A Briggs & Stratton Model FH meets Murphy's Law, but a Wisconsin engine restorer makes amends.
Last spring, my friend Steve Anderson asked if I was interested in restoring a HP Briggs & Stratton Model FH. Since I've never been up-close and personal with one of these old 'vacuum pumps,' I readily agreed, thinking the restoration would make for a nice spring project. As a self-taught machinist (and I still have all of my fingers!), I've read a lot of books and asked a lot of questions. I have several home-built hit-and-miss and Sterling engine models under my belt, so when Steve asked me to restore this little Briggs & Stratton, it was an offer I couldn't refuse.
The Model FH was mostly complete when I took it from Steve. A cursory exam revealed the exhaust valve pushrod and the choke tube were absent, and most of the threaded fasteners were loose. Upon disassembly, I found the oil pump plunger was missing, the gas tank was rust, and the carburetor's mounting flanges were broken.
Steve gave me the original operator's manual and parts list for reference, which claimed the Model FH was equipped with a four-bolt head. But curiously, this engine only has two head bolts, which seemed a little strange to me since the manual and engine should be consistent. I e-mailed Charles Camara of CPC Reproductions, who sells Briggs & Stratton parts, and he told me Briggs & Stratton often used spare castings from the factory on later models, and that the FH's crankcase probably came from a Model FC.
Unsure exactly what to make of this revelation, I happened to read on the Internet that early F series engines had the model and serial number stamped on the crankcase, while later FH models had this information on the brass tag affixed to the shroud. With that in mind I began cleaning up the crankcase, and sure enough I found the engine's serial number, FB3535, stamped there.
Internet information also indicated that early FHs used slanted cylinder fins and a bronze carburetor. This engine has the slanted fins, but the carburetor is made from pot metal. But that wasn't the full extent of things, as this engine also has a 3/16-inch-wide piston ring, and the oil pump plunger is operated directly from an eccentric on the crankshaft, not from a cam follower as my research indicated. These contradictions still perplex me, and make this engine seem as if it were some sort of mix between a Model FC, FB and FH. I like to think of it as a Model FH mutt.
After the age-old routine of degreasing and cleaning the FH's parts with a wire brush, serious restoration began with removing the rust from the base-mounted gas tank. Because the gas tank is nearly inaccessible, I found it impossible to scrape or wire brush all the surfaces, so I resolved to try the electrolysis cleaning process I had learned about on the Internet.
I hadn't tried the electrolysis method before, and I must say it worked very well, albeit fairly slowly since I used a 12-volt battery charger. A 24-volt charger would have sped up the operation considerably while still maintaining a relatively safe open-circuit voltage. Once the rust was gone I coated the entire inside of the tank with some of Lee Pederson's gas tank sealer to prevent any rust from returning any time soon.
The next step in my restoration was to free up the valves and lap them to get a good seal. I had no problem removing the exhaust valve, but the intake valve's stem is peened over to secure the spring washer, so I lapped the intake in place. That made cleanup after lapping more difficult, but it was nothing 1 couldn't handle.
I tackled the broken carburetor flanges next. The flange was broken into two loose pieces on the left side, and on the right side the broken flange piece was missing. I repaired the left side by first super-gluing the two pieces in place. I then connected them to the carburetor by making a fillet on top with JB Weld. On the right side, I drilled, tapped and lock-tighted a 2-56 screw into the flange base, leaving the screw protruding about a -inch to provide extra support in anticipation of my next step. I then carved a flange mold out of a paraffin block to the proper outline and dimensions of the original carburetor base, clamped the carburetor to the mold and filled in the missing flange area with JB Weld. Presto, I now had a new flange that not only looked great, but also worked great.
I replaced the missing oil pump plunger with the shank of a 'Q' drill bit, which provided the desired degree of hardness and finish. I cleaned and adjusted the points, replaced the leaky condenser and deteriorated spark plug wire, and fabricated a new pushrod. The original wrist pin had worked loose at some time in the past and was bent, slightly scoring the cylinder. Luckily, the cylinder didn't appear to be terminally scuffed, so I lightly honed the cylinder wall. Next, I fitted a new wrist pin and then made an ill-advised decision to reassemble the engine with the original piston ring. I didn't know it at the time, but that oversight would later turn into a major headache.
Adding insult to injury, I also challenged Murphy's Law ... and lost! Despite the fact I've never done restorations this way before, I painted the entire engine my favorite color of blue before reassembling it. The weather was nice that day, I thought 'what the heck?' Little did I know that fateful decision would have implicit repercussions. Murphy says that an engine is 73.8 percent less likely to run if it's painted before it's operational. He's right: The engine looked great, but it didn't run.
Breaking Murphy's Law was a bad omen. I encountered a major problem upon re-assembly when the flywheel magnets dragged on the coil pole, inhibiting the engine from turning all the way over. This was apparently the result of slight wear in the crankshaft bushings, which made the crankshaft displace just a bit. I called Richard Reller, a helpful engine buddy I've consulted in the past, and he suggested I sand down the coil pole pieces that were interfering, using Hi-Spot Blue to spot my work. It took a long time, but it worked perfectly and eliminated the interference.
My streak of bad luck continued, however (Murphy, why do you torment us old-engine restorers?). Once the flywheel was functional, the magneto wouldn't produce a single spark. Clnsure of what was the problem, 1 eventually checked the coil and realized the secondary circuit was open. I should have known, but oh well, we grow too soon old and too late smart.
I converted the engine to battery ignition using the existing points and condenser, which resulted in a great spark. But Murphy still wasn't appeased: The engine wouldn't run. The old piston rings resulted in low compression, and a sticky intake valve made the situation worse.
Tired of the cat-and-mouse game I was playing, I completely disassembled the FH again with the determination to do it right. First, I removed the intake valve by grinding off the peened end. The stem was rusty and badly pitted. I substituted an intake valve with the correct stem and head diameter from a similar, later-model Briggs & Stratton. I cut the new stem to the correct length and cross-drilled it to take a cotter pin to retain the FH's original spring. After lapping the new intake valve, it operated as good as new.
Next, I carefully checked the piston. I'm glad I did because the ring-to-land clearance was 0.005-inch on one side and 0.01-inch on the opposite side. The uneven wear was probably the result of the bent wrist pin causing the piston to slightly cock to one side as it worked. To correct this, I chucked the piston dead true and squared up the ring groove. Once accomplished, I needed a piston ring 1/64-inch wider than the original 3/16-inch size.
Another Web site gave me the idea of using two rings together in one groove to achieve the desired width. To get the 13/64-inch width I required I combined a 1/8-inch ring and a 5/64-inch ring in the correct diameter. Additionally, this solution separated the end gaps by 180 degrees.
At this point, I finally got the gumption and confidence to reassemble the FH. But before I made an attempt to start it, I fabricated a short choke tube using copper tubing and fittings and appropriated a shaft and choke plate from an old weed trimmer carburetor, which I secured with nylon cable straps.
After all of the problems I had experienced, I was finally ready to start the Model FH. After one quick shot of starting fluid, the old engine immediately jumped to life on the first try and continued to run smoothly using battery ignition. A little later, I replaced the battery with a good coil. Now the FH runs well in its near-original configuration. 1 say 'near-original' because the purists among us will quickly point out that the muffler is the wrong type, the choke tube isn't exactly correct, and so forth. To this I reply that if an engine looks like a FH and sounds like a FH, it must be a FH - even if it doesn't have all the expected characteristics.
This engine came together thanks to a unique combination of old engine technology, modern Internet information and, best of all, helpful advice from several new-found old-engine enthusiasts that I now count as friends. Despite the restoration's rocky road and my personal run-in with Murphy's Law, I learned a lot and had fun working with an old engine I previously had never encountered. I had to give the engine back to Steve, but the experience will stay with me forever.
Contact engine enthusiast Ken Hollenbeck's at: 607 Cherry wood Lane, Sister Bay, WI 54234; (920) 854-2461.