Connecting rod bolt

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REAR
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Re: Connecting rod bolt

Post by REAR » Thu Mar 15, 2018 6:04 pm

Dave,

Agreed, that crank does look very suspicious and in need of some attention

As for $40.00 rod bolts there are alternatives. Think about all the hours that Mc engines have been run over the years with out those expensive rod bolts, probably millions of hours. Did they run all those hours and countless races on those expensive bolts...NO so you can ask yourself, do you need to buy them now, who knows ?

Have been using Danaher brand 'Allen' bolts that come in a sealed and certified box and have never had a rod bolt failure. Are they bulletproof, not saying... nothing really is.

Suggest that you call a reputable fastener dealer-distributor and ask what they have available. Remember, stay away from anything you can get a home and garden chain stores.

R.E.A.R.

Rob Voska
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Re: Connecting rod bolt

Post by Rob Voska » Fri Mar 16, 2018 6:26 am

* Be careful of the brand you use. Lots of cheap foreign fasteners out there.
* Make sure all mating surfaces, seating surfaces and threads are clean.
* Small drop of loctite on threads.
* Torque properly.

Long time ago when this all started Bob bought a box of bolts. I put together a 91 engine out of old very sub prime parts and used those bolts. If it blew up I was not out much. I have over revved that thing & never had a problem with it.

Remember the job of rod bolts is to hold the rod cap in location. Under compression the cap has no load. The crank is pushing up on the rod. When the engine fires at TDC the piston is now pushing down on the crank throw and putting the rod in compression again. The cap just guides the needles.

One thing I always try to pay close attention to is clearances & needle tracking. If crank journal is small or rod is not round then you are going to have trouble.

Other than wear the other way to damage a rod is to seize an engine. It was turning thousands of RPM and comes to a brief stop. That puts everything I said above in reverse and can oblong a rod cap in a split second.

So think...... What came first the chicken or the egg. Did the piston seize and stop the piston and all the rotational forces and energy contained in the crank, flywheel, starter cup, clutch, just rip the rod cap off....... or did the rod bolt break that was under no real load until the piston stopped, break? How many times in it's life has that rod and crank assembly been seized is probably a better question to ask.

Think about this in a multi cylinder engine. If you have one dead cylinder you very well could have a bad cylinder getting dragged along. That is where you are trying to stretch a rod by both pushing and pulling it.

REAR
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Re: Connecting rod bolt

Post by REAR » Fri Mar 16, 2018 7:51 am

You don't want to be this guy.

Image

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Mark Loraine
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Re: Connecting rod bolt

Post by Mark Loraine » Sat Mar 17, 2018 7:52 am

I can save you the trouble of asking a snap on tool truck driver to match this bolt head, nothing even in the catalog. Also do not try to remove these with a conventional ¼” socket, it will not work.
I seem to recall it being a “Bristol” named pattern for the head. Also a part number search on google turned up nothing!

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Russ Smith
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Re: Connecting rod bolt

Post by Russ Smith » Sat Mar 17, 2018 12:21 pm

I bought the 1/4" drive socket for this from GEM a few years ago. Might be some still available .

ted johnson
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Re: Connecting rod bolt

Post by ted johnson » Sat Mar 17, 2018 1:02 pm

I've no idea it the Mac rod screws are true Bristol pattern, but go to
https://bristolwrench.com/
and check it out. Ted

REAR
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Re: Connecting rod bolt

Post by REAR » Sat Mar 17, 2018 5:34 pm

https://en.wikipedia.org/wiki/List_of_screw_drives

It may be a polydrive or ribe.

R.E.A.R.

Rob Voska
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Re: Connecting rod bolt

Post by Rob Voska » Sun Mar 18, 2018 6:23 am

Another thing to pay attention to it where the rod bolt seats on the rod cap. Some of the bolts with built in washers have a small radius. The washer part on the under head of the bolt needs to seat on the spot faced areas of the rod cap without any interference of the radius. if the radius hits first it is trying to split the rod cap from the bolt area. The hardened rod cap may crack and well........ you know what happens next.

Chris Marchand
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Re: Connecting rod bolt

Post by Chris Marchand » Sun Mar 18, 2018 1:08 pm

Bang, Boom, Rattle rattle ? Silence ........

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.

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