Detailed Rebuild How-to: Briggs 3hp Cousins

[Dr. Shop Teacher]

Sticking Valve...a Theory

The exhaust valve on the '74 was really caked with carbon build up. When this engine was torn down, I noted the side cover was not very tight and there was oil caked everywhere. It seems the cover on this engine had been off before.

When reassembling, I noticed the exhaust valve spring was canted on the valve. Thinking I hadn't got it on properly, I removed the spring and retainer and tried again. Looked good...I rotated the engine through one revolution and the exhaust valve stayed open, and the spring was canted over again.

So, what I surmise is the correct bolts for the top two side cover location went missing sometime along the way. All of the bolts were the same length--and one bolt bottomed out on forward side of the engine, and the other went too far into the valve spring chamber. The solution was to cut the bolts down 3/8".So smooth valve travel and tight side cover.

 

[Dr. Shop Teacher]

Crankshaft Endplay

This depicts the more complicated way to measure crankshaft endplay. Basically, Briggs sets a minimum and maximum amount of side-to-side travel for the crankshaft. This gets pretty critical the faster the engine is revving, as too much travel may subject the connecting rod to stress it's not designed for (and that's when something detonates). No matter the intended run speed of the engine, too much end play will shorten the life of the engine.

So, easy way (from the 1975 edition): Clamp the engine to a bench or other hard to move surface. Put a pulley or clutch on the engine and secure it to the crank (side cover torqued to spec). On the flywheel side of the engine, use a little muscle and pull out on the flywheel. It should move a tad. Now push the flywheel back in. Take a feeler gauge and measure the gap between the pulley/clutch and the mating surface on the side cover (a rim that surrounds the seal. On this engine anything between 0.005" and 0.010" is acceptable.

Harder way: Use a dial indicator to measure end play. I didn't have a 5/8" clutch (and I wasn't going to put the sleeve back on). Clamp the engine to the worktable, locate the indicator horizontally to the crank (making sure that the probe is not fully extended). Set the indicator to zero, after pulling flywheel away from the engine. Then, push back in and take a measurement.

So, this is it for awhile...Other jobs to get done before the surgeon gets me on Tuesday. Happy Holidays!

 

[buckeye]

I missed that class.:laugh:

Y'all are way advanced. I just grab the crank and move it by hand.
If it moves less than the worst one I have running, good enough.:rolleye

Great work Pete.
How's the backalacca?

 

[Dr. Shop Teacher]

I missed that class.:laugh:

Y'all are way advanced. I just grab the crank and move it by hand.
If it moves less than the worst one I have running, good enough.:rolleyes

Great work Pete.
How's the backalacca?

You physical terrorist...:laugh: you've spent your life making human physical pain into an art form and not studying up on things mechanical. :thumbsup: Just another little obsessive compulsive task. As to the backalacca, I moved funny today and sent the S1 nerve over the top--my left foot twisted into a form technically not possible.:doah:Tuesday is the day....

 

[RobertC]

Glad to hear they got you rescheduled for your surgery Pete.

Good luck again !

 

[buckeye]

You physical terrorist...:laugh: you've spent your life making human physical pain into an art form and not studying up on things mechanical. :thumbsup: Just another little obsessive compulsive task. As to the backalacca, I moved funny today and sent the S1 nerve over the top--my left foot twisted into a form technically not possible.:doah:Tuesday is the day....

Yeah, makes no sense.
I can fix your torn ACL, but danged if I can figure out the end play on a crank.:laugh:

Be thinking of ya Tuesday. Hope all goes well.
They get ya a bone growth stimulator?
Helps the fusion heal.
At least that's what the sales rep says that brings me strawberry milk shakes from Chic filet.

 

[Dr. Shop Teacher]

Glad to hear they got you rescheduled for your surgery Pete.

Good luck again !

Thanks, Robert...I'm ready to get this over with and get back to walking rather than clomping around (mild foot drop) like a horse.

Yeah, makes no sense.
I can fix your torn ACL, but danged if I can figure out the end play on a crank.:laugh:

Be thinking of ya Tuesday. Hope all goes well.
They get ya a bone growth stimulator?
Helps the fusion heal.
At least that's what the sales rep says that brings me strawberry milk shakes from Chic filet.

Thanks, Tom. They had me on a "heavy cream" Ensure-like drink to promote healing that I'll go back on after surgery. No word on a stimulator, yet. Strawberry, eh? I figured you for mint. :laugh::thumbsup:

 

[buckeye]

I'd drink a strawberry milk shake every day.

 

[Dr. Shop Teacher]

I'd drink a strawberry milk shake every day.

Over that vanilla flavored stuff, absolutely!

 

[Dr. Shop Teacher]

Cylinder Head

I actually had this work done before surgery, but ran out of time to post. Installing the cylinder head properly is, obviously, critical to the operational ability of the engine. You'll see, in some threads, people talking about cylinder pressures in small engines. Pressures are notoriously hard to measure in single cylinder engines and require very good measuring gauges.

For my purposes, making sure I had good rings and ring gaps, valves sealing properly and good cylinder measurements is all that is necessary for the foundation of good running engine. One of the first things necessary is to make sure the head bolt threads in the block are clean and free of any residual debris. Ideally, you'd do this in block prep. The easiest way is to run a 5/16-18 tap in each bolt location. The tap breaks loose rust and debris.

A word about head bolts--check them over carefully and if they were really rusty or the bolt head damaged, consider new ones. If you're planning on a "concours" restoration, reusing the originals or locating OEM bolts is a must. If you're resurrecting an engine frequently exposed to harsh weather (like a Tecumseh from a snowblower), it's wise to order a new set of bolts (a trip to the hardware store ain't the place to get the proper bolts). Bolt lengths differ, so get the part number and item count.

Next up is to locate the gasket on the mating surface:

Place the cylinder head on the block...

And insert the bolts. I've started using anti-seize because the bolts are steel and the block is aluminum (and maybe a bolt won't break when removing the head in the future). There is also an extension of the blower housing (shroud) that is placed on the head. Note the three arrows in this picture. The three longest bolts are inserted as the arrows note. It's not intuitive as there are other locations where these same bolts will fit.

Here's the torque sequence for the head bolts. Note the different head shapes have differing torque patterns. Use the one that matches the shape of the head.

A torque wrench is a critical tool to have in the tool chest--You can get a beam torque wrench with a pointer from Sears for about 25 bucks or one from Harbor Freight with a calibrated twist handle for about the same money. Inch-pound torque wrenches are typically 1/4" drive. Foot-pound torque wrenches are typically 3/8" drive.

Head bolts are tightened down just snugged ( a little pressure). Following the torque sequence, bring each head bolt half way (roughly 70 in-lbs), then follow the sequence again and bring the head bolts to 140 in-lbs.

A new (for me) and better-be-fun task is up next...:blink::shrug::blink:

 

[Fantic Freddy]

I'm sitting in your class tonight, how are you feeling?

 

[Dr. Shop Teacher]

I'm sitting in your class tonight, how are you feeling?

Coming along slowly. Want to do more...but my spine says, "no." Thanks for asking!

 

[chipper]

Glad to see you back at it ( at least a little ) Pete !!

 

[Dr. Shop Teacher]

Glad to see you back at it ( at least a little ) Pete !!

Thanks, Ang. Improve a little every day.:thumbsup:

 

[Dr. Shop Teacher]

And, now something completely different: Crank/PTO Bearing Install

The '64 and '74 had plain side covers. I sourced a couple of bare/short blocks a while back to get the side covers and cam from them for these two builds. One cover was a bushing cover and the other a bearing cover. I also needed a crankshaft for the '64 because the stock (bushing) crank PTO was too short for a mini-bike application. So, I needed to blend two engines together to make one good one. Here's the NOS crankshaft as I got it:

The crank bearing was only partially installed (a good thing), so it pulled off fairly easily. Normally, crank bearings get removed with an arbor press (page 10-5 of the current manual), I used a puller to lift it off.

Typically, there are alignment marks for cam timing. I marked mine in red, as OND demonstrated.

With a bearing crankshaft, these two timing marks are not going to be visible.

So an alternate timing mark is made on the counterweight of the crank and a different tooth of the cam. Since I'm using the original cam, I had to identify new alignment marks. This is done by locating the cam properly lined up with the factory timing marks (and in the block). Note the additional factory mark on the below photo:

That additional timing mark is somewhat visible, but not completely. To be sure it's aligned correctly, select a location where the marks will be visible and drill a very shallow divot into the counterweight.

On to installing the bearing. The bearing is not a press fit and has to be heated to slide on to the crankshaft. This is done in a pan of hot oil. The oil should be no more than 250 degrees, and I checked with a thermometer (YOU DON'T WANT IT TO BOIL). I used some cheap 30 wgt oil and a sauce pan to "saute" the bearing. The bearing cannot sit in the bottom of the pan, so I used an old hose clamp to suspend it.

I heated the bearing for about 15 minutes. The manual does not give a time, so give it a best guestimate. Whatever you do, you don't want the oil to burn. After "saute-ing," put a glove on, grab a rag, and a pair of tongs. Pull the bearing out of the oil, and set on a rag or paper towel. Using another rag, grab the crankshaft and pick up the bearing with the other hand and rag.

MAKE SURE THE BEARINGS ARE FACiNG TOWARD YOU (IN THE DIRECTION OF THE SIDE COVER). Slide the bearing into position and let cool.

After the bearing and oil have cooled, clean up the kitchen and open the windows for a few. If you're lucky, your spouse will never know you've made "bearing donuts."

Mine wandered out and asked, "what are you doing?" I simply said, "you don't want to know." She shook her head, grabbed a cup of java and sighed. :shrug::doah::laugh:

 

[Dr. Shop Teacher]

64 Piston, Crankshaft, Cam Install

Plenty of surprises today. I didn't think the bearing crank rod journal would be a different diameter than the bushing crankshaft. Turns out it was, and I was in luck: I had a 3hp rod that fit the new crank. First up was easing the crank and cam into the block. The journals were pre-oiled before I installed. Took a little finagling to get the teeth to line up properly.

Piston came next. I needed to swap out rods and learned a little bit about piston pins. They may be solid or hollow. Had never seen that before but was referenced in the 1975 Manual.

You can see the difference in the rods below. There's also a difference in the pistons, but I'll get to that. You remove one spring clip and drive the pin out. Be sure to maintain the same orientation of the piston to the rod, as the piston and rod must face the flywheel side with the rod cap facing the valve cover. The piston generally has a mark on the pin journal indicating its orientation.

Once the new rod was installed, it was lubed and the piston installed with a ring compressor (shown previously). Rod cap and oil slinger installed along with lock tab. The side cover got a new seal, and is installed so that the seal face is just below the chamfered lip. I used a large socket to drive the seal into place.

Note the difference in the length of the side cover bolts. The shortest typically go in the top two locations but since this is a different style cover, I needed bolts of equal length.

 

[Dr. Shop Teacher]

A little bit about pistons...

I had swapped rods. But I didn't make life easy and just take the piston/rod assembly, install rings and use it. There are two types of pistons and these are not interchangeable. Pistons stamped with an "L" are used only in sleeved blocks.

Those without the "L" stamp are used in Kool Bore blocks. The 64 and 74 are both Kool Bore blocks. The pin journal is also marked. In this particular case, the pin journal is marked "X" and "I," for intake and exhaust. This ensures you orient the piston correctly in the cylinder.

 

[Dr. Shop Teacher]

The 64 is buttoned up

The side cover was torqued to 85 in-lbs. Crankshaft end play is well within limits, so we are ready for final cleaning and prep for painting for both engines. You'll note this is a 5/8" crankshaft. This will be sleeved out to accept a 3/4" 2-speed Max-Torque clutch. Just a hint as to what this engine is for.....

 

[Dr. Shop Teacher]

Drilling PTO Locking Bolt Threads

So, I'm a little daring at times. Rescuing and restoring old engines will generate challenges. Both of the Briggs had crankshafts that were not drilled to accept a PTO locking bolt (typically 5/16-24). I needed to drill these and did so using my table top drill press. Apparently, there is a jig available from OldMiniBikes, but I couldn't find it and customer service wasn't able to either, but they'll call me if they do have it. I'll post the P/N if I get it from OldMiniBikes.

If you do it my way (the difficult way), a lot of time is necessary to get the drill press and the engine level and square on 3 axis (x, y and z). I used several clamps and wooden shims to get it correct, knowing that once the clamps were tightened additional adjustments would be necessary. The first engine took the longest to get lined up, and the second just a bit of time.

After this was done, I used a tap to properly thread the crankshaft(s).

 

[Dr. Shop Teacher]

Valve Cover, Carburetor and Tank Gaskets

The cousins received new gaskets for the valve covers and had the tank/carb assembled. Make sure the remains of old gaskets are removed and the mating surfaces are clean. Valve cover gaskets are simple, and the covers just need to be snugged tightly in place.

I stuff the openings with Painter's Tape to keep dust, etc out and to prevent paint overspray from getting in the engine.

The Carb-to-Tank seal is among the most critical. You want a tight seal, but you don't want to run the risk of warping the tank when attaching to the carb. A previous post describes how to true the carb base. Make sure the mounting screws are nice and clean (especially the threads because they are exposed inside the tank). Line the gasket up, insert the pickup tubes into the correct opening and insert screws. >>Just like torquing the head, the screws should be tightened evenly and gradually: first one part way, then the second part way and third part way.<< Bring each screw down and lightly snug. Then tighten them uniformly. Sadly, there is no guarantee that there won't be a leak (either vacuum or fuel).