Adventures In Engine Rebuilding

[BrianP]

So, how is it that a perfectly sane (other than being a tractor nut), mechanically savvy person embarks on the completely loony odyssey of rebuilding the engine for his father-in-law’s supposedly disposable (Murray) lawn tractor? Good question, glad you asked. You see, the aforementioned father-in-law has this nice little Simplicity 727 with a dozer blade and chains that he brought down from New Jersey. And hey, if I do him this little favor, the cute little 727 (which runs just great mind you), can be all mine. Hmm, okay, I’ll do it. As the saying goes, famous last words. Anyway, I thought that rebuilding the engine of this Murray (no, that’s not a type-o) might be a good little overview for anyone out there with similar desires, who is determined to save a machine they love. Along the way, I encountered quite a few little bumps in the road that I thought I would make good reading over a cup of coffee. Hopefully you will be entertained and maybe even pick up a tip or two along the way. I realized what I was in for, when my father-in-law casually mentioned that he’d overheated the tractor and it started knocking. Hmm, I see. I was further informed that he’d taken it to the local mower shop where they’d replaced the head gasket. I didn’t think to ask how much he got soaked for this “repair” but having already volunteered my talents for this project, there was no turning back. Damn the torpedoes full steam ahead. For those of you who may idly wonder just what happens when you overheat a small engine of the all aluminum variety, I present the following evidence for your perusal. One Briggs and Stratton 12-HP vertical shaft engine. . . Ouch.

Here, you can see the heavy gouge in cylinder wall from the piston rings. By the way, just how does replacing a head gasket fix an engine knock anyway? Uh, you sure you want to do this Dad? Of course, what a dumb question. Once it was decided that the engine would be a good candidate for a re-bore and the insertion of a cast iron sleeve, the project could commence. Whenever tackling a project of this magnitude, organization is the key to a successful rebuild. Here you can see the engine completely dismantled and sitting on my workbench. This part was actually kind of fun.

The hardest part of this whole operation was not finding someone willing to do the work, that turned out to be duck soup. The hard part was trying to get my block back after two months of it being at the machine shop. After several shops desperately tried to sell me a whole new engine, (nope, father-in-law wasn’t interested), I selected an independent shop not far from where I work in Greer SC. I figured I could drop it off after work one day and when it was finished, pick it up the same way. At least that was the plan going in. The guy who ran the shop was pleasant and told me that yes, they do machine work but that it might take a couple of weeks since this was summertime, their peak season. Okay, no problem I dropped off my block and went on my way. My own job kept me hopping so when I stopped in four weeks later, I was hoping I might have gotten lucky and they’d have finished my engine. Nope, the owner wasn’t in, so his wife said she would have him call me. You guessed it, no phone call was forthcoming. Two weeks later, I stopped in again and spoke with one of the shop guys who tried to call the machine shop and got no answer. I made sure he had my home phone and work phone and left the shop again with the promise of a phone call to let me know where things stood. I knew their phone worked, I’d called them several times in the interim but had gotten nowhere. A week later I stopped by to once again inquire of my engine. This time I actually got to speak with the owner once again. He looked up my information on his computer terminal and discovered (well whaddya know), that the reason the machine shop hadn’t finished the job, was (drum roll please), because they didn’t have the model and serial numbers to tell them the specs of the proper bore piston and rings to use. Is that a fact? I then proceeded to inform him that I had indeed given them all the numbers that were on the engine shroud when I dropped off the block, now seven weeks ago. Wait! Stop the presses! Here’s the problem . . . evidently when I dropped off the engine, my serial number had not been entered into the proper field on their work order. He apologized and I said that’s okay, these things happen and I left. Week eight arrived. This time I walked into his shop with a full head of steam. Either I was getting my engine, he was telling me where his machine shop was and I’d go there and get my engine, or I’d call the local police and press charges for fraud, bunko and anything else I could think of. Now I’m as patient as the next guy, but boy, I was worked up into a fine lather. Naturally, he smiled, reached behind the counter and produced my freshly bored and honed block, the gasket set I’d ordered and a new piston and ring set. Now I realized going in that they did not do rush jobs, but in 8 weeks I could have smelted my own aluminum ingots and cast a whole new engine for myself and been ahead of the game. Okay, not really, but you get the point. Where was I? Okay, time to focus on the project at hand. So 2 months have gone by and finally reassembly is upon me. I know what I’m doing right . . . right? Issues with the shop owner aside, the machine shop at least appeared to know their stuff. The block looked factory fresh and I decided to document the process just in case any other members decide to tackle such a project. It is in fact really straight forward, my biggest hurdle was my rather fuzzy memory when it came to remembering just where exactly each part went in relationship to the others. Next time I’ll document the disassembly process with photos too. Oh well, live and learn. In this picture taken of the lower cylinder, you can easily see the two different metals.

Another view, from the top:

The first step was to install the new piston onto the existing connecting rod. I had examined the rod and crank visually and they seemed fine. I committed my first sin by using the old wrist pin, then redeemed myself by installing the new (supplied) wrist pin clips. Repair manuals you see, are strict little tomes. There is never hint of “try this and if that doesn’t work then try this.” They are sprinkled with dire warnings regarding every transgression from the sin of re-using the wrist pin clips (not guilty) to the sin of reusing every component from rings to rods and beyond. Uh, guilty as charged your honor. Penalties are left to the imagination. In the end, I didn’t really sin too much. Really. Next came the first real hurdle, installation of the new rings onto the new piston. Having broken a set the last time I rebuilt an engine, I discovered that there is a special tool made by Briggs and Stratton for just this purpose. Boy, now I’m a professional engine rebuilder Dad!

The only problem was, as many times as I had the rings on and off the piston, using this tool got to be a real hassle, so I tossed it into my tool box a $7.00 expense that may some day prove useful. Now why did I put the rings on so many times? Well you see there’s this little matter of checking the ring end gap to deal with. You’d think that with all the small engine and tractor manuals cluttering my shelves, this would be a snap to take care of. That wasn’t the case. My Briggs binder, (being geared more towards the 23-D in my older Simplicities), proved to be little if any help at all in my rebuilding process.

This one, an old favorite from when I was 13 or so,

gave me a rule of thumb that the ring gap should be 0.002 in. per inch of cylinder bore diameter. Okay that’s nice, but somewhere there’s got to be a spec on this. Doesn’t there? Finally, these two proved to be the most help, the Briggs with assembly and torque specifications, and the small tractor service manual finally stating end gap on new rings should be: 0.010 – 0.018. I still don’t know why it was so hard to find those numbers, sheesh!

Of course I went through two sets of rings in the process. How in heaven’s name did I manage that? Glad you asked, allow me to elaborate. You see, on my first set of rings, I made the mistake of filing the gap too big at 0.015 on the compression (uppermost on the piston) ring and had to go out and get a new set of rings. My local Simplicity dealer couldn’t help, but put me on to a local parts shop where stepping through their door instantly transported me back to the year 1960 or so. Wow! I hadn’t been in a place like this since I was a kid, strolling into Adler & Sons back in New Jersey with my Dad in the early 70’s. I used to love going there because the ancient proprietor always had what you needed in stock. No matter what you needed, this guy had it. It was incredible, the place had the aromatic scent of ancient gas and oil with a bit of mildew thrown in. An ancient Coke machine hummed away just inside the front window. Sometimes he’d be gone for 20 minutes or so looking for the part you needed, (thinking you would have to special order the part this time for sure), when inevitably he’d return from the bowels of his bottomless warehouse, (blowing the dust and cobwebs off the box) and set it down on the counter. Special order a part? Don’t be ridiculous. With good old Adler, you might have to wait while he rummaged through his dusty metal shelves, but he always came up with the needed part. Always! It didn’t matter if it was a belt, a pulley, or a starter, this guy had it. Of course then he’d produce an up-to-date price list and charge you the current price for the part. The shop is long gone now just like my youth, but what an inventory that guy had, amazing! Daydreams aside, I gave the parts man all the numbers from my engine. Now remember, since the numbers off the shroud specified an all aluminum block, the parts man came out with aluminum rings. Okay, how about for a cast iron block? Nope, wrong again. By this point the fellow’s father came over, put on his bifocals and told his son another number to try. Eureka! Just what I needed. Where was I? Ah yes, the $42.00 set of rings, the top ring of which I measured to be 0.011 in. well within spec. No monkey-ing around this time. On with the rings, into the ring compressor device and tap tap tap, down into the fresh bore. Two weekends to install a set of rings . . . ridiculous! Here’s a shot of my third attempt at installing the piston and rod assembly. Why three attempts? The first time, I somehow managed to get the rod bolts installed, only to discover I had them in backwards. Yeah, yeah, laugh if you will, but in this picture you can see a relief cut in the block.

Just imagine the bolt head where the threads are showing. Tight tolerances huh? When I turned the rod around the right way, then the notch on the piston (which my manual helpfully informed me MUST face the flywheel) was facing the wrong way. Sigh! Out with the piston and rod assembly AGAIN, out with the wristpin clips, rotate piston 90 degrees, and re-install wristpin clips. Then, (piston ring compressor tool really earning its keep now), carefully re-install the piston and rod assembly back into the block. Three attempts to install a piston, good thing this is only a hobby for me, I’d go broke if I was in business for myself. As you can see, the third time was the charm.

So far, I was off to a ripping start, only to falter again with the darned crankshaft. Briggs, in its infinite wisdom, developed this thing called Synchro-Balance and it took me awhile to figure out just how to install the oscillating counterbalance assembly. My first attempt had it flopping around loose. That can’t be right! Object lesson, obviously I was too tired, and it was time to knock off for the day. The next day I doped it out in about 2 minutes. A fresh perspective really helps.

In the above shot you can also see the governor shaft and lever sticking out of the brass bushing at the top of the shot. This must be installed before installing the crank. Don’t ask how I figured that one out, just trust me on this, it has to go in first. Ah, the timing marks. This step is legendary in the annals of engine work. Over the years, I’ve heard many humorous stories about getting the all-important timing marks a tooth or two off. Generally chuckled over between swallows of beer and a slap or two on the back of the new guy who goofed it up, this seems to be a right of passage all of us have gone through at one time or another. On this engine the marks are pretty obvious as seen here.

I was really into it now, my confidence building with each freshly installed part. With the engine upended on a bucket and the crank cover on my bench, I test fitted where the governor assembly needed to go.

All I had to do was mentally flip the cover upside down to get an idea of how the assembly needed to be situated in order to install the crankcase cover. Here, the governor assembly has been placed in proper relationship with the governor shaft lever assembly.

Finally I got to the point where it was time to install the crankcase cover. First I replaced the leaking seal with the brand new one that came in the gasket set I ordered. Following my piston ring expander fiasco, I devised a home-brewed, super-high-tech seal installation tool.

Luckily I installed the seal first, since the lip you see on the shaft would have prevented me from using my Rube Goldberg tool successfully if I’d installed the crankcase cover first. I finally caught my first break, perhaps Murphy had finally left my little shop for greener pastures. My elation was short lived and the assembly process came to a screeching halt again, when it came to installing the crankcase cover. You see, a gasket must be installed to keep the oil inside the block where it belongs. Easy enough concept to absorb. However, when you order a gasket kit, they give you plenty of gaskets. Ever wonder why?

Well, it seems there’s this little matter of crankshaft endplay to be concerned with. Darn my repair-manual-brain and it’s niggling over several thousandths of an inch. It seems the reason for so many gaskets is to enable you to set the right amount of endplay of the crankshaft in relationship to the block. I had no means of measuring this, so I sat back and stared at the engine, every so often checking the end play of the crank. Gee, that seems about right, doesn’t it? The crank movement didn’t seem to be all that much, and besides, only one gasket was in place during the disassembly process. In the end, I had a beer, installed one 0.010 gasket and began torquing down the crankcase cover. Now, as any good mechanic or hobbyist worth his salt knows, torque wrenches are critical in engine assembly and I use mine religiously. Unfortunately for me, someone had been at the engine before me and stripped out one of the crankcase bolts. Murphy had returned once more as evidenced by which bolt just happened to be stripped out. Care to guess which one? If you guessed the last one I applied my wrench to, you win the prize. Figures.

Great, now what. Having repaired stripped out threads a time or two in the past, I knew just what I needed. Years ago (when I first started tinkering with small engines), I discovered a neat little tool designed just for problems like this. The tool in question is a little device known as a Helicoil. It’s a set actually, providing you with the necessary tap, coil like threaded insert and installation tool. These sets aren’t cheap, (about 25 bucks or so), but they fix damaged threads like new. I highly recommend them.

I’ve acquired a few of these sets over the years in differing sizes. But as luck would have it, I never seem to have the size I need on hand. One word of caution though, if you buy a set, make sure you look at the tap itself for the required drill bit size. I made the mistake of looking at the size on the package and ended up making two trips to the local hardware store for the necessary size bit. Actually the Ace Hardware store I patronize also happens to be my local Simplicity dealership. Talk about handy. I’ve become a regular there over the past few years, so an extra trip wasn’t really that much of a burden. I always tend to be rather meticulous when it comes to projects like this, so I went the extra mile to ensure that any metal shavings stayed out of the crankcase. The old masking tape and paper towel trick is an old favorite.

To use the Helicoil, you have to first bore out the hole to the proper size.

The tape wrapped around the drill bit is my primitive depth gauge. Don’t laugh, it works and best of all, it’s cheap. Here’s the freshly bored hole, ready for the next step.

Next, I had to tap out the hole with the included tap. It pays to take your time here, since you want the threads to be as perpendicular to the gasket surface as possible.

Next, it was time to insert the actual Helicoil itself with the special tool provided.

All done. Looks like new, works like new.

So, back on with the crankcase cover, carefully re-torquing all the bolts, sweating bullets while doing so. This time my luck held, and so did all the bolts.

With the crank safely installed it was now time to play with the valves. Briggs and Stratton makes a special tool for this too, but after my ring expander tool fiasco, I decided to see if my automotive-style valve spring remover would do. As it turned out it worked just fine. By the way, the spackling compound bucket in the background served as my combination engine stand, oil drip catcher.

In this shot you can see that the spring was compressed enough to do the job. The real challenge was coming up next, installation of the valve spring keepers. I discovered there are two types.

Whoever dreamed up this style of valve spring keeper should be uh, seriously reprimanded. I thought up quite a few inventive tortures as I fumbled to install these little babies. A small dab of grease on each half helps glue them to the valve stem. You’ll also find that a screwdriver, a pair of long-nose pliers and a magnetic parts-fetcher tool all come in handy.

Sweat was pouring off once more, hoping the whole time my valve spring compressor didn’t pick that exact moment to loose its grip and send parts flying all over my shop. Thankfully all went well and after the fourth attempt, (getting both halves installed together is a real test of patience), this one was done. Whew! Now here’s the way a valve spring keeper should be designed.

Slide it in, release your valve spring tool, done. Why did they use two different styles of keepers? Who knows. Must be an engineering reason of some sort. With the valve springs situated, and the bottom end buttoned up, it was time to flip the increasingly more assembled, (and heavier) block right side up. Since the top of the shaft is tapered for the flywheel, I was able to install the upper seal after the crankshaft was in place. My improvised tool worked like a champ once more. I was really sailing along at this point.

Here, I’ve just re-installed the alternator for the charging circuit. Magnets on the underneath side of the flywheel complete the charging system.

Along about here, my camera batteries crapped out, but not wanting to loose my momentum I forged ahead. Actually, if you’ve made it this far, the rest is pretty easy. I installed the flywheel, plastic blower assembly and chaff screen all in about 10 minutes. My Sears strap wrench got pressed into service to hold the flywheel as I torqued up the flywheel nut. Next, I had to set the air gap for the armature. In this illustration what I did was place the armature in position and with the bolts finger-tight, slowly rotated the flywheel magnets towards the armature with an ordinary office folder scrap between the two. The magnets drew the armature in tight, I tightened the mounting bolts and turned the flywheel to free the strip of folder material. You can also use an index card. Don’t laugh, I later checked the air gap with a feeler gauge and it was 0.010, perfect.

That’s pretty much it, all I did was bolt the shroud back on, install the carburetor, air cleaner, oil dipstick and muffler and carried the engine out to my shed for re-installation into the Tractor.

Here, I’m charging the battery which had gone flat over the winter prior to test firing.

The engine started right up, smoked for a minute or two at part-throttle as the rings seated and then it was time for a victory lap around the yard. Even though it was the last week in February, and my lawn was pretty much dead grass and scallions, I couldn’t resist making a few passes with the deck engaged to make sure everything was up to snuff. Project complete!

[RayS]

Very nice post.

[TerryZ]

Even though it was a Murray it was still a Briggs Engine8) Excellent documentary with great pics. Great post!

[ambler]

I use a dab of grease on the valve keepers, it sort of sticks them together on the valve shaft.

[TomSchmit]

What an adventure! I imagine you could get faster at all those little details with some practice, but it is clear why a professional rebuild costs so much !

[johnmonkey]

Great story, now you can do a 16hp briggs twin cylinder. I just got one and it is in pieces, I don't even know where to start. JH

[BroadmoorMan]

That was a good 15 minutes of reading. GREAT post. Good job on the engine. Now, do you have a picture of the 727 or did you not get it yet?

[Willy]

Great post,great pix hove you ever thought of making it into a full length move??:D:D It's funny how some projects realy get out of hand.
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[PhanDad]

I agree with all the others. Tremendous post with lots of tips and details. After a week or so in "Talking Tractors", this post should be moved to "Tech Tips" so we can easily find it when (and if) we tackle an engine rebuild project. And..... where are the pics of your 'new' 727, the root cause of your adventure? PS - wish any of my work benches looked like yours.

[jlasater]

This is actually somewhat motivating. I have a horizontal twin Briggs that died over the weekend and I've been dreading tearing into it. Thanks for showing it's not that hard to accomplish!

[BrianP]

Thanks for all the kind words. I got into this as a winter project, and figured some of our less experienced members would find some inspiration in my little story. I agree it should probably go into the tech tips section, but thought more folks might see it here. Some additional things. Yes, I did use a dab of grease as Ambler suggests, but even then the darn things are a challenge to install. The trick is to get the second "wedge" into place without disturbing the first. I last rebuilt an engine (from my 3410, still going strong), back in 1989 under the watchful eye of my Uncle who was a supervisor for a fleet of vehicles for a township back in NJ. He played straw boss, only getting involved if I got stuck...hence the reference to the timing marks! Taking the thing apart again after test-firing to re-time the gears was messy and not really much fun. For those who've inquired about the soon-to-be adopted Simplicity, no I don't have it yet, have to wait for father-in-law to get back in town in a week or two. I'll post pics when I roll it into my shop. She's not too pretty, but she runs and I've always wanted to tackle one of the smaller machines. Being as how my space is limited, it seems a natural. For those who may be wondering about the cost of this little adventure, (outside of the hours spent, which I don't count since this is my relaxation from a stress filled job), I found the actual receipt from the shop that did the work.

As you can see, I spent just about $200 bucks for the machine shop work, piston and rings set (first set of rings that is), and the full gasket set. Not too bad considering the costs of everything these days. Gives you a real appreciation for professional engine rebuilders that's for sure. One last tip is to keep everything as organized as you can. My humble little shop is in one corner of our basement. Even though I have a dehumidifier running, I covered this with one of those cheap plastic drop cloths they sell at most home centers. Both to keep any rust off as well as airborn debris from my wood working projects. Cleanliness really counts.

[jlasater]

Did that engine origionally have an aluminum bore? Or an iron-sleeved one?

[goatfarmer]

Great story! Nice clean workbench, too!

[JP]

Hey Brian, Let us know when you start another.... We want to come over & watch! LOL GREAT Post!

[BrianP]

Actually, this was originally an all-aluminum design, I think they called it a Kool-Bore or some such. Evidently the design was very suceptable to overheating damage and they later went to the I/C design with the cast iron sleeve...which is what I have now. Regarding the work bench, you haven't seen a "long shot" of it. It's an L shaped affair with one half devoted to mechanical work and the other half to electronics work. While the engine was apart, the other half was a cluttered disaster area, where I was converting 2 dead iMac computers into one good computer for my shop. What little space was left was a pile of wrenches, sockets and screwdrivers that had to be sorted through frequently as the project progressed. I was so pressed for space at one point I had a small hunk of plywood on my drill press to extend my space by 12 precious inches or so. Believe it or not, the workbench is still a work in progress. I work on completing it in between all the other things life tosses my way.

[Morris]

I agree, excellent post. I was just going to ask about the machine shop prices when I read your last comments. Just curious, but has anyone priced a full rebuild lately on similar engines? Not just machine shop but the entire thing.

[quantico]

Thank you for a bit of education.... it's been some time since I have done an engine rebuild. I tend to look for a complete used " doner " engine and just wrench the swap... but this was a really great post with excellent pictures. I think you should be quite proud of your ability to stay with a difficult project.

[Marty-MN]

Your right nice reading over coffee, with all the pics and details you could use this one for tech tips.

[andrewk]

quote:

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Originally posted by Morris
I agree, excellent post. I was just going to ask about the machine shop prices when I read your last comments. Just curious, but has anyone priced a full rebuild lately on similar engines? Not just machine shop but the entire thing.

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If my shop did it, it would be 3.5-4 hours labor, plus parts. 65 dollars an hour, thats 260 in labor, plus 200 for the machine work/piston/gaskets, so thats 460. If we had to do a Helicoil, we get about 5 bucks a helicoil, and then thats another .25 hours. so lets just say 20 bucks, so 480. I don't think we would mess with a rebuild without using a new rod, and I don't know prices off the top of my head, but my guess is 40 bucks. Could be outrageously high. So lets figure 520, then add shop supplies($4), envrio fee($4.50), fuel fee($1.50) (we would be running it, and making any adjustments) and sales tax at 7 percent. That makes a subtotal of 530 even with 37.10 in tax, so 567.10. This price is dependent on the price of machine work in the area, and dependent on parts prices being the same there as here. A short block is probably 500 bucks or so, but I am really unsure. I am going in 'blind' here since I don't have the engine book in front of me. We don't typically do rebuilds, as it is never really efficient to do one. I am ok at it, but haven't done near enough to make money at it yet. A lot of shops don't mess with the things that we used to rebuild and fix, since it is cheaper for both the business and the customer sometimes to just replace the part. The advantage of just installing a short block is the factory warranty. This means that if the factory goofed up in building it, then they get to pay for it, and not the business. More incentive to short-block. Thats the 'professional' side of it... you are money ahead, and you did a very nice job on the rebuild. The only thing I would have done differently is replace the governor gear. Looked a little burnt in some places.