansion rates of valves and other components. You can use steel for both if you want. It is fairly common for the aluminum push rod to wear through on that plastic guide in some cases. Some will say it is due to lack of maintenance and oil changes and the oil gets abrasive leading to the plastic guide wearing through the rod. I would replace the head gasket, the push rods, and guide plate for starters. Most likely the camshaft ACR is fine. Without the intake opening can cause issues with compression because the cylinder can't refill with air and creates a vacuum effect.

Thank you
That’s what I planned on doing and just moved the tractor to the back of my shop until I get the new parts.
I’ll post a follow up once I get it all sorted

 

[gtr1999]

I was cleaning up the head today and found the exhaust guide is pushed up. It clearly is higher than then the intake and I am assuming this is a common thing. Checking on the repair of tapping a side hole and spotting the guide is something I can certainly do. Does anyone one know what the reference point is, it looks like it should be equal to the surface in the chamber.

There is a broken washer under the intake spring and I can't locate it on any of the parts diagrams on Briggsandstratton.com or Jacks, which looks like the same diagram. Anyone know if it is really needed? it doesn't look like a shim and it just broke apart.

 

[slomo]

Engine sure resembles it was over-heated. When valve guides move around and part start snapping......

Ever clean the cooling fins?

It's a yearly or more often maintenance item in EVERY air cooled engine manual I've seen.

 

[slomo]

Show us pictures of the cooling fins all around the cylinder/s.

 

[sgkent]

exhaust guide looks like it has migrated. Intake could have too. I would replace the head and all the components in it at this age. You have ring wash over the cylinder too. The oil control rings are at the end of their life. It might be less costly to buy a whole replacement engine than start buying parts to rebuild it.

 

[gtr1999]

Show us pictures of the cooling fins all around the cylinder/s.

Yes I would blow off the mower after use. There was some grass down on the left side of the cylinder but overall it was not packed.

 

[gtr1999]

exhaust guide looks like it has migrated. Intake could have too. I would replace the head and all the components in it at this age. You have ring wash over the cylinder too. The oil control rings are at the end of their life. It might be less costly to buy a whole replacement engine than start buying parts to rebuild it.

Yes I agree the guides moved. I actually reached out to B&S to see what the replacement engine is for this one and was told they didn't have one. I would expact there is a replacement but I don't have the cross reference. If it has the same crankshaft, bolt pattern, the rest would be part of the new engine.

 

[ILENGINE]

31R907-0007 might be a possible replacement. Your original engine is supposed to supercede to the 31A607-3026, but that engine isn't showing in the briggs distribution system. and Briggs shows the replacement engine is the same as the original 31A607-3026 engine.