The shortest distance between two points...

[Kurt Bogerman]

Good evening, all.  I hope you are well. (These days, especially, it's more than just a polite remark!)


I recently acquired a MC10 "clone" engine that has not been run before in it's current configuration.  For various reasons, I've opted to disassemble it and make a couple changes before firing it up.  One thing I noticed is that the bore of the connecting rod's big end is not centered.  It is noticeably biased to one side.  I thought it might be interesting to hear some opinions about whether or not this is "within the manufacturer's specifications", or if it is a "defect", and if it has any detrimental or supplemental characteristics.  Maybe it's just an aesthetic issue, and I'm reading too much into it.  For what it's worth, my thought was to install it so the thicker side bears down against the crank through the power stroke.  Also, I'm not sure if this will have any geometric effects in the same vein as an offset wrist pin.  Any thoughts?

Here's some pictures:


  big end.jpg (Size: 392.47 KB / Downloads: 83)


  IMG_20200307_130329.jpg (Size: 3.58 MB / Downloads: 74)


  IMG_20200307_130420.jpg (Size: 3.74 MB / Downloads: 72)

[Terry Bentley]

Thats not a Mc10 rod, but looks just like every other Mc9 and newer rod I have seen. Some more and some less off centered. Unlike an offset pin, the center line of rod remains the same regardless which way it is installed.

[Alvin A Klusman Jr (Torque)]

NOTE THAT THE PISTON HAS BEEN NOTCHED ON THE "3RD PORT SIDE". This changes the piston port timing from that of an un-notched piston. Also you need to check the piston skirt legnth to see if it is a stock piston or a stroker piston. Stroker pistons are 0.080 longer skirt. Either one works on stock 1.50 stroke engines, but only a stroker piston doesn't freeport the exhaust ports on a 1.625 stroke Mc-10. If it is a stroker piston, the notch could be to retain the stock piston port timing. If it is a stock piston, the notch has changed the piston port timing from the stock timing. Best Regards "TORQUE"

[Kurt Bogerman]

Terry, 

You are definitely correct that the rod is MC9 or newer.  47903, if I'm not mistaken.  This is not a pedigreed, factory built MC10, it is a clone, with parts from a variety of sources, hahaha.  It's been a learning experience.  

I understand your point that the centerline of the rod is constant.  I have assumed that there might be a tolerance range for the position of the rod's bore.  If a factory team engine builder was hand picking parts, what might he think of that one?  Good?  Bad?  Indifferent?  Go fish?

Torque,  

Good eye!  I hadn't even thought to inquire about a detail like that.  I saw that notch in the 3rd port area of the piston skirt, but I assumed it was for clearance in the area of the side cover's main bearing.  I've never thought much about it before, but is third port timing of much influence?  If it hasn't been 9-ported?

Also, the piston is marked for MC6.  Any concerns or comments on that?


  IMG_20200227_182726.jpg (Size: 1.93 MB / Downloads: 37)

[Alvin A Klusman Jr (Torque)]

Terry, 

You are definitely correct that the rod is MC9 or newer.  47903, if I'm not mistaken.  This is not a pedigreed, factory built MC10, it is a clone, with parts from a variety of sources, hahaha.  It's been a learning experience.  

I understand your point that the centerline of the rod is constant.  I have assumed that there might be a tolerance range for the position of the rod's bore.  If a factory team engine builder was hand picking parts, what might he think of that one?  Good?  Bad?  Indifferent?  Go fish?

Torque,  

Good eye!  I hadn't even thought to inquire about a detail like that.  I saw that notch in the 3rd port area of the piston skirt, but I assumed it was for clearance in the area of the side cover's main bearing.  I've never thought much about it before, but is third port timing of much influence?  If it hasn't been 9-ported?  

Also, the piston is marked for MC6.  Any concerns or comments on that?

Kurt,

The piston markings indicate it is a stock bore (2.125) Mc-6 piston for a 1/8 (0.125) stroked crankshaft.   ( Bore 2.125 / Stroke 1.625 / 5.76 cid )
SO this IS a stroker piston.  Does your Mc-10 clone indeed have a stroker crankshaft (1.625 stroke)??  The piston is scolloped (probably a Moss ) so
that means the intake ports are effectivly raised from the stock location, without cutting on them. I'm sure that the exhaust ports have been squared,
(and maybe) raised. IF THE PISTON POPS OUT OF THE CYLINDER 0.0625 at top dead center it is a stroked Mc-10--IF NOT it is a stock stroke Mc-10.
If it is a stroked Mc-10, it will also have a head gasket AT LEAST 0.080 thou. thick or maybe thicker ( like 0.100 thou.or 0.125 thou. ).

The Mc-9 rod is a better rod-does not use thrust washers in the piston-has a smaller bottom end then even the Mc-10 stroker rod
( more crankcase clearance ). Also stronger!

Do you know how to use a degree wheel to measure the port timing of the engine?   You need to know when the exhaust opens--when the intakes open--
AND when the piston ports open (since the engine is not boost ported and is using the piston port intake).  Piston port timing CAN and WILL make a difference in how the engine runs when using the stock reeds and piston port type intake manifold!!


If you PM me your telephone number and best time to call, I'll call you and help you all I can!!  And give you my telephone number as well.

Best Regards,  "TORQUE"

PS--I'll tell you how to set-up the ignition on your Mc-10.  Set-up correctly it will run like a "Swiss Watch".  Done wrong and it will cause problems and blow condensers!!

[Kurt Bogerman]

Torque,

I will contact you soon to arrange a conversation. I'd be happy to "meet" you and learn whatever I can about this case study in parts assemblage. (I've already been picking some other brains about it: You know who you are, and I do thank you!)

I'll be in touch.

Kurt

[steveohara]

Kurt,

The appearance of your rod is very common and I have several examples that are much more offset. Often the appearance is somewhat deceiving and when checked with measuring tools I find the relationship between the big end bore and the rod bolt bores are very close. Have you measured the rod with the cap off to see if the bore is closer to one rod bolt than the other?
Steve O'Hara

[ted johnson]

Hey, Steve, Kurt and Al. If memory serves, Pop and I measured several Mc7, 8 and 9 rods that looked like Kurt's, back in the early days. All of them had the big end bore centered between bolt holes, but the aggregate of the three holes was off center with reference to the forging.
Hey, Al, I hope you're feeling well. Ted

[Kurt Bogerman]

Steve, I have not yet measured the bolt spacing, but I will. My original impression was that the big end bore appeared to be off center, such that a line drawn between bore centers would not be centered between the flanges of the I-beam from top to bottom, creating an asymmetrical load.

Ted, since you were scrutinizing rods, do you recall if there was any trend or consistency with regard to which way the rod was oriented during assembly, whether in production or in the workshop?  Now that we're discussing it, do you have any thoughts on the matter, even if they're idealistic observations?  I mean, could there be a best practice here?

During the manufacturing process, what could be the reason for the aggregate of holes being so sporadically positioned on the forging? Is there a datum point that is more subtle and variable than centering the holes on the centerline of the forging? Or is it all an optical illusion?

I assume that the process was not more precise because it wasn't important enough to demand more precision, but it sure seems like there's a lot more leeway given to this operation, compare to others.  Is machining the connecting rod the matter of least concern in a 13000 rpm reciprocating assembly? 

I've enjoyed the conversation.  Thanks for checking in!

[ted johnson]

It's been so many years since 1963/64 that I only remember doing the checking, but not the specifics. Remember, these were industrial engines, not true racing engines. They had ordinary workers building the engines, not Italian craftsmen. Most engines never saw 10,000 RPM, let alone 13K. The 7, 8 and 9 were not boost port engines, and weren't nearly as quick as a Mc90 or 91. They were saw motors sold as kart motors. I believe McCulloch deserves great credit for doing as well as they did, turning industrial engines into racing engines for a crowd of folks who, for the most part, were not tech trained racers, but grocers, doctors and bus drivers. The engines had amazing durability! Ted