Tight Crank on New 10HP Briggs Rod

[Go-Rebels]

My twenty year old 10 HP Briggs (205412-0120-E1) threw a rod and I’m in the process of rebuilding the motor with a new rod (694691) and rings. Problem is that the rod tightens onto the crank journal when the con rod bolts are tightened to 50% of spec (spec = 100 in*lb). Below are pics of the rod and journal when I rotate the rod dry with bolts tightened half of spec:



Prior to rebuild I sanded the crank journal using 1000 grit sandpaper and WD40. I don’t believe the failed crank left any aluminum on the journal and the crank surface looked perfect after sanding. I measured the crank diameter at 1.2500 inch using a calibrated Mitutoya caliper having a resolution of 0.0005". Using ID snap gages I measured the ID of the con rod at 1.2495 inch when tightened to spec. Obviously I have an interference condition.

I added two 0.006" paper shims under the ends on the con rod cap and got the rod to spin but that’s not a permanent fix.

Is my con rod out of specification or am I doing something wrong?

What radial clearance should I expect to see? For example, a 0.002" rod gap should yield a rod ID of 1.254".

 

[Go-Rebels]

Interesting spec for a larger INTEK B&S engine shows the crank diameter to be 0.001" under nominal.

 

[Scrubcadet10]

I might be wrong, but do you know your code date?
i ran into this problem once, but it was with the wrist pin end... turns out i had the wrong rod for my code date.. so it may be the right diagram you ordered from and same model #, but the wrong code date specific part...
maybe someone else who has access to that info will be along shortly.

 

[Go-Rebels]

Code: 000817YD

None of the few online sites I checked made a distinction by date code.

 

[ILENGINE]

Briggs shows a crank rod journal dimension of 1.2485

 

[tom3]

I have resized a couple rods over the years, easy to go a bit too far and get it tight. I use a piece of aluminum foil to get the clearance back to spec. Like to have about .001 clear or so on small journals. Rule of thumb is .001 per inch of journal diameter. Cheap foil is thin, good stuff is thicker.

 

[Go-Rebels]

Briggs shows a crank rod journal dimension of 1.2485

Is it practical to try to take off 0.0015 off the diameter of the crank journal using 400 fine emory paper then finish with 1000 grit?

 

[ILENGINE]

Is it practical to try to take off 0.0015 off the diameter of the crank journal using 400 fine emory paper then finish with 1000 grit?

Not really practical because it would be hard to keep it round. The picture with the crank kind of looks like it could still have a small amount of aluminum smear on it thou.

 

[Go-Rebels]

Not really practical because it would be hard to keep it round. The picture with the crank kind of looks like it could still have a small amount of aluminum smear on it thou.

Yes, the pic of the crank journal does have some aluminum on it as i wanted to show the contact marks on the rod and cap as also shown in the other pic. Suffice it to say that it was perfectly clean prior to tightening the cap on the crankshaft and giving it one one rotation when tight.

I've tried to get some 0.002" thick brass shim stock but it is unavailable at any of the auto parts store I've checked including O'Reilly's, Advance Auto and NAPA. Maybe I need to go to a craft store next.

As a trial I will try next to shim the rod cap using some heavy duty aluminum foil as tom3 suggested.

 

[Scrubcadet10]

Oh gosh my mind is slipping. Taryl has some sort of chemical he uses that removes aluminum transfer... aaarhhh gosh i cant remember the name of it...
you know what im talking about IL?

Edit: Hydroclhoric acid. Thats it.