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Discussion Starter · #1 ·
Hello all! New here, and sorry but this will be a long post.

Long story short, the engine is toast and it's getting a new one, pending delivery on Tuesday. Part operator error, part seller ignorance. Probably mostly operator error.

Let's start at the beginning. About a year and a half ago I picked up a 1967 Simplicity Broadmoor 707 from an old gent. He's an old Italian guy in his 70's and was the second owner of the machine. It's been repainted for sure, but I'm not sure what else was done. First owner passed away in the early 90's and gave it to the old Italian, but he didn't use it as he had 4 other mowers/tractors. I picked it up off him for $400 with mower deck, 36" snow blower attachment, a dozer/plow blade, and tire chains. When I picked it up, he started it up and drove it around his driveway to show it was in good working order. It did and didn't smoke, so I was satisfied and I loaded it up and was on my way. Before I left, he mentioned he thought he overfilled the oil. I checked the "dipstick" and saw oil was all the way to the top. I figured it'd either burn off or I'd drain some after I got home.

Fast forward about an hour and a half (how far I had to haul it). I started it, drove it off the trailer, and decided to drive it around and attempt to mow parts of my lawn (I was excited to see how it would cut!). After about 5 minutes, it started shooting out blue smoke. I thought it was the excess oil burning off and kept going. Eventually shut off and wouldn't start again, so I pulled her into my shop and tried to figure out what was wrong. Turns out the piston seized. I checked the oil and there was none! I sat there trying to figure out how it lost that much oil in 5 minutes, because it couldn't have all burned off in that time. Looked at the trailer and there were new oil spots (the trailer had a lot of fluid spots on it). It must've leaked out on the way home and I missed them.

Went through the process of un-seizing the piston carefully, and there was some light scoring (as to be expected) but I've seen worse. The rings looked good and weren't cracked, and there wasn't much I could do to a 50 year old engine anyway and I couldn't find a short block to replace it, so I oiled it and put it back together. Started fine, ran fine, it cut grass fine (never did heavy cutting) so I didn't think much of it. Winter came around and I put the blower on. Chicago winters are hit or miss, usually hit. First few snows of 6" or less were fine. After the snow got wetter and heavier, I noticed it bogged down to the point of dying. Kept running it all winter like that. Something didn't seem right though, so I did a compression test, and turned out it was only pumping out 25PSI! What a champ for hauling an 800lb tractor with my 200lb fat butt through a Chicago winter. Pictures below are of what the cylinder looked like when I took it apart. Anyway, since I still couldn't find a short block, I honed the cylinder and replaced the rings, hoping to regain some compression to keep her going. Turns out I was wrong, as it only made the problem worse. Now it wouldn't start at all. Didn't even sound like it wanted to start.

I decided repowering it was the next best option. The engine model is a 7HP 171701-0120. Best replacement for it is a 10.5HP 215802-0015, and the dimensions aren't an exact fit, but the bolt pattern and shaft size is the same. That engine I found for $600 (plus tax and shipping, adding over $100). I decided to keep looking around. Turns out 215000's replacement was 219907-3029, but that model was discontinued. 219907-3029's replacement is a 21R707-0011, which is still a 10.5 HP and same bolt pattern and shaft size. I ended up ordering that one for $450 shipped as it was cheaper than the 215000 series and it technically should fit like the 215000 series, which was the recommended replacement.

So, I already know it won't be a perfect fit. The bolt pattern is the same, but some of the new engines' overall dimensions are slightly larger (by 1-2 inches). I'm prepared to move/fabricate what's needed. The engine comes with the muffler, but no fuel tank. That's OK because I already have the original fuel tank even though it'll probably need to be moved.

My question: I think it'll be fine, but will the belts/pulleys/trans handle the HP increase alright? Are there any other problems you guys can foresee? Any other advice?

Thanks for reading, and sorry it was such a long post! Morale of the story: check your oil every time you sit on the machine
 

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That Simplicity looks to be in fine shape, except for the engine. Are you certain you need to go that large with your replacement engine? I took a quick look at the Briggs and Stratton site and I see that there is no selection of engines in the same horse power range for riding mowers as the old one you are replacing, but I think it might not hurt to look into some of the engines they offer for the walk behind mowers. The torque values and other specs might work for you, be smaller in size and work better because of more modern design than the old side valve you're replacing.

Maybe somebody else here would have a better idea on that than me.
 

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Thanks for the longgggg post! I get the morale! I made the new owner mistake of leaving the dipstick just hanging in there my first run out of the gate.... Being cautious to check it but getting distracted and in the process half the oil spitting out of the lawn mower! Way to go me! :soap:

I wish you luck on your journey to find a good replacement engine for that fine machine! You will have some experienced guys check in and guide you. Keep us posted on your progress! Oh! And thanks again for the pictures! :pics:
 

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Discussion Starter · #4 ·
Bwdbrn1, that is a good idea, and you're right. It doesn't hurt to look. The reason I never gave a walk behind engine much thought originally was for a few reasons.

Number 1 being the shaft size. Most of the walk behind mower engines I've seen are 7/8" and occasionally a 25mm which is slightly smaller than 1" (although I'm not sure if 25mm and 1" shaft sizes are interchangeable). Not positive on bolting pattern either, but I would imagine it being smaller due to the engines smaller overall dimensions, and there's not much room to drill a tighter pattern because of the cutout for the pulleys.

Number 2, from a longevity standpoint, I'd rather put a larger engine under a lighter constant load than a smaller engine under constant heavy load, but I'm sure that's a debatable topic. I sent the original engine number to a repower specialty site because the B&S site turned up nothing. They gave me a couple of options, most were 10.5 HP but they also gave a 17HP Honda recommendation....... Seems like 10.5 HP was the smallest they get until the 5 and 6 horse walk behinds.

Like I said, that was just my knee jerk reaction, but I'm going to do more research. It would be nice to have something that fits without modification. Thank you for the insight!

And don't worry, as the project progresses, there will be plenty more pictures posted!
 

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I don't believe the higher power engines would be a problem for the rest of the mechanics of the tractor. Going from the little 7 or 8 HP to a 17 HP would be quite a jump and your snowblower would probably toss what ever snow you get from your house to the one at the far end of the block and beyond!

I know you want a working tractor, but something else to possibly consider is the restoration factor. There are most likely Simplicity purists who would gasp at your notion of putting anything other than an original engine back into your tractor.

Here's a couple of sites that might help you with getting your 707 back up and running before the snow falls.

http://www.simpletractors.com/

Simplicity & Allis-Chalmers Garden Tractor Club, Inc.
 
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