'01 Workhorse 1200G rebuild questions...

[dogdad11]

I've pretty-much reassembled all of the loose parts and got the rebuilt 350cc Robin engine back in the chassis (it literally came to me in several boxes).

And here are my questions...
1) Am I right in seeing that there is no key or anything to keep the clutch assembly from slipping on the engine shaft, with the exception of tightening the big bolt really tight that is threaded into the shaft? Is that all?
2) I can get the starter/gen to turn over by itself, but it's not strong enough to spin the engine when the engine belt is tightened. After rebuilding it, I noticed that I can almost-not turn over the engine by hand, is this normal for this engine?

Thanks!

[BrewCityMusic]

As to #1, yes - the bolt is all that holds the clutch on the tapered shaft. A quick hit with an impact is all that's needed to hold it together, no need for mega-muscle.

With #2, without actually being there it's a hard call to make, weak brushes in the starter/generator can act the way You are describing, as can an engine that wasn't rebuilt correctly. As to the "Tightness" of a 350, you should be able to turn it over by hand on the clutch, but it does have quite a bit of resistance - if I had to venture a guess I would say the starter/gen is the issue - one in good condition puts out a HECK of a lot of torque, so unless the motor was frozen a good S/G should spin it.

If nothing else, a set of brushes will run you $16 and should solve the issue, if not you're only out $16. I'd start there (no pun intended)

[dogdad11]

Thanks for the info.

I was surprised to not see a key on the shaft, but evidently the designers thought we must be pretty strong. So, out comes the impact wrench!

Yeah, my thought was a weak starter too, but when I tried to turn the engine myself, I could only get it to move a fraction of an inch. For comparison, I could move our rebuilt 4-cylinder chipper motor a little better, but then I did have more leverage with the bigger flywheel. With the cart-motor, all I could grab was the clutch assy and as noted it was slipping a little on the shaft. Sure hope I don't have to pull it all apart again!

Wish me luck.

[sccowboy]

When you said "rebuilt" engine, did you just reassemble the engine from the parts that were in the boxes, or did you actually get a rebuild kit and "rebuild" the engine? I'm asking because there are some internal things that could be binding if there were some damage or what not that was not caught. When I rebuilt mine a while back it was tight but not binding and I was able to hand turn the engine over without a ton of force. I would hate to see you have to take the engine back down but if its not right inside and you forcefully spin it over, you will end up back into in anyway. Just a thought. Good luck

[dogdad11]

Good question. Same crankcase and block, but got the rebuild kit and everything else like crankshaft, pistons/rods, camshaft, valves, etc is new, including bored out by 0.025 (or whatever the next bigger size was), because of some scoring on the walls. I lubed everything with STP before assembly and torqued stuff to spec as I went along.

I'll look at it again this week, but I think I'll be back in there like you said. Can't imagine that skinny belt being able to spin the engine the way it is. Thinking of pulling it out of the cart and bolting it all to a bench and troubleshooting it that way. My back can't handle leaning over it as it sits installed. (Besides, can't get enough swing with the hammer to get out my frustrations )

[sccowboy]

Just a thought.... Do you know for sure that the cylinders were bored out to the right specs. Are the pistons stamped with the 25? It really sounds like there is something binding. I have 50 sized pistons and had the machine shop verify the measurements before assembly. It offered a slight resistance when I turned it over by hand but definitely was not hard to turn.

[dogdad11]

Ok, I'm back. And with even-more confusing news.

The pistons are stamped "25", and my assumption is that the shop did bore them 0.025 over (as I requested). I tried one of the old pistons in the holes and there was more play in the bores with it, so I'll have to go with that.

Good News: Pulled everything apart and washed with Marvel Mystery, on the assumption that maybe the STP was too thick and sticky. Put it together temporarily and .. yippeeee!... I could turn it by hand. Bolted on the starter and it spun good... double-yippeee! Opened it all up again to tighten everything to spec-torque before final re-assembly, and hand-turned the crank at each step to be sure all is well.

Bad News: As soon as I tightened the rod-bolts (with pistons/rings/etc in the bores), the crank started binding up again $#%@&!!!!. Pulled the pistons & crank out, re-did the rod-caps and bolts on the crank and tried turning them on the bench. Smooth and easy. Put 'em back in the block... and they bound up once more. BTW, I noticed that the turning-force was a little less when the pistons are at the bottom of their strokes (hmmm???).

Instant Replay: Re-did it once more because I couldn't believe what I'm seeing, and got the same results... No binding anywhere when everything is out of the block, but can't turn crank when installed and rod-caps are tightened. (I think it was Einstein that said "Insanity was doing the same thing repeatedly and expecting different results" ... I'm way past that by now).

Conclusion: Somehow the bores are/got misaligned with the center of the piston stroke, and that's causing the pistons to bind when they are forced into alignment by tightening the rodcaps. I'm thinking that because the crank was a little bit easier to turn when the pistons were at the bottom of their stroke.

Suggestions?

[sccowboy]

Ok....... now for the kicker...... the pistons and rods have a certain direction that they have to face. The service guide specifies the direction. Quote from section D:

With the word “FAN” on the connecting rod oriented
toward the letters “DF” on the top of the piston, slide
the rod onto the end of the wrist pin protruding into
the interior of the piston. Continue pushing the wrist
pin through the piston and into the opposing bore.

It is critical that piston assemblies are
properly oriented and installed in their
original positions on the crankshaft.
A. Remove the cap (ITEM 9) from the PTO (clutch) side
connecting rod (ITEM 10). Apply a coat of assembly
lube to the rod and cap bearing surfaces, and lightly
oil the sides of the piston, rings, (ITEM and cylinder
bore. KEEP LUBRICANT OFF OF THE MATING
SURFACES OF THE ROD AND ROD CAP.
B. Make sure that the piston ring gaps are correctly
positioned on the piston. (DETAIL C)
C. Install a piston ring compressor on the piston, leaving
enough of the piston skirt protruding below the compressor
to start into the cylinder. (DETAIL B)
D. With the word “FAN“, on the connecting rod, oriented
toward the open side of the crankcase, and the
crankshaft at bottom dead center, insert the piston
into the PTO (clutch) side cylinder

If they are not oriented properly then that may explain the binding. If they are oriented properly, I am at a loss on the binding issue but common sense tells me that they are not in perfect alignment and when installed and torqued are not able to turn freely.

Hope that helps.

BTW, if the original pistons were stock and the cylinders have been bored to fit the new oversize pistons, using the old stock sized pistons will not work. The new pistons came with rings that are for those pistons. Verify the cylinder measurement and if you have to, take the service guide with you to the machine shop with the new pistons and block so that your guy can ensure everything will fit correctly.

[dogdad11]

Good point, and one that I tripped over when I did the initial assembly. Altho the old rods had the word FAN on them, the new +0.025 ones did not (our purchasing guy got them thru Nivel Parts). In fact, there was no differentiation on the new rods at all... nothing. Hoping it wasn't an issue, I went ahead with assembly anyways.

When I hit this binding issue, I immediately thought of the FAN thing again. So I reassembled things with the rods aligned both ways. No joy. Also did another assembly with DF and BF on the pistons both ways... still nuttin'


Coincidentally-enough, I have been thinking about getting a new anchor for my boat.

[sccowboy]

How about the crankshaft end play spacer? Did you check the measurements and do the math for it? I'm not entirely sure how much it could effect the the vertical alignment of the crank journals to con rods but you could double check it.