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Briggs and Stratton 33R877 Timing Issue

#1

G

gman2023

May I please get advice on how to repair my Briggs & Stratton (model 33R877) ridemower engine? I'm at my wits end trying to fix this engine.

I'll explain what happened to the engine, and how I tried to repair it. The piston rod broke, killing the engine. The piston rod and the crankshaft needed replacing as a consequence (scouring marks were present where the piston rod attached to it). After cleaning the engine case out, I put the engine back together, but it won't start correctly. Here is what I observe:

1) The electric motor spins the crankshaft.
2) The spark plug does spark.
3) A puff of air blows out of the carburetor, right after sucking air in.
4) The chamber does hold compression, but is released out of the carburetor (I believe this must be the compression release mechanism on the camshaft).
5) The engine does fire when I spray starter fluid into the intake valve, but the exhaust immediately blows out of the intake.
6) The flywheel key is intact, with no obvious damage.
7) The intake rocker arm is spaced to 0.005", and the exhaust rocker arm is 0.006" (the steel pusher rod is on the exhaust valve, aluminum rod on the intake). Spaced the rocket arms with the piston 0.25" down from TDC, both valves closed.
8) The carburetor, SAE 30 oil, gaskets, piston rod, crankshaft, air filter, oil filter, and gasoline are all new.
9) Camshaft compression release seemed OK, no obvious damage to the camshaft either.
10) Flywheel was removed at one point, but put back into place.

I thought I aligned the camshaft and crankshaft (both have dots that one aligns). The only thing I can think of that could be the issue is maybe somehow the camshaft is not aligned with the crankshaft, but how? I thought I aligned these. Is there something that I'm missing? The problem is that ignition takes place with the intake valve open, which to me seems like a timing issue. Either the camshaft/crankshaft are misaligned, or its an electrical timing issue (at least, that's my theory).

Below is a youtube video of that exact same engine model that I'm using. The video is what I followed to put everything back together:


Any advice would be awesome and greatly appreciated, I'm not sure what to do anymore.


#2

I

ILENGINE

May want to recheck the flywheel key. If not properly torqued can shear easily. Either that or you miss timed the gears. Crankshaft gear keyed to crankshaft and camshaft gear slippage would break the compression release


#3

StarTech

StarTech

Also can be a severely exhaust cam lobe wear but that would visible by checking the rocker arms movement, they should be the same amount. Also cam timing can checked somewhat TDC Exhaust stroke the valves should be swapping right at TDC.

Otherwise the OP needs to go back in and do a timing check.


#4

T

Tbone0106

Usually, when these Briggs one-lungers break, the connecting rod pops out through the side of the engine casing. (That failure, incidentally, is almost always due to low oil. Proper oil level is VITAL in these engines.)

The block is probably hopelessly tweaked. I can't imagine why you didn't just trash the whole business. Big-bore Briggs motors are a dime a dozen.


#5

B

bertsmobile1

Take the plug out and poke a skewer down the hole
Rotate the engine by hand and note where the piston is as the inlet & exhaust valves open & close
I use a timing tape wrapped around the flywheel


#6

G

gman2023

ILENGINE said:
May want to recheck the flywheel key. If not properly torqued can shear easily. Either that or you miss timed the gears. Crankshaft gear keyed to crankshaft and camshaft gear slippage would break the compression release
Click to expand...
Will do. Later today I'll doublecheck the flywheel key and see if it is damaged. Based on all the comments I'm getting, I'm going to open the engine again and check the gear timing, along with checking the crankshaft gear and if its keyed to the crankshaft properly.


#7

B

bertsmobile1

I like to check externally before opening up an engine which at the best will mean new gaskets & if you are very careful oil seals as well
Wrap a run of masking tape around the flywheel and rotate the engine till at TDC compression stroke ( both valves closed )
Mark a lin on the tape using the side of the magneto
With different coloured pens mark the opening & closing of the valves .
Every time you open up an engine you do damage to the threads so the least often the better
The tape will confirm that the valves are out of time or not .


#8

G

gman2023

ILENGINE said:
May want to recheck the flywheel key. If not properly torqued can shear easily. Either that or you miss timed the gears. Crankshaft gear keyed to crankshaft and camshaft gear slippage would break the compression release
Click to expand...
I went ahead today and inspected the flywheel key, it was intact, no sign of shear or damage. My next step then is to make sure that A) the crankshaft is timed to the camshaft, and B) the crankshaft gear is keyed to the crankshaft.

I did notice that the ignition coil is almost touching the flywheel, I wonder if the spacing gap between the flywheel and coil can cause ignition timing error? I'll look up what the correct spacing is supposed to be.


#9

B

bertsmobile1

Closer advances the spark, further away retards the spark
Gap should be ≈ 0,010"
You could try moving the magneto back further to see if the problem goes away
Full amount of movement is less than 1 tooth .


#10

R

rgrottk

Check your timing as stated above and make sure the valves are closing properly and that the valve guides have not moved.


#11

doug9694

doug9694

gman2023 said:
May I please get advice on how to repair my Briggs & Stratton (model 33R877) ridemower engine? I'm at my wits end trying to fix this engine.

I'll explain what happened to the engine, and how I tried to repair it. The piston rod broke, killing the engine. The piston rod and the crankshaft needed replacing as a consequence (scouring marks were present where the piston rod attached to it). After cleaning the engine case out, I put the engine back together, but it won't start correctly. Here is what I observe:

1) The electric motor spins the crankshaft.
2) The spark plug does spark.
3) A puff of air blows out of the carburetor, right after sucking air in.
4) The chamber does hold compression, but is released out of the carburetor (I believe this must be the compression release mechanism on the camshaft).
5) The engine does fire when I spray starter fluid into the intake valve, but the exhaust immediately blows out of the intake.
6) The flywheel key is intact, with no obvious damage.
7) The intake rocker arm is spaced to 0.005", and the exhaust rocker arm is 0.006" (the steel pusher rod is on the exhaust valve, aluminum rod on the intake). Spaced the rocket arms with the piston 0.25" down from TDC, both valves closed.
8) The carburetor, SAE 30 oil, gaskets, piston rod, crankshaft, air filter, oil filter, and gasoline are all new.
9) Camshaft compression release seemed OK, no obvious damage to the camshaft either.
10) Flywheel was removed at one point, but put back into place.

I thought I aligned the camshaft and crankshaft (both have dots that one aligns). The only thing I can think of that could be the issue is maybe somehow the camshaft is not aligned with the crankshaft, but how? I thought I aligned these. Is there something that I'm missing? The problem is that ignition takes place with the intake valve open, which to me seems like a timing issue. Either the camshaft/crankshaft are misaligned, or its an electrical timing issue (at least, that's my theory).

Below is a youtube video of that exact same engine model that I'm using. The video is what I followed to put everything back together:


Any advice would be awesome and greatly appreciated, I'm not sure what to do anymore.
Click to expand...
Perhaps the camshaft is bent from when the rod broke. I put it in the base hole and turn it to see if it wobbles. And make sure the base hole is not cracked.


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