BROKEN ROD BOLTS ON MY WEST BEND 820! us motor power, chrysler

[alexcagle]

ANYONE KNOW WHAT CAUSED MY 820 US MOTOR POWER 2 CYCLE TO SNAP THE ROD BOLTS A COUPLE HOURS AFTER A TOTAL REBUILD? I TORQUED THE BOLTS AS SPEC'D. I PUT A NEW BLOCK, PISTON, ROD BEARINGS, & SEALS. I DID REUSE THE HEAD BOLTS, ROD BOLTS, ROD, WRIST PIN & BEARING, HEAD GASKET/SHIMS. THE NEW PISTON SEEMED TO HAVE THE SAME DIMENSIONS AND DID NOT SEEM TO HAVE ANY PROBLEMS RUNNING, ASIDE FROM LARGE CC "YANK YOUR ARM OFF TRYING TO START IT" COMPRESSION. THE ROD BOLTS WERE LOC-TITE'ED AND DID NOT BACK THEMSELVES OUT. THEY BROKE RIGH IN HALF. AFTER DETERMINING THAT IT WAS TO MUCH COMPRESSION TO START, I NOTICED THE HEAD HAD A BOSS FOR A DECOMPRESSION VALVE, SO I TAPPED, THREADED, AND INSTALLED ONE. I MADE DOUBLE SURE THERE WAS NO INTERFERENCE WITH THE PISTON AND THE DECCO VALVE. EITHER PUSHED IN OR OUT. THE HEAD GASKETS WERE MARKED WITH .010 AND THE OTHER WITH .020 . COULD I HAVE NEEDED MORE SHIMS AND GOT THE COMPRESSION TO HIGH? IT TAKES A MAN TO START THIS SAW. TWO HELPED, AS THERE IS NO THROTTLE LOCK ON THIS SAW. (NEVER WAS) THE ENGINE IS ON A RACINE RAILROAD PRODUCTS RAIL CUTOFF SAW WITH A 16" BLADE. FROM WHAT I UNDERSTAND ABOUT THIS MOTOR WHEN READING ABOUT IT ON THE INTERNET, IT WAS DESIGNED IN THE 50'S BY CHRYSLER/ WEST BEND AS AN OUTBOARD ENGINE, BUT FOR SOME REASON THE 30,000 OF THEM TOOLED UP DIDN'T GET SOLD. LEAVING A MANY 820 PARTS AS SURPLUS. US MOTOR POWER NOW HAS THEM, AND STILL SELLS PARTS FOR THESE ENGINES, AS WELL AS COMPLETE ENGINES. THEY STILL SELL THESE TO RACINE RR PRODUCTS TO PUT ON THIER SAWS. THEY LOOK LIKE A 4 STROKE AT FIRST GLANCE. THIS SAW WEIGHS ABOUT 45 LBS!
ANY HELP OR ADVICE WOULD BE APPRECIATED, MAYBE I AM MISSING A FUNDAMENTAL STEP IN MY REBUILD PROCESS? THANKS alexcagle

 

[ckelp]

maybe the bolts where over-torqued and over starched to the point they lost there holding capacity..

also, typing in caps is considered YELLING

 

[1steve]

My thought is this......rod bolts when properly torqued stretch. After the rod bolts are stretched and reused its possible when retorqued the stretched rod bolts are stretched to there yield point or to there limit the same as or equal to over torqueing. Results in broke bolts. Hope this helps

 

[1steve]

maybe the bolts where over-torqued and over starched to the point they lost there holding capacity..

also, typing in caps is considered YELLING

I'm a slow typer :hmm3grin2orange:

 

[ScottWojo]

What was the squish band like? And was there Too much compression? Too much compression and weak rod bolts?

 

[ckelp]

i forgot to add high stress bolts i almost never reuse,
if i pull a head off a genset i put new bolts in aswell i call it insurance...
i have two head bolts both the same size but one is over 1/2" longer then the other and has an hourglass shape on the collar...

 

[Busmech]

I ran a Monkey Wards hot saw with an 820 WB for several years with used rod bolts and no head gasket. The head was lapped onto the cylinder, it took me and my 6'3 240lb son to start it, never broke a rod bolt. I'm wondering if there was to much wear on the crank journal or maybe one to few needle bearings. It is also possible that the rod cap was on the wrong way, I believe they can only go one way like a Mac.

 

[alexcagle]

I ran a Monkey Wards hot saw with an 820 WB for several years with used rod bolts and no head gasket. The head was lapped onto the cylinder, it took me and my 6'3 240lb son to start it, never broke a rod bolt. I'm wondering if there was to much wear on the crank journal or maybe one to few needle bearings. It is also possible that the rod cap was on the wrong way, I believe they can only go one way like a Mac.

Monkey Wards.....I haven't heard that in a while......like since the 70's....
Sorry for yelling (ckelp). I'm 47, and it is easier to read for me in caps. I thought anyone who knew about an old engine might have old eyes as well......Sorry. I had to go there!...oh yeah; that's what what glasses are for.....
Those rod bolts are tiny, like maybe 5or 6 mm. I bet they should have been replaced with new ones on the rebuild. That makes sense to me; about the stretch staying stretched on the "stretch to yield". I had made sure I got all the rod bearings in there and I indexed the rod and cap prior to disassembly, so it wasn't that.
On the head gasket subject; you ran it without a head gasket? Or were the shims' sole purpose just a spacer?- and by "lapped" , do you mean you "honed it" flat to get a seal? Do you have to run special fuel for the increase in compression to avoid detonation?
I guess I'll get some more new parts for the saw again. But this time I even need the reed valve plate. The rod knocked the crap out of it. Plus the cylinder and piston got gouged badly. What a waste. Thanks for the input guys.
alexcagle

 

[cpr]

Not sure on the reasons, though I tent to agree on the not reusing bolts thing. I'D BE YELLING TOO IF I JUST THRASHED AN 820!!!