Vintage Karting Forum

All,

Quietly, I was a very early adopter of KPrecision's new high strength connecting rod bolts for West Bend engines. I had been watching the conversation on this forum and elsewhere regarding the current shortfall in supplies of quality connecting rod bolts. As soon as information appeared regarding these newly available bolts, I immediately ordered two pairs; one for a project and one to keep as spare parts. The specific project was a McCulloch 91B for which I was in the process of acquiring the last few parts to complete. I intended to shorten the bolts, chamfer the con-rod cap, and install.

The bolts were in my possession for several weeks before I actually acquired the connecting rod for the 91B project. In that meantime, I heard that there were, possibly, issues with the thread fit of some of the bolts that had reached the market. I heard that these issues were resolved by contacting Jeff Kniseley at KPrecision and exchanging the bolts for correctly fitting replacements.

Upon receipt of the connecting rod, which I had purchased from an experienced and reputable vintage karter, I hurried to test the fit the bolts. I was disappointed to discover that they would not thread into the rod using fingertips alone. I put it down and left a voicemail for Jeff K the next morning, explaining what I was trying to do and what I was experiencing, and that I had heard of someone else's issues with the bolt fit.

Jeff called me back very promptly, and we discussed the details of my situation, including the fact that I intended to use the bolts in a McCulloch application. I do not recall if I described the fact that I would need to shorten the bolts. Jeff advised that the fit of the bolts was tailored to West Bend connecting rods that he had gauged, but that he had no data regarding the thread class of McCulloch's rods. He explained that he knew what the issue was with some of his early bolts and that he was pretty certain that he had isolated all of the affected pieces. He advised that if I were to oil the bolts and attempt to install them with a nut-driver, that they should install with a small amount of resistance, and that he was not surprised that they could not be threaded in with fingertips alone. He gave me the option to try them again, or to send them to him to be rechecked. I opted to try again.

I oiled the bolts and used a ¼” nut-driver and 5/32” socket to drive the bolts. Like he described, using the nut-driver I was able to thread them in with some resistance that, while greater than originally expected, was not alarming, especially given Jeff's description of the incredibly close thread fit that he had spec’d for these bolts. Satisfied, so far, I proceeded to shorten the bolts by stacking up several 10-32 nuts on the threads of each bolt and progressively grinding them to length, cooling them frequently with water. I removed the nuts and dressed the lead thread with a file. The bolts were able to be fully threaded in and out of the rod several times, with similar resistance to that experienced before the modification. I used a Dremel tool and a fine conical stone to grind a chamfer in the rod cap to accommodate the underhead radius of the bolt.

Feeling increasingly confident, I proceeded with the assembly of the engine; pressing the piston pin, fitting the rings, and installing the piston/rod assembly into the block. Needles in place in the crank journal, it was time to screw in the rod bolts. This time, with a ¼” ratchet at hand, I started both bolts, and began to drive them in, alternating from one to the other in stages. Suddenly, it happened: “TINK!”. What a nauseating sound and feeling! One of the bolts had snapped off, flush in the connecting rod. Neither of the bolts were seated yet, so it wasn't the chamfer at fault, and I hadn't even had a chance to apply the torque wrench.

So… All of this makes any analysis of the situation complicated, at best. Was it the fit of the bolts? Is the fit satisfactory for West Bend but incompatible with McCulloch? Was it the fact that I modified the bolts? Was it the fact that I was driving the bolt with a ratchet, rather than a nut-driver? I'm not a professional engine builder, though this 41 year-old has been turning wrenches on his own cars, toys, and equipment since he was a pre-teen. Maybe that "increasing confidence" had overpowered these 10-32 screws? I repeat… Lots of complicating circumstances here.

In the immediate days after breaking that bolt, I sought advice and/or commiseration from several folks with whom I've become acquainted in the last several months since preparing for and attending my first VKA meet in May. All of them STRONGLY encouraged me to get in touch with Jeff at KPrecision about the situation. Frankly, I was inclined to take this on the chin, procure a replacement rod, and move on, but, after dwelling on it over this past weekend, I figured that I'd send Jeff an email explaining what happened.

I spent my entire lunch hour, this past Monday, crafting an email to Jeff. I first recounted our original conversation about the fit of the bolts. Then I explained what led up to the broken bolt. I assured him that I and others in the vintage karting community appreciate his efforts and really want his investment in our hobby to be successful. I acknowledged that my scenario was complex, but also stated that what I did was not novel and has had a successful track record with previously available hardware. I mentioned, too, that a solution for the impending lack of McCulloch hardware was something of some concern within the hobby. I reiterated in several ways that I had contacted him only in the hope that from my scenario some valuable information or experience could be gleaned.

Jeff K replied to me within ten minutes of my hitting "send".

His demeanor was polite and constructive. He asked some clarifying questions about what had happened. He asked for me to send him all four bolts, both modified and unused, as well as the rod itself. He offered to attempt to extract the broken stud from my connecting rod, and expressed his interest in gauging the threads in the rod to gather some McCulloch specs for possible use moving forward. I hope that my rod's specs are typical and that those measurements will be useable. As an aside, I wonder if it might be a good idea for others to loan known-good rods to Jeff to broaden his data sample size, but that's just my own idea. Jeff says that he is sitting on a new batch of bolt blanks that haven't been headed or heat treated. He is apparently in the process of rechecking his specifications, in case he needs to roll those threads to a revised specification

Jeff received my rod and bolts yesterday and is in the process of gauging the threads and examining the returned bolts. He says that he will work on the rod early next week. At the very least, he intends to return to me bolts that he will modify in his shop to be used in my McCulloch application. He is definitely interested in the McCulloch market, and advises that anyone interested in using his bolts in a Mac should order directly through the KPrecision website and specify that intention. He says that he would prefer to prepare the bolts in-house for these situations, at this point. It sounds likely that, if there is demand, that he would mass-produce bolts for the McCulloch market in addition to West Bend.

The fate of my connecting rod is still uncertain, but it is clear to me that Jeff is proactively addressing my situation. The circumstances of my situation are unique, including my modification of the bolts and my use of them in an engine for which the bolts were not designed, and these details make it difficult for me to be too critical of the bolts at this point. Regardless, Jeff is working with me and has repeatedly expressed his desire to work with all of his customers to provide the products and customer service that we need. I would suggest that anyone watching this situation should reserve judgement of the bolts until the dust settles and the facts regarding these bolts become more clear.

I would be very interested to read comments from other karters who have purchased the bolts. Did they fit correctly? Have you installed them and used them in a running engine? Does my favorable impression of Jeff's commitment to our needs ring true to you?

Please, chime in.

Best regards,

Kurt

Kurt, Kudos on doing your due-diligence. As an aside, I have very successfully shortened the Engine Masters' (Dave B.) socket head West Bend screws and used them in a modified Mc101. There was absolutely no issue aside from carefully shortening them by running a nut down onto the screw and gently cutting the tip off with a Dremel tool and cutoff wheel, cooling the screw during the cutting op by squirting it with brake cleaner. I then squared, smoothed and re-chamfered the end of the screw with a Proxxon mini-belt sander, holding the screw in my fingers as a heat gauge. If it begins to get hot to the fingers, squirt it with brake cleaner. I chamfered the rod cap with a 90 degree stone in the drill press. The screws went into the Mac rod threads with my fingers. I had no trouble torquing the screws to my usual 115 In-Lbs. If this West Bend screw worked just fine in the Mac rod, any quality West Bend screw ought to work. I don't know what thread class Jeff is rolling onto the K Precision screws, but almost all 180-190KSI black oxide screws such as the standard West Bend and Mac rod screws are class 3 threads. Hang in there. A solution has to be found. I'd say that K Precision has enough time invested to make it imperative for Jeff to follow through. Having had a detailed discussion with Dave B. about alloys, under head fillets and thread rolling processes, I have a newfound respect for the engineering effort required to make such a small screw do the huge job we require of it. I admit that I found one set of Dave B.'s original 12 point head run of the multiphase alloy screws from one of our favorite kart shop owners, so my Libberton is covered, but Engines must be rebuilt and the n1ke 610 has already had the screws reused the one time. I'd hesitate to use them again. I may well save the ones I got this morning for the modified n1ke engine, and put lesser screws in the near-stock engine. I was looking yesterday at a set of 1/4" ARP screws that are going into Ron Cubel's World Formula Briggs. The shank has a sort of hourglass shape, presumably to distribute the stretching stresses. Very smooth shank. Nifty screw. Too bad they don't make 10-32 screws to that spec. Ted

interesting thread i'll be watching it.
 as an aside does jeff have an account on this forum?
if not maybe somebody can suggest he join so he can find and converse with potential customers directly through the forum.
d

Kurt - thanks for sharing that information with us.
Paul

My suggestion for what it's worth is DO NOT attempt to cool the bolt when shortening . Let it air cool only. Water is the worst thing you can do. If you were to use anything other than just letting it air cool, oil would be the choice. I would prefer to not even use that. I also don't know what was used to shorten them. Heat is your enemy (and that cooling process kills the metal) . I use a number 36 belt on a 6 x 48 grinder (usually well worn). I don't get them very hot.

Steve, that's why I used the Dremel cutoff wheel very gingerly. It doesn't get the screw very hot if you are careful. I bought a miniature variable speed belt sander to dress the tip after cutting. The sander can run very slowly, so as not to heat things up. I figure if I can't hold the part in my fingers, it's too hot. I took a 1-1/4" x 1/4" steel bar and drilled and tapped several sizes of hole in it. I run a jam nut on the screw, run it into a tapped hole so that the amount to be cut off sticks through and gently tighten the jam nut. I saw the tip off with a fine tooth saw blade and use the mini sander to smooth the tip while it's still threaded into the bar. I then loosen the jam nut and remove the screw, and chamfer it on the little sander. The screw never gets hot, and I can do everything but chamfer the tip while it's clamped in the vise. Seems to work. I use black oxide set screws for head studs, and secure West bend heads with Allen nuts and ARP hard flat washers. I've cut many 1/4-20 studs to length this way. TJ

Steve,

Thanks for your advice. I can definitely appreciate the principles that you are addressing.

I held the screws with a 5/32" socket on a 6" long, 1/4-drive extension, and kissed it to a 6" bench grinder. I supported the screw and retained it in the socket between the thumb and forefinger of my left hand, and rotated the extension between the thumb and forefinger of my right. My left hand was gloved, more for protection from the wheel rather than for protection from heat, with the side effect being that I would not have felt the bolt temperature. I would touch the screw to the grinder wheel for only one or two quick rotations at a time, then dip in water. I don't recall any dip that resulted in a sizzle. But, then again, we are discussing a bolt that broke, aren't we? It is certainly possible that the structural integrity of the bolt could have been affected, though I made an effort to avoid that.

-Kurt

Christensen Rod bolts $5.00 pair.

If we had only known..........

When is that ad from, Tom? I can't tell if that's more or less than $40.00/pr in 2018 dollars.