Export thread

A customer ran his Craftsman lawn tractor without oil. Of course, the connecting rod broke and the crankshaft is not useable. I bought a new connecting rod and a used crankshaft. I've actually tried two different crankshafts and counterweights. I keep having the same problem. The crankshaft timing gear is not flush with the camshaft (shown in the first pic). When I reinstall the sump cover, it puts pressure on the crankshaft timing gear and the engine won't turn. What am I doing wrong? Maybe the piston is turned the wrong way? Please help!!!

Briggs and Stratton engine 31P677-0912-g5 single cylinder
Connecting Rod part #794122
Crankshaft part # 595339

Are you sure the two crankshafts you tried have the same part number as the one you took out? They may look the same, but have different specs. Also, two different crankshafts were used on that engine, what is your code number?

Rivets said:

Are you sure the two crankshafts you tried have the same part number as the one you took out? They may look the same, but have different specs. Also, two different crankshafts were used on that engine, what is your code number?

Click to expand...

120501ZD
the 1 may be a 4.

The date code is 120501
The second pic shows one of the replacement crankshafts on top and and bad one on the bottom. They both have that 352 number, but I don't know what that number means.

Oh, yes, you might be right. The 1 might actually be a 4

Most likely the numbers on the crank are casting numbers, so unless you have the casting codes they mean nothing. Are both the slots on the crank, for the timing gear the same? Do the timing gear align at the same point? Do you have a vernier caliper to measure the thrust surfaces to see if the are the same? Sorry for all the questions, but I’m not standing next to you with a strong drink in hand to see what you have. I’m thinking you may not have matching cranks, or the counterbalance does not match.

Can we confirm that the crankshafts that you have tried are out of an engine with a date code prior to 120701, since there is the possible chance that the used crankshafts are out of an engine after that date code breakdown and create the issue that you are having

Briggs & Stratton Part# 797579 which supercedes to 595339 (which is what the OP said he used) is used BEFORE the date code of 12071800 and he has a date code 120501zd... I think 1205 comes before 1207...
Where did you buy the USED crank from? Ebay?

Scrubcadet10 said:

Briggs & Stratton Part# 797579 which supercedes to 595339 (which is what the OP said he used) is used BEFORE the date code of 12071800 and he has a date code 120501zd... I think 1205 comes before 1207...
Where did you buy the USED crank from? Ebay?

Click to expand...

Makes me wonder if somebody pulled a 596006 but labeled it 595339

The only different between the two crankshafts used that I know of is the flywheel keyway. Briggs change the keyway because flywheel keys being easily sheared. Also the image of the old crankshaft journal doesn't look too bad other than it needs cleaning of the aluminum transfer with Muriatic Acid so that is one option available.

Disconnect the rod any move it out of the way. If the crankshaft now sits lower then the piston rod and piston are incorrectly installed. And check fit of crankshaft afterward by placing the sump cover back on.
It should fully seat without any gaps. Also make sure oil slinger/governor and the counter balance are correctly positioned as either one can jam the engine.

Rivets said:

Most likely the numbers on the crank are casting numbers, so unless you have the casting codes they mean nothing. Are both the slots on the crank, for the timing gear the same? Do the timing gear align at the same point? Do you have a vernier caliper to measure the thrust surfaces to see if the are the same? Sorry for all the questions, but I’m not standing next to you with a strong drink in hand to see what you have. I’m thinking you may not have matching cranks, or the counterbalance does not match.

Click to expand...

The key slots for the timing gear are the same. I do not have calipers to measure anything.

So, here's an update. I removed the replacement crankshaft and the top oil seal. I removed the counterweights from the crankshaft. I reinserted the replacement crankshaft, timing gear and camshaft. I did not attach the connecting rod. The timing gear was still not level with the camshaft. I repeated this set up with the original, damaged camshaft. I expected the gears to be level with each other, but no. They weren't. They're supposed to be, aren't they? It seems like every other time I've done this, the gears have been perfectly level. Maybe this isn't even my problem.

The flywheel end of the crankshaft isn't hitting anything on the outside of the engine block is it? on your work table etc?

This may sound stupid, but did you use a new sump gasket? Should be part number 697110 and have a thickness of .015”. If you are using the old gasket, it may be compressed too thin causing the problem.

The oil pump is driven off the end of the cam shaft .
When I reassemble these engines, I remove the oil pump then assemble it after the sump has been replaced & tightened
Check the cam is dropping onto the oil pump drive properly.