Tech Support Forum banner
1 - 5 of 5 Posts

· Registered
Joined
·
3 Posts
Discussion Starter · #1 ·
Hello all
I’m currently rebuilding my Briggs and Stratton riding mower engine 31C707-0026 G1 100916ZDI and now I cannot get it to start. When I’m cranking the engine over it’s back firing very loudly and producing a lot of white smoke as well as spitting a lot of oil from the valve cover. During the rebuild I made sure that the two dots on the cam shaft and timing gear were lined up correctly and there are no broken crankshaft keys or flywheel keys. I purchased a leak down tester last night and ran 100 PSI at TDC (compression stroke) The results were about a 15-18% leak. Hissing could be heard coming from the breather tube which was connected to the intake tube as well as hissing could be heard coming from the dipstick tube when I removed the dipstick. I took measurements of the bore from the top, middle and bottom with a telescoping gauge and measured with a dial caliper with a result of 3.563in which matches appropriately with the service manual. So at this point I’m thinking that this has to be an issue with the piston rings and causing blow by. I did purchase a new piston during this rebuild (p/n 594539) and I am fairly certain that I followed the instructions correctly with making sure the paint lines were to the right of the gap and making sure to use the correct ring for the center ring. I also made sure that no ring gaps were lined up with each other upon placing the piston back in. Did I miss something? Are the gaps suppose to be at a certain position on the piston (center ring at 2 o’clock position 8 o’clock position, etc) ? What am I missing?
 

· Registered
Joined
·
5,890 Posts
Assuming that the rings are the correct size, installed in the proper order and manner, and that there is not a lot of scoring on the cylinder walls, you may have a stuck ring. Did you oil the grooves first? Also, double-check the timing too and make sure the valves move freely and seat completely.
 

· Registered
Joined
·
3 Posts
Discussion Starter · #5 ·
If the ring gaps are all lined up then air can leak past the pistons, they should be 180 degrees apart (assuming that there are two). Stuck valves can cause a compression leak too. Also, make sure you didn't break a ring while installing it.

To the best of my knowledge all the gaps on the piston were not lined up when I put the ring compressor on. Rings don’t appear to be broken and I do not have any stuck valves. I took the rings off and put them in the cylinder to measure the gaps and they are all within normal limits according to the service manual. I am in deep doo doo now because the paint marks on the top of the piston rings are no longer there so now I don’t even know how to determine the orientation of the rings. :unsure:
 
1 - 5 of 5 Posts
Top