Topic: 18HP Opposed Twin Performance Upgrade Path

[Jim Knutson]

Well today I added 4 degrees of timing and I also plumbed in a newer style plastic Briggs fuel pump and it seemed to run a little better except after running for about 5 minutes it shut down and then didn't want to crank over until it was completely cooled. The starter was getting super hot and not able to crank it over like it was locking up for some reason. I don't know what the heck is going on.

you are seizing a rod.

[BIG AL 202]

you are seizing a rod.

YUP COULD BE DOING THAT TO, CAN YOU TURN THE ENGINE OVER BY HAND, OR IS THE STARTER NOT TURNING IT? NEED MORE INFO, YES THEY ARE REAL GOOD AT SEIZING RODS, REALLY GOOD AT IT! YOU REALLY NEED TO KEEP THE CLEARANCES LOOSE ON AN OPPY!

[Scott P.]

Starter and battery are brand new. The cable is whatever size the mower came with, I didn't change it. It did this one time before I advanced the timing.

BETTER CHECK THE CONNECTIONS ON THE BATTERY AND ARE YOU USING THE RIGHT SIZE CABLE? IS THE STARTER NEWER OR OLD? DID IT DO THIS BEFORE YOU ADVANCED THE TIMING? SORRY FOR ALL THE QUESTIONS BUT WE DON'T WANT TO BLINDLY JUST GUESS.

[BIG AL 202]

LIKE JIM SAID YOU BETTER MAKE SURE THE RODS ARE NOT SEIZING UP, TRY TURNING IT BY HAND IF IT DOESN'T TURN TAKE THE COVER OFF AND CHECK RODS. YOU MY WANT TO DO THAT ANYWAY JUST TO MAKE SURE. USE PLASTIC GAGE AND CHECK CLEARANCES, ADD A THOUSAND TO SPECS [OR EVEN 1 - 1.5 MORE THAN THAT]. LET US KNOW!

[Scott P.]

Really even with all stock parts that ran fine before this can happen?

How do you guys open up the clearance? Hone out the big end of the rod?

The motor can be spun by hand but its hard to move, I will try spinning it cold and see if its easier when cold.

LIKE JIM SAID YOU BETTER MAKE SURE THE RODS ARE NOT SEIZING UP, TRY TURNING IT BY HAND IF IT DOESN'T TURN TAKE THE COVER OFF AND CHECK RODS. YOU MY WANT TO DO THAT ANYWAY JUST TO MAKE SURE. USE PLASTIC GAGE AND CHECK CLEARANCES, ADD A THOUSAND TO SPECS [OR EVEN 1 - 1.5 MORE THAN THAT]. LET US KNOW!

[Jim Knutson]

Here is what all I did with the motor:
-All of Don's oiling mods
-Clean up and smoothing of intake and exhaust ports
-ARC aluminum flywheel
-PCV ports in the block
-Fuel pump pulse port to the intake manifold
-Governor delete
-Dual 1.5" exhaust

no longer all stock parts.

Really even with all stock parts that ran fine before this can happen?

How do you guys open up the clearance? Hone out the big end of the rod?

yes, and yes.

[Scott P.]

Ok I will check this out when I get home.

Its odd because you would think the aluminum rod would expand as it got hot and would open up the clearance?

This motor hasn't seen over 3000 rpm yet also.

no longer all stock parts.
yes, and yes.

[BIG AL 202]

ALUMINUM EXPAND IN ALL DIRECTIONS, THE LAWS OF PHYSICS.  DON'T RUN IT TAKE OFF THE COVER AND CHECK FOR GALLING. I WISH I HAD A DOLLAR FOR EVERY TIME I SAW A NEW PART THAT WASN'T CORRECT OR THAT FAILED! DON'T EVER TAKE ANYTHING FOR GRANTED ESPECIALLY WILL ENGINE PARTS!

[Scott P.]

Well you guys were right. The lower rod was starting to seize up. Unfortunately I don't have time to mess with this motor anymore and I am going a different route. Stay tuned for a Opposed part out!

[avhac]

I did the following;
1. used a 42" engine
2. installed a cam out of a 46" engine
3. used a aluminum intake, ported
4. bored the carb spacer
5. ported/polished the journal to the valves
6. had the 4 screw carb jetted
7. had the heads milled flat
8. billet rods
9. billet flywheel advanced 3 degrees
10. sunoco 100 octane fuel

next will be bored/sleeved and de-stroked

as it sits it has @ 55hp and can hit 6500 rpms, not bad for an old black top flat head...

it will blow your mind!

[westcoast racer]

4. bored the carb spacer
5. ported/polished the journal to the valves

What do you mean by Ported/Polish the journal to the valves?
And what did you do to the carb spacer exactly?

[PJG56]

I did the following;
1. used a 42" engine
2. installed a cam out of a 46" engine
3. used a aluminum intake, ported
4. bored the carb spacer
5. ported/polished the journal to the valves
6. had the 4 screw carb jetted
7. had the heads milled flat
8. billet rods
9. billet flywheel advanced 3 degrees
10. sunoco 100 octane fuel

next will be bored/sleeved and de-stroked

as it sits it has @ 55hp and can hit 6500 rpms, not bad for an old black top flat head...

it will blow your mind!

How did you determine you have 55hp??

[redline]

2. installed a cam out of a 46" engine

That's how....stock cam for the emissions friendly win!

[cycloneracer]

I did the following;
1. used a 42" engine
2. installed a cam out of a 46" engine
3. used a aluminum intake, ported
4. bored the carb spacer
5. ported/polished the journal to the valves
6. had the 4 screw carb jetted
7. had the heads milled flat
8. billet rods
9. billet flywheel advanced 3 degrees
10. sunoco 100 octane fuel

next will be bored/sleeved and de-stroked

as it sits it has @ 55hp and can hit 6500 rpms, not bad for an old black top flat head...

it will blow your mind!

I'd guess closer to 20hp. 

Although I do know a guy with a dyno and I will pay for the dyno time if it is 55 or higher. 

[PJG56]

I,was thinking the same thing,maybe he's giving it a 35 shot of nitrous.