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My twenty year old 10 HP Briggs (205412-0120-E1) threw a rod and I’m in the process of rebuilding the motor with a new rod (694691) and rings. Problem is that the rod tightens onto the crank journal when the con rod bolts are tightened to 50% of spec (spec = 100 in*lb). Below are pics of the rod and journal when I rotate the rod dry with bolts tightened half of spec:



Prior to rebuild I sanded the crank journal using 1000 grit sandpaper and WD40. I don’t believe the failed crank left any aluminum on the journal and the crank surface looked perfect after sanding. I measured the crank diameter at 1.2500 inch using a calibrated Mitutoya caliper having a resolution of 0.0005". Using ID snap gages I measured the ID of the con rod at 1.2495 inch when tightened to spec. Obviously I have an interference condition.

I added two 0.006" paper shims under the ends on the con rod cap and got the rod to spin but that’s not a permanent fix.

Is my con rod out of specification or am I doing something wrong?

What radial clearance should I expect to see? For example, a 0.002" rod gap should yield a rod ID of 1.254".

Interesting spec for a larger INTEK B&S engine shows the crank diameter to be 0.001" under nominal.

I might be wrong, but do you know your code date?
i ran into this problem once, but it was with the wrist pin end... turns out i had the wrong rod for my code date.. so it may be the right diagram you ordered from and same model #, but the wrong code date specific part...
maybe someone else who has access to that info will be along shortly.

Code: 000817YD

None of the few online sites I checked made a distinction by date code.

Briggs shows a crank rod journal dimension of 1.2485

I have resized a couple rods over the years, easy to go a bit too far and get it tight. I use a piece of aluminum foil to get the clearance back to spec. Like to have about .001 clear or so on small journals. Rule of thumb is .001 per inch of journal diameter. Cheap foil is thin, good stuff is thicker.

ILENGINE said:

Briggs shows a crank rod journal dimension of 1.2485

Click to expand...

Is it practical to try to take off 0.0015 off the diameter of the crank journal using 400 fine emory paper then finish with 1000 grit?

Go-Rebels said:

Is it practical to try to take off 0.0015 off the diameter of the crank journal using 400 fine emory paper then finish with 1000 grit?

Click to expand...

Not really practical because it would be hard to keep it round. The picture with the crank kind of looks like it could still have a small amount of aluminum smear on it thou.

ILENGINE said:

Not really practical because it would be hard to keep it round. The picture with the crank kind of looks like it could still have a small amount of aluminum smear on it thou.

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Yes, the pic of the crank journal does have some aluminum on it as i wanted to show the contact marks on the rod and cap as also shown in the other pic. Suffice it to say that it was perfectly clean prior to tightening the cap on the crankshaft and giving it one one rotation when tight.

I've tried to get some 0.002" thick brass shim stock but it is unavailable at any of the auto parts store I've checked including O'Reilly's, Advance Auto and NAPA. Maybe I need to go to a craft store next.

As a trial I will try next to shim the rod cap using some heavy duty aluminum foil as tom3 suggested.

Oh gosh my mind is slipping. Taryl has some sort of chemical he uses that removes aluminum transfer... aaarhhh gosh i cant remember the name of it...
you know what im talking about IL?

Edit: Hydroclhoric acid. Thats it.

Scrubcadet10 said:

Oh gosh my mind is slipping. Taryl has some sort of chemical he uses that removes aluminum transfer... aaarhhh gosh i cant remember the name of it...
you know what im talking about IL?

Edit: Hydroclhoric acid. Thats it.

Click to expand...

A strong mixture of Lye and water (or "Mr. Muscle" oven cleaner) works well too and is easier to obtain than hydrocloric acid. I've used it already with no effect; my crank journal is clean steel.

Go-Rebels said:

A strong mixture of Lye and water (or "Mr. Muscle" oven cleaner) works well too and is easier to obtain than hydrocloric acid. I've used it already with no effect; my crank journal is clean steel.

Click to expand...

Hydrochloric acid is sold as Muriatic Acid in any farm store, or Walmart, or Pool supply store.

Plastic baking tray / dish with just enough acid in it to cover the journal by 1/2" left in the sunlight for a couple of hours to warm up then slip the crank in slowly
10 minutes to 1/2 hour will be fine wash very well with hot SOAPY water then rinse in hot water, boiling is best because the crank will dry quickly and it MUST BE OILED the second it is dry or it will rust.
Neutralize the HCl with chlorine.
Muriatic acid is a commercial grade of Hydrochloric acid before it is distilled in glass.
IT is generally pale green to yellow because of the residual iron left over from the production.
Getting rid of the iron is very expensive which is why Muriatic is dirt cheap & Hydrochloric is a lot more expensive

The problem is that my crank measures a little bigger than standard after being cleaned and that the original rod ID was obviously larger than the standard replacement rod ID that I can purchase today. I suspect that Briggs may have produced some out-of-spec cranks and had a batch of larger-than-normal rod bores produced to fit the cranks. It's certainly cheaper to ream out a connecting rod a little bigger than reset a crank in a centerless grinder and turn it down a little. Maybe Briggs always had a small supply of bigger rods at hand to build rather than rework.

I'm not entirely keen on shimming the rod cap mating surfaces because the surfaces are milled with a small step to center the cap over the rod. When I add a shim across both stepped surfaces I not only raise the cap relative to the rod (good) but I also create an interferance at the step and therefore slightly bend the cap putting the inside of the cap into tension (bad). Given that these connecting rods are marginal by design in the first place, I hate to add further stress to the cap but that might be the only way to get the clearance that I need.

I'm going to chemically clean the crank once again and polish using 1000 grit sandpaper then take it to a local machine shop and have them measure the journal OD again. Measuring with a 6" caliper is not the optimum method; I need a 1-2" micrometer which I do not have.

Journal OD measures 1.2485" using a calibrated 1-2" vernier micrometer. I can read that with my 6" digital calipers with some wriggling.

Bottom line: measure using a micrometer.

It does not take much alloy on a journal to make it tight so give it the acid treatment as others have suggested.
A single high spot will cause it to bind and dragging a bit of wet & dry over the journal does not work unless it is backed onto something flat & solid
It will just stretch over a 0.005 high spot.
I preferred the caustic soda bath over the acid bath , but both will strip any alloy off the journal.
After that a polish with a brass brush usually brings them up perfect.

Hello,

Also, your aluminum rod expands a lot more than your cast iron crank will when hot, so at operating temperature you may have enough clearance.

Regards

Jeff

bertsmobile1 said:

It does not take much alloy on a journal to make it tight so give it the acid treatment as others have suggested.
A single high spot will cause it to bind and dragging a bit of wet & dry over the journal does not work unless it is backed onto something flat & solid
It will just stretch over a 0.005 high spot.
I preferred the caustic soda bath over the acid bath , but both will strip any alloy off the journal.
After that a polish with a brass brush usually brings them up perfect.

Click to expand...

I will chemically clean the journal again this weekend and try to refit.

I don't think I can get past a 0.005" high spot. Did you mean 0.0005"?

jp1961 said:

Hello,

Also, your aluminum rod expands a lot more than your cast iron crank will when hot, so at operating temperature you may have enough clearance.

Regards

Jeff

Click to expand...

I need enough clearance to get the rod to spin on the crank when cold, and tightened to spec, else I obviously can't pull start the motor.

I'm not keen on shimming the rod cap. If after chemically cleaning he crank I'm still tight then I'll just send the crank back and order another.

I guess its to small for your local machinist to grind it to the correct size?

Down here it is cheaper to buy a new crank than to have an old one resized.
Crank grinding is a very specailzed job and yes finding a grinder with a small enough wheel to fit the journal can be a problem.

Hello,

Heres just a thought without going the machine shop rout or buying a new crank.

Apply a small amount of valve lapping compound to the rod journal, and rod cap, assemble the rod and cap with the rod bolts slightly loose and rotate by hand a bit to remove several tenths i.e. .0001". Maybe an electric hand drill could be used to slowly rotate the crank?

Obviously you'd have to throughly clean everything prior to final assembly.

OK after thinking about this (and drinking a second cup of coffee,,,lol), valve lapping compound may be too coarse, but there are "cleaner" auto waxes that contain a mild abrasive that might be a better choice. There also is a product called Liquid Ebony", that is a super fine rubbing compound that removes swirl marks left by coarser rubbing compounds.

Regards

Jeff

If the crank is round I'd work on the rod. Machine shops have reamed out wrist pin bores for auto engines since forever, simple operation. Take the crank and rod down to the local NAPA shop (or whatever is handy) and let them work it out.

Fellas, remember I bought a new replacement rod that doesn't fit. I've already measured my crank journal and found it to be within specification so I'm not grinding the crank. Now I need to find a rod that fits without modification... no shimming, no lapping, no reaming. It's got to be out there.

When you tighten the rod bolts are you using a small tension wrench ?
I have a 6" wrench that reads 30 ftlbs at full scale.
I bought it particularly for doing swing back blades which are done up from 10 ftlbs to 20 ftlbs.
Also remember the torques for con rods are generally given in INCH pounds not Foot pounds.

bertsmobile1 said:

When you tighten the rod bolts are you using a small tension wrench ?
I have a 6" wrench that reads 30 ftlbs at full scale.
I bought it particularly for doing swing back blades which are done up from 10 ftlbs to 20 ftlbs.
Also remember the torques for con rods are generally given in INCH pounds not Foot pounds.

Click to expand...

http://www4.briggsandstratton.com/miscpdfs/RNT/Engine Specifications Chart_ms3992.pdf

bertsmobile1 said:

When you tighten the rod bolts are you using a small tension wrench ?
I have a 6" wrench that reads 30 ftlbs at full scale.
I bought it particularly for doing swing back blades which are done up from 10 ftlbs to 20 ftlbs.
Also remember the torques for con rods are generally given in INCH pounds not Foot pounds.

Click to expand...

Yes, I’m using a small Snap-On torque wrench that reads in in-lb.

I know it's a long shot, but you might call or email Briggs with your model number give them the crankpin journal spec and give them the rod part number you ordered and see if they can figure anything out.
I'd also give them your Code number.

Slightly off subject, but have been seeing lot of torque specs in in/lb that are outside the setting limits of the wrench. Like 325 for sump bolts, or 370 for head bolts, or in some cases 750 in/lb for some hydro inner parts. Yes you can convert to ft/lb but if your ft/lb wrench is off accuracy by much that can mean a big error in in/lb.

I just ordered and received another rod from Amazon. It fit perfectly and no binding after torqued to 100 in-lb.

Good rod casting: "MAG 5A", cap "8C"
Bad rod casting: "MAG 3A", cap "11C"

Go-Rebels said:

I just ordered and received another rod from Amazon. It fit perfectly and no binding after torqued to 100 in-lb.

Good rod casting: "MAG 5A", cap "8C"
Bad rod casting: "MAG 3A", cap "11C"

Click to expand...

:thumbsup::banana::cool2::cool2::cool2::banana::drink:
Way to go!! Glad you got it figured out..
was the rod a different part number (im assuming so) than the first? or was just a good rod and you got a bad one..
as taryl would say
"Wooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo!!"
https://youtu.be/q_DrnItIKwA?t=5010 :laughing:

Scrubcadet10 said:

was the rod a different part number (im assuming so) than the first? or was just a good rod and you got a bad one..

Click to expand...

Exact same part number ordered but different casting numbers on the rod and cap after opening the box. I don't believe the casting numbers are a date code as there aren't enough digits to define a day/month/year for an entire year.

Another interesting point is that the journal surface of both the rod and cap appear shiny 'as cast.' I don't see any machining marks of any kind.

I spoke to a guy at work who is very knowledgeable about aluminum die casting. He tells me that the cap and rod are milled on the mating surfaces only. The cylindrical oil bearing surfaces are ‘as-cast’.

Follow up thread: "Rebuilt 10hp Briggs Won’t Start."

ILENGINE said:

Hydrochloric acid is sold as Muriatic Acid in any farm store, or Walmart, or Pool supply store.

Click to expand...

Yeah, I believe Muriatic is a cut version of Hydro--, used by brick masons to clean mortar off bricks.

Walt Conner

Go-Rebels said:

I need enough clearance to get the rod to spin on the crank when cold, and tightened to spec, else I obviously can't pull start the motor.

I'm not keen on shimming the rod cap. If after chemically cleaning he crank I'm still tight then I'll just send the crank back and order another.

Click to expand...

I don't think you can shim that rod. I also think you have not cleaned all deposited metal from crank. Other wise. install and torque the rod cap bolts and have machine shop ream/bore polish rod to necessary ID.

Walt Conner

Tinkerer200 said:

Yeah, I believe Muriatic is a cut version of Hydro--, used by brick masons to clean mortar off bricks.

Walt Conner

Click to expand...

Muriatic Acid is the old name and generally used to describe the raw, unrefined solution.
Most of the muriatic acid is obtained as a by product from other processes so gets sold as Muriatic.
When actually made by reacting Hydrogen & Chlorine gasses then dissolving in distilled water is is called HCl and generally around 4 times the price.
Because it is usually a byproduct Muriatic is often a pale pink or green.

bertsmobile1 said:

Muriatic Acid is the old name and generally used to describe the raw, unrefined solution.
Most of the muriatic acid is obtained as a by product from other processes so gets sold as Muriatic.
When actually made by reacting Hydrogen & Chlorine gasses then dissolving in distilled water is is called HCl and generally around 4 times the price.
Because it is usually a byproduct Muriatic is often a pale pink or green.

Click to expand...

Maybe in Australia, clear color here and still called Muriatic on label.

Walt Conner