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rebuilt engine wont crank

#1

A

Alex1121

Hi I have a 25 horse Briggs and it blew a connecting rod so i took it apart and installed 2 new rod and rings. i honed the cylinders, lapped the valves and cleaned the heads. when I put the crank shaft back in it spins freely but once I hook up either of the connecting rods it becomes so hard to crank over that i need to put a pipe wrench on the crank to get it to move and if i hook up the other rod it becomes even harder to crank over. I already checked and made sure that all the parts I have are correct . Any idea what would be causing this problem?


#2

B

bertsmobile1

Wrong rods or build up of aluminium on the journal.
Nuts done up too tight, specks are generally in INCH pounds not Foot pounds.
With the crank out do the rods up., lube them first.
If they are correct you should be able to spin then around with your little finger and keep them spinning by flicking the crank.

Rods also come is a couple of oversizes so you might have a 1st oversized rod.


#3

A

Alex1121

I checked all that before installing the rods and pistons but the still wont move. Moving the piston in the cylinder is hard even without the crank connected but then when you do install the crank is becomes almost impossible to move them. i checked the piston and cylinder for damage and didn't find anything and also checked the new rings and they aren't over sized either. the info that comes with the rods when you buy them says to torque to 100 inch pounds so that's what i did


#4

S

shiftsuper175607

Alex1121 said:
I checked all that before installing the rods and pistons but the still wont move. Moving the piston in the cylinder is hard even without the crank connected but then when you do install the crank is becomes almost impossible to move them. i checked the piston and cylinder for damage and didn't find anything and also checked the new rings and they aren't over sized either. the info that comes with the rods when you buy them says to torque to 100 inch pounds so that's what i did
Click to expand...

Try one cylinder at a time and compare them to each other and for movement.


#5

John R

John R

Is it possible that when the rod broke it tweaked the crank?


#6

S

shiftsuper175607

Alex1121 said:
Hi I have a 25 horse Briggs and it blew a connecting rod so i took it apart and installed 2 new rod and rings. i honed the cylinders, lapped the valves and cleaned the heads. when I put the crank shaft back in it spins freely but once I hook up either of the connecting rods it becomes so hard to crank over that i need to put a pipe wrench on the crank to get it to move and if i hook up the other rod it becomes even harder to crank over. I already checked and made sure that all the parts I have are correct . Any idea what would be causing this problem?
Click to expand...

Did you "mic" the inside diameter of the cylinders and the outside diameter of the pistons/rings
There should be manufacture numbers for those readings and clearances.
The rings ends should have clearance/gap on the piston when compressed.

From where I sit(a long way off) and what you are saying...the piston is too tight in the cylinder to move....that is the problem to solve.


#7

Ronno6

Ronno6

Clean the carbon build up out of the ring grooves in the pistons...........
Carbon may prevent the rings from seating in to he pistons sufficiently and cause binding.

Just a thought.........


#8

L

Luffydog

Possibly got the rods in the wrong way


#9

dfbroxy

dfbroxy

Have you found a solution yet? If so share it with us. If not did you prelube before assembly?


#10

A

Alex1121

Thanks for all you help. It turns out that the crank was tweaked just enough that it was pinching on the connecting rods without being overly obvious


#11

S

shiftsuper175607

Alex1121 said:
Thanks for all you help. It turns out that the crank was tweaked just enough that it was pinching on the connecting rods without being overly obvious
Click to expand...

New engine?

New mower?

Lawn service?


#12

A

Alex1121

just replaced the crank after taking it apart again and now its running just fine. Its off of a toro sandpro and its from a golf course


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