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Rod is Tight on the Crank
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petrol punk
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PostPosted: Sun Apr 24, 2011 7:34 pm    Post subject: Rod is Tight on the Crank Reply with quote

I've started assembling the bottom end of my stock 36hp, and I've run into a problem of one of the rods binding up once I torque it down. I double checked the oil clearance and it comes out to .0015" and tried swapping rod bearings and switching it between rod journals and the problem persists. I'm trying to think of how to solve this problem. Anybody got any ideas on how to alleviate this problem? My only idea is to hone the rod big end to open it up but then I think my oil clearance would open. Maybe I just need a new rod?
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Bashr52
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PostPosted: Sun Apr 24, 2011 8:43 pm    Post subject: Reply with quote

Its just the one? Could the rod or crank be slightly our of round?
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petrol punk
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PostPosted: Sun Apr 24, 2011 10:51 pm    Post subject: Reply with quote

Yeah, just one. I tried swapping the rods around the different journals and the journals seems fine, the problem only follows the one rod. I tried bolting up one of my brother's rods and it felt alright.
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Snort
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PostPosted: Mon Apr 25, 2011 6:39 am    Post subject: Reply with quote

I had to re-size my rods on my 36hp after they came back from balancing. There's just not a lot of metal there on the rod cap and they can distort quite easily apparently.
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avus
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PostPosted: Mon Apr 25, 2011 5:06 pm    Post subject: Re: Rod is Tight on the Crank Reply with quote

petrol punk wrote:
I've started assembling the bottom end of my stock 36hp, and I've run into a problem of one of the rods binding up once I torque it down. I double checked the oil clearance and it comes out to .0015" and tried swapping rod bearings and switching it between rod journals and the problem persists. I'm trying to think of how to solve this problem. Anybody got any ideas on how to alleviate this problem? My only idea is to hone the rod big end to open it up but then I think my oil clearance would open. Maybe I just need a new rod?


I'll probably catch some crap for this, but it's worked for me: The rod bolts align the rod and cap on 36 and 40 hp VW's. There can be slop in the fit of the threads and between the bolt and the hole in the cap--sometimes enough to cause the bearing halves to misalign.

Try this: 1 snug the rod bolts evenly to where the rod just starts to bind on the crank. 2 With a small hammer, smack the connecting rod on the parting line, perpendicular to the rod bolt, toward the crank pin, from each side. 3. If this loosens up the bearing, torque the cap to spec and spin it around a few times to see if anything changes. If it's still sticky, admit it--you need to replace or resize the connecting rod. If it turns freely, it's a good idea to take it back apart and check for serious shiny spots on the bearing. If it's cool repeat steps.

Fire away!
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hazetguy
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PostPosted: Mon Apr 25, 2011 7:04 pm    Post subject: Reply with quote

i've done the above method with success. also, I forget who told me or where I read that a trick to do when assembling 25hp, 36hp, and early 40hp rods (non self aligining), is to fit feeler gauges between the rod and crank. It takes away the "wiggle" space of the rod and cap, so that the rod stays in alignment while torquing the rod bolts. It seems to work very well.

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avus
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PostPosted: Tue Apr 26, 2011 7:52 am    Post subject: rod cap alignment Reply with quote

hazetguy wrote:
i've done the above method with success. also, I forget who told me or where I read that a trick to do when assembling 25hp, 36hp, and early 40hp rods (non self aligining), is to fit feeler gauges between the rod and crank. It takes away the "wiggle" space of the rod and cap, so that the rod stays in alignment while torquing the rod bolts. It seems to work very well.


I like. This would minimize axial misalignment that could affect side clearance binding. Good trick.
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Bart Dunn
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PostPosted: Tue Apr 26, 2011 3:22 pm    Post subject: Reply with quote

Make sure there are no burrs under the rod bearings, too. They can hide close to the edges where the machining is done, or there can also be a burr between the rod and the cap--same thing, sort of hiding along the edge.
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Matthew Tolbert
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PostPosted: Thu Aug 06, 2015 7:55 am    Post subject: Reply with quote

Bringing back this old thread because I had the same issue with one of my rebuilt rods I got from rimco. When I first torqued it down it would bind in a couple of places so I took it apart and there are some shiny spots on the bearings only on the NON tang end of each. I found this thread and was able to get it moving freely by tapping the rod like mentioned and I also found some very small burrs at the parting line that I sanded down. My question is are the bearings on that rod ruined and need replacing? I'd hate to have to buy another set and wait for them but will if necessary.
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Mr. Motorhead
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PostPosted: Thu Aug 06, 2015 3:09 pm    Post subject: Reply with quote

They should be okay. Does the rod move okay now?
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Matthew Tolbert
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PostPosted: Thu Aug 06, 2015 3:28 pm    Post subject: Reply with quote

Yes the rod moves perfectly now. That's good to here about the bearings.
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akomjathy
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PostPosted: Thu Aug 20, 2015 2:15 pm    Post subject: Reply with quote

I have a problem with one of my stock rods in my freshly rebuilt 40 HP engine. It seems the rod hits the crankshaft when turning around the engine. It knocks and has an ugly noise. It makes in one point on the 3rd cylinder, when it goes to the top direction. The piston doesn't touch the head. Here is a video:

http://youtu.be/kJkbwYni4Uc

What do you think? The cranshaft is a standard size one, with very low mile. I put NOS vw bearings and NOS Kolbenschmidt rod bearings. The case is perfect.
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Matthew Tolbert
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PostPosted: Thu Aug 20, 2015 5:19 pm    Post subject: Reply with quote

Did it turn free when it was just a short block? Is the cam indexed correctly? Take the rockers off and try to turn it. May be hitting a valve.
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akomjathy
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PostPosted: Sat Aug 22, 2015 1:36 pm    Post subject: Reply with quote

I took off the rockers already. The knocking is on, when there are no lifters in the engine case, too. For sure the rod hits the crankshaft. I stressed the back side of the rod to the crankshaft side with a big screwdriver and there is no knock!! Here is a pic:

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Matthew Tolbert wrote:
Did it turn free when it was just a short block? Is the cam indexed correctly? Take the rockers off and try to turn it. May be hitting a valve.
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