4l80e dowel hole smaller than the 6.0 block dowel

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johnnunez29

Master Mechanic
May 9, 2022
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Gm, been running into all sorts of dumb problems and this is the latest. i went to mate the trans to block and it wouldnt get flush, pulled out some sanding paper and sanded the dowel hole on trand and the dowel pins, then i used a digital caliper and found that the dowel pins (engine) are .6215 and the dowel pin holes (trans)are .6115 . I called a few places, trans builder, engine builder even jegs. apparently no ones ever seen this. i cannot get a smaller dowel or it wont fit the block so what i am planning on doing is reaming the hole with a 5/8 ream (closest to what the dowel should be (.6250) my question is this. If the dowel doesnt fit super snug, is that an issue? i dont think itll have a ton of play but it may not be too snug.
 

69hurstolds

Geezer
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Jan 2, 2006
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Dowel pins aren't typically tight fitting as a rule. Some are and some aren't. Theoretically, a 35 thousandths of an inch bore difference once you open up that hole isn't going to hurt you. That's a spark plug gap. I'm guessing you're using a transmission that originally wasn't for an LS block? Just asking, I don't mess with LS and transmission combos. The bolts are keeping it tight. The dowels are simply for ease of alignment for assembly. The bolts, when properly torqued, are going to keep your transmission tight to the block.
 
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johnnunez29

Master Mechanic
May 9, 2022
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Dowel pins aren't typically tight fitting as a rule. Some are and some aren't. Theoretically, a 35 thousandths of an inch bore difference once you open up that hole isn't going to hurt you. That's a spark plug gap. I'm guessing you're using a transmission that originally wasn't for an LS block? Just asking, I don't mess with LS and transmission combos. The bolts are keeping it tight. The dowels are simply for ease of alignment for assembly. The bolts, when properly torqued, are going to keep your transmission tight to the block.
Trans was supposed to have come off the same ,a 6.0 block. If I use a 11/16 bit then it’s too small. So 5/8 is the closest I can get. You basically said what I was hoping to hear.
 

johnnunez29

Master Mechanic
May 9, 2022
277
63
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Trans was supposed to have come off the same ,a 6.0 block. If I use a 11/16 bit then it’s too small. So 5/8 is the closest I can get. You basically said what I was hoping to hear.
Thank you
Drill with a 15.5mm drill (.6102") preferred or a 39/64" (.6094") drill.

sh*t 80.00 to possibly ALMOST make it in 😳. Think I’ll take my chances with the 20.00 5/8 reamer. If anything I’ll paint the studs to make them thicker lol
 

64nailhead

Goat Herder
Dec 1, 2014
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I wouldn't ream the trans - bad juju will happen if you're off by .005-.010".
 
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69hurstolds

Geezer
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Jan 2, 2006
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I wouldn't ream the trans - bad juju will happen if you're off by .005-.010".
Great point. Yeah, my brain wasn't even engaged with that. If your centerline is too messed up between the engine/trans, it could be problematic for the bearings in both engine and transmission. May want to hold off on just hogging out the holes.

All I can say is there's either the wrong dowels in the engine or something is amiss with the transmission holes. I've never heard of this issue before between engines/transmissions that supposedly are made for each other. Ever.
 

johnnunez29

Master Mechanic
May 9, 2022
277
63
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I wouldn't ream the trans - bad juju will happen if you're off by .005-.010".
Not much of an option. What else could I do? I sanded the dowels and the hole to get the paint out and Thai is what I got.
 

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johnnunez29

Master Mechanic
May 9, 2022
277
63
28
Great point. Yeah, my brain wasn't even engaged with that. If your centerline is too messed up between the engine/trans, it could be problematic for the bearings in both engine and transmission. May want to hold off on just hogging out the holes.

All I can say is there's either the wrong dowels in the engine or something is amiss with the transmission holes. I've never heard of this issue before between engines/transmissions that supposedly are made for each other. Ever.
sh*t that’s the same thing I heard from the engine builder AND the trans guy. Engine builder checked a bunch of ls he had and they were all different. I’m kinda stuck. Need to do something.
 
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