Connecting rod bolt

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steve welte
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Re: Connecting rod bolt

Post by steve welte » Tue Apr 03, 2018 9:15 pm

So I read the comment above stating that the engines ran all these years without a special 40 or 50.00 bolt. while that is true one also needs to know that all the factory McCulloch rod bolts were indeed special and not just a grade 8 or 9 bolt you can buy anywhere. We have contacted dozens of manufactures now that everyone is out of Factory bolts and everyone of them will tell you that a bolt of this size and of the PSI/K of the factory bolt does not exist. Other than our small engines there is no need for a bolt like we need so no one makes one. We approched a company for a special bolt to be made but the cost escalated to $22.00 a bolt on a 1200 bolt purchase. While many claim they have success with this bolt or that, i have lost 3 engines to the one many say to use. NO MORE. At $700 to $1000.00 an engine I'll let someone else use bolts from a box that cost 12.00 per 100. Is your engine worth a $.12 bolt? The special bolts from USMP are all gone at this time but an alternative may be in the near future. For our sake we better hope so. My only suggestion is if you have someone building your engine I hope you know what he is using. Good Luck.

REAR
Posts: 705
Joined: Sat Jun 16, 2007 10:19 am

Re: Connecting rod bolt

Post by REAR » Wed Apr 04, 2018 6:19 am

Steve,

Great info and insight that is very much appreciated in this discussion. Personally have never lost a motor to a rod or bolt failure, maybe just lucky but your experience says otherwise and that's why we need this discussion. Not trying to advocate or promote anything.

Food for thought, short of a known stock McCulloch engine personal experience has been that a good majority of the used engines I have disassembled have a 'allen' type bolt in the rod not the factory spline headed bolt. Many of these same motors have been modified before I received them and after just a bearing, seal, electric rebuild and clean up they spun more then a stock engine so the fact that they were intact and showing some signs of wear when I received them somewhat proves that they had been run and that the 'allen' type bolt was prevalent and widely used in the day.

Will relate a interesting story, As I just finished torqueing the rod cap on a brand new rod, needles, and crankshaft on a Mc92 the telephone rang, as I proceed to walk away from the motor to answer the phone I heard a 'plink' noise. I knew right away that the rod had broken and sure as sh.. it did. Needle count was correct, cap was acclimated and torqued correctly plus I also always rotate my engine between each torque increase to check for any abnormalities or bind and everything was smooth as new. Cause of the break, I have no idea but the rod bolts were not broken or cracked and I know I got real lucky which leads to the question is the rod bolt always the culprit in a catastrophic failure and are they being blamed for other unseen issues that lead to the rod bolt failure ?

Keep us updated on any progress you come up with because the whole idea of historical karting is the save and run the karts from the old days and anything that we can do to keep them running longer the better.

R.E.A.R.

ted johnson
Posts: 1365
Joined: Fri Jun 15, 2007 7:59 am

Re: Connecting rod bolt

Post by ted johnson » Wed Apr 04, 2018 9:59 am

All of us are hoping that Steve and company come up with a viable alternative. It's certainly true that some rod failures can be attributed to the rod or cap, and not the screws, but it's equally certain that some failures can be attributed to screw failure. I'm running open 610 West Bends. The blocks are getting scarce, and it isn't cheap getting Mr. Bonbright to modify them, though Lord knows it's worth his reasonable cost. I don't want to lose a valuable block due to the lack of a proper screw, even though it costs $50-$60 for two of them. With the USMP/Bonbright screws, the screws were reusable, at least. Let's all hope that an alternative in the 250/260 KSI tensile range can be quickly found. Oh, yeah! If the new proposed screw has a fillet between underside of head and shank, the hole in the rod cap needs to be chamfered. I found a 90° fine grinding burr that I use. A special word of thanks to Steve Welte for his efforts! Ted

steve welte
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Re: Connecting rod bolt

Post by steve welte » Wed Apr 04, 2018 12:46 pm

that the 'allen' type bolt was prevalent and widely used in the day.

This is correct as the standard series and saws used the allen head style bolt but those were still a special grade not available today. NO they were NOT just a 180K grade 8 or 9 screw. They were in the area of 210K with the external spline 101 being in the 220 k range. Also be aware there is a difference between shear and tinsile strength.

steve welte
Posts: 17
Joined: Fri Feb 04, 2011 7:22 pm
Vintage Karting items owned: mc 92
User Agreement: Yes

Re: Connecting rod bolt

Post by steve welte » Fri Apr 06, 2018 9:55 pm

Good news is pending. Probably next week we will know more.

steve welte
Posts: 17
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Re: Connecting rod bolt

Post by steve welte » Fri Apr 06, 2018 10:12 pm


ted johnson
Posts: 1365
Joined: Fri Jun 15, 2007 7:59 am

Re: Connecting rod bolt

Post by ted johnson » Sat Apr 07, 2018 9:14 am

Steve has kept after this and has pushed Jeff K. at USMP to get something done about the matter. I think a big vote of thanks MUST go out to Steve! Thanks! Ted

steve welte
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Joined: Fri Feb 04, 2011 7:22 pm
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Re: Connecting rod bolt

Post by steve welte » Sat Apr 07, 2018 4:09 pm

Further info on these bolts is that they are 280 KSI tinsile strength and 236 KSI yeild. The initial run is a very small quantity with the next runs being larger. Torque is to be 95 to 100 inch pounds. Be sure to only use a six side socket and NOT a 12 point. The first sets use a 5/32" socket and the second run will use 3/16 socket.

ted johnson
Posts: 1365
Joined: Fri Jun 15, 2007 7:59 am

Re: Connecting rod bolt

Post by ted johnson » Sat Apr 07, 2018 4:45 pm

Might be a good idea to take the rod cap to the tool store when you buy your 6 point socket. Some brands may not fit into the recess in the rod cap. I just checked my 3/16" 6 point 1/4" drive socket against a rod Steve sent me, and it clears fine. I can't find a 5/32" 6 point in the shop, but Craftsman, Proto and Snap On have 'em. TJ

REAR
Posts: 705
Joined: Sat Jun 16, 2007 10:19 am

Re: Connecting rod bolt

Post by REAR » Sat Apr 07, 2018 5:14 pm

Steve,

Is Kperformance a mfg. or a supplier ?

Have you had past experience with them ?

R.E.A.R.

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