Odd problem with D-400 engine Lawnboy Model 5083

[Two-Stroke]

Now that it's been run for some time (an hour or two -- how many hours?) how much better does if feel if you turn it by hand? If it's improved a lot since that first day then I'd guess the new rings just needed to be run in. It's still not a good sign that it got hot and stiff like that at first -- maybe something was a little off during the re-assembly process.

Anyway -- that's a nice looking old bricktop. Thanks for the photo and good luck. :thumbsup:

 

[Phototone]

Now that it's been run for some time (an hour or two -- how many hours?) how much better does if feel if you turn it by hand? If it's improved a lot since that first day then I'd guess the new rings just needed to be run in. It's still not a good sign that it got hot and stiff like that at first -- maybe something was a little off during the re-assembly process.

Anyway -- that's a nice looking old bricktop. Thanks for the photo and good luck. :thumbsup:

After the first "issue" with the engine getting tight....I switched to a 1:16 ratio of Lawnboy Oil to non-ethanol gas. I have mowed quite a few of my yards now, and the mower feels and acts normal. No binding of the piston. The mower has plenty of power, does not bog down in thick grass. Starts up with 3 or 4 pushes of the primer (I did not rebuild the primer), and runs steady. Since I was using mowers of this style when this mower was new, I can say this feels normal in every way now, based on my past experience. I am reluctant to go back to 1:32 ratio oil use, though. I am not sure exactly when the Model 5083 was made, but I feel it is right in the transition period on the oil ratio change. It has a 2-ring piston, has a sleeve bearing on the bottom of the crankshaft, and a roller bearing on the top. Using a 1:16 ratio oil mix, the mower runs fine, and does not smoke. I did no honing or any other cylinder preparation other than cleaning. I did not replace the piston, just the rings.

 

[LB8210]

What was the end gap of the new rings?

 

[Phototone]

What was the end gap of the new rings?

Sorry, I did not measure that, and it's assembled and running well now, and I cut yards with it. So I'm not taking it apart.

 

[LB8210]

You are running 16to1 mix in a 32to1 motor. The extra oil is masking the problem. Any time the rings are replaced, the end gap has to be checked and rings fitted as needed. LB service manual calls for .005-.015 end gap. When running a motor without enough ring end gap, as the motor warms up to normal operating temperature the rings expand and the ends of the rings butt into each other, then this forces the rings out tight binding against the cylinder wall. This causes increased fiction and results in the motor running hot and over heating making the piston expand and getting tight in the bore. The extra oil will also cause binding and packing of the ring grooves sticking the rings and ports with carbon. The tight rings and carbon will cause cylinder wall scoring. This motor really needs to be taken apart and the end gap of the rings fitted to the proper clearances before it is too late and major damage happens. Also anytime the rings are replaced the cylinder needs to be honed to break the glaze so the new rings will seat properly to have good compression. Not honing the cylinder will keep the rings from never seating.

 

[Phototone]

You are running 16to1 mix in a 32to1 motor. The extra oil is masking the problem. Any time the rings are replaced, the end gap has to be checked and rings fitted as needed. LB service manual calls for .005-.015 end gap. When running a motor without enough ring end gap, as the motor warms up to normal operating temperature the rings expand and the ends of the rings butt into each other, then this forces the rings out tight binding against the cylinder wall. This causes increased fiction and results in the motor running hot and over heating making the piston expand and getting tight in the bore. The extra oil will also cause binding and packing of the ring grooves sticking the rings and ports with carbon. The tight rings and carbon will cause cylinder wall scoring. This motor really needs to be taken apart and the end gap of the rings fitted to the proper clearances before it is too late and major damage happens. Also anytime the rings are replaced the cylinder needs to be honed to break the glaze so the new rings will seat properly to have good compression. Not honing the cylinder will keep the rings from never seating.

Undoubtedly, what you say is true from a perspective of ultimate restoration. Of course, you know that only one set of rings is available for the D series engines. Are you SURE my model is designed for the 32to1 mix? I believe it was made right around the time of transition to 32to1 from 16to1. In any case, I am happy just the way it is. I am not going for a 100 point restoration, as I am using the mower.

 

[LB8210]

Any D model mower with a 2 ring piston has needles at both ends of the rod and is a 32to1 motor. Any motor ( mower, car, truck, etc. ) that you replace rings on as part of the job you have to check ring end gap. You adjust end gap by filing the ends of the ring to fit the bore of the cylinder of the engine, with the proper amount of end gap. This is not just for a 100 point restoration , but a part of the job of any motor rebuild, a required step in the rebuilding process. The rings are not sized to fit any motor off of the shelf right out of the box, all must be fit to the cylinder bore that will vary between motors. Also before sizing the rings the cylinder has to be honed to break the glaze so the new rings will seat and because honing will enlarge the bore which in turn will increase the ring end gap. If the motor is running hot and is tight, you do need to now before damaging this motor.

 

[motoman]

LB Well said and after the end gap filing we'd hand hone a slight radius on the sharp ends of the rings.