Detailed Rebuild How-to: Briggs 3hp Cousins

#81
A little more detail on lapping the flywheel to the crankshaft

The images below show the lapping process a little more clearly. This task was particularly important for the 64 Briggs, as it has a new crankshaft. The flywheel was cleaned, rust removed and the magnets were steel-wooled to be sure the Magnetron works properly. Note the uniformity of the mating surfaces.
 
#82
Magnetron (Armature) Air Gap

An important step is setting the armature air gap properly. One common problem with small engines is poor spark, and most often it comes back to a problem with the magneto or coil.

Briggs OEM Magnetrons usually come with a paper card to use to set the air gap between the flywheel and the Magnetron. Aftermarket units do not.

An old trick is to use a business card or a piece of notebook paper folded in half. Yes, I used this method back in the day. Not the way to do it especially if you have a mildly modified 5hp. Briggs sets a range for the armature air gap from 0.006-0.010". I decided to go with 0.008".

Make sure you mount the Magnetron properly with the correct side facing out. Why? Polarity. There's always a tab on the Magnetron to attach a kill switch wire.



I used a feeler gauge to set the air gap. Try to do both legs at the same time. After tightening the screws, recheck the air gap. Most likely, you'll need to make a slight adjustment. Then tighten down pretty hard. There is a torque spec but generally, with a 1/4" drive ratchet, as tight as you can.



Install the debris screen....



Install the shroud (blower housing) and housing extension. Tighten the bolts snugly.



All that's left is spark plug gap, pre-setting the carburetor, hooking up a throttle cable, filling up with oil, a little gas and a test fire.
 
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#83
If you've ever wondered where that shriek comes from when you're revving your older Briggs flathead, this post is for you. Briggs went to a "modern system" some years ago using a ratchet type starter. The starter pawl used on old-style Briggs engines is actually fairly complicated and uses ball bearings as an "on-off" mechanism to rotate the crankshaft to start the engine. Once running the ball bearings release.

The images below show how the pawl is assembled. There are six ball bearings inside the pawl. If the pawl is disassembled for inspection, simply clean up the balls but do not oil. The cover needs to be securely reinstalled, or at speed, it will come off.



There is an oiler hole located at the top of the pawl, as shown below. The manual says to lubricate with one (1) drop of synthetic oil. I'm not too sure why it has to be synthetic, maybe for longer life? Who knows....



Looking from the base up, the inside of the pawl is machined to fit around the crankshaft extension. If you have a crankshaft that DOES NOT have the roughly 2" long extension, you CANNOT use this style starter. A couple of pulls and the pawl will be in pieces without the support crank extension.




This image tries to show the inside of the shaft and the threads. Threads, of course, need to be clean. It is not unusual for the starter pawl threads to pick up some corrosion, dust and dirt, making it more difficult to remove the starter.



So where does the shriek come from? Like everything Briggs does, parts are designed to perform within certain design parameters to make the products they produce cost effective. The starter pawl is NOT designed to handle extended run periods without lubrication and, more importantly, it's not designed for extended periods of revs in excess of 4500 rpm.

Eventually, heat and friction cause the pawl to lock up against the crank extension sounding first as a shriek. It's safeguard is to blow apart sending the ball bearings everywhere.
First I want to complement you on a good write up. I do see one part that I want to comment on though. There should be a small felt washer in the bottom of the starter clutch hole. It is there to hold oil. Also if the oil is dry/stiff on the sides of the shaft where it goes up inside the clutch that is what I always found the "screaming" to be coming from. Cleaning the end of the crank and inside the clutch, followed by lubrication always fixed the trouble.
 
#84
First I want to complement you on a good write up. I do see one part that I want to comment on though. There should be a small felt washer in the bottom of the starter clutch hole. It is there to hold oil. Also if the oil is dry/stiff on the sides of the shaft where it goes up inside the clutch that is what I always found the "screaming" to be coming from. Cleaning the end of the crank and inside the clutch, followed by lubrication always fixed the trouble.
Thanks for the compliment. I hadn't noticed in the current L-head Service Manual about a felt pad to hold the oil. Even my 1974 manual doesn't mention it, so I appreciate you bringing it up.:thumbsup: Need to check the 74 clutch to see if it has the felt pad.
 
#87
Thanks for the compliment. I hadn't noticed in the current L-head Service Manual about a felt pad to hold the oil. Even my 1974 manual doesn't mention it, so I appreciate you bringing it up.:thumbsup: Need to check the 74 clutch to see if it has the felt pad.
Not sure if it is in the manual or not. I have pulled hundred and hundreds of those clutches off, many of them for the screaming you mentioned. There was often the round felt pad inside the hole. Many times it was rotted and just a few fibers left, often times missing. I am 55 now, did most of my small engine work as a teen to early twenties. Funny though, I still have about 10 mowers in my yard and that many more engines in the shed.
 
#88
This is a awesome thread. Thank you Pete.:thumbsup:
Thanks, Karen. I've had fun doing it.

Sticky thread.
Great tutorial.
And looks fantastic.
Tom, some of the gurus probably cringe at some of the things I've done in this thread though I tried to stay true to the service manual. Was really fun decoding the two engines--though just 10 yrs apart, a bunch of differences.

Not sure if it is in the manual or not. I have pulled hundred and hundreds of those clutches off, many of them for the screaming you mentioned. There was often the round felt pad inside the hole. Many times it was rotted and just a few fibers left, often times missing. I am 55 now, did most of my small engine work as a teen to early twenties. Funny though, I still have about 10 mowers in my yard and that many more engines in the shed.
Ah, you're just a young buck:laugh: I turn 58 in April. I taught this stuff years and years ago. We had shelf engines and rarely had to diagnose and correct problems. As I've gotten into this addiction, I have learned a ton about Honda, Briggs and Tecumseh engines in 2 yrs time. I have one clone engine and it's on my tiller.
 
#89
Ah, you're just a young buck:laugh: I turn 58 in April. I taught this stuff years and years ago. We had shelf engines and rarely had to diagnose and correct problems. As I've gotten into this addiction, I have learned a ton about Honda, Briggs and Tecumseh engines in 2 yrs time. I have one clone engine and it's on my tiller.
When I was in high school I spent most of a summer working in a small engine shop (my Dad and I also repaired engines in the garage for about 10 years also). I signed up for auto shop at school, walked in and was told it was actually small engine, not allowed to work on cars till second semester. I told the teacher I was going to drop the class and why. I was promoted to teacher aid.
 
#91
Finishing Up

This thread is coming to a close and I hope it helped some folks with the basics. Like every project, burps, screw ups and busted parts will make life interesting.

The '64 Briggs block ended up being shot and needed to be replaced. Along the way, the recoil spring broke as did the new recoil rope. :doah:The '64 runs well with its "new" older block.

I replaced the recoil spring today and I wish I could offer more helpful hints on how to do so. Couple of points do need to be made: 1) put a dab of grease on the recoil as shown in the photo below. As the rewind spring is wound in, the grease will lubricate it. 2) Another dab of grease should go on the center (pawl) section which faces the starter shroud. AND, 3) THE BIGGEST HINT: The manual does NOT tell you which direction the spring is wound. The spring is WOUND COUNTER-CLOCKWISE looking from the backside of the shroud. Looking at the backside, the spring starts at roughly 2:00 and winds back toward 12:00.



I also installed new recoil ratchet pawls. One had broken open and the infamous squeal was happening periodically even with oil. I did see the felt inserts in the new ones, BTW.





Here are the engines assembled. I've had trouble with the slide on decals sticking to 2K Urethane, so when I masked to protect the shroud when I wrestled the new spring, the decals came off.





 
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