Hey guys. Wanted to ask and see if you knew why this happens. I'm trying to put in piston/rod combination #4. Problem is... the clearance between the side wall on the crank and the other rod (#3) isn't enuff for the #4 rod to slide in !! If force it in it will go in, but it takes A LOT of force and still doesnt fully engage. I thought I had #3 in backwards, but the notch does face the front of the block and so is #4. These piston/rods were taken out of their orginal locations and numbered... so these two rods coexisted toghether on that same journal for a long time. Why wouldnt it go in now ?! Any ideas ?

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92 Z28 L98 350
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Ported and polished heads, ported stock TPI base, ported plenum, Comp Cams XR270HR-10 cam (lift .495/.502 duration 218/224 lobe separation 110), Edelbrock TES headers, LT4 valve springs, Crane AFPR, Flowmaster catback with LT1 style tips, MSD coil & wires...

"Take that auto, drop it in first, hold the brakes, stomp the gas and grin from ear to ear! :-)

 

I'd say a rod was put on backwards on the piston.

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Stephen's racing page

87 IROC-Z Pro ET Bracket Race Car and knocking on the SuperPro ET class
383 stroker (carbed) with double hump cast iron heads and pump gas
LS6 Big Block buildup now in progress

Best results before the engine blew up
Best ET on a time slip: 11.857
Best corrected ET: 11.163
Best MPH on a time slip: 117.87
Best corrected MPH: 126.10
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!

Member of the Calgary Drag Racing Association

 

Is there any "burr" on the caps??

If they came out they should go back.

Are you sure the bearing is centered and not peeking out of one side??

So you just took apart a short block, re-bearinged it, and are re-installing the rods ...right??

Unless there is an obstruction, it should go.

Whatever you do, don't force them in.

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ASE Mechanic/Machinist/Smog Tech

1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R

GO #3

 

That's exactly what I did. All the rods are going back to their exact same locations. I dont think the bearing is misaligned since the tang probably won't let it, but I'll take a look. Maybe by mistake I have the other rod with the cap on backwards ?! lol
I'm gonna go look when I get back home Thanx guys

p.s. if any more ideas pop up, pleeeease let me know

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92 Z28 L98 350
---------------
Ported and polished heads, ported stock TPI base, ported plenum, Comp Cams XR270HR-10 cam (lift .495/.502 duration 218/224 lobe separation 110), Edelbrock TES headers, LT4 valve springs, Crane AFPR, Flowmaster catback with LT1 style tips, MSD coil & wires...

"Take that auto, drop it in first, hold the brakes, stomp the gas and grin from ear to ear! :-)

 

Stephen is exactly right, one or both of the pistons are on the rod backwards. Happens all the time.

The bearing tangs (and the factory-stamped numbers) should go on the outward side of the rod, that is, away from the cam. In fact in early small blocks there was a little oil passage notched into the opposite side of the rod to squirt some oil up into the underside of the cylinder for pin & ring lube.

One of your checks before assembling a motor should be: lay all the parts out on a table, in the physical orientation they need to be in when installed. That will allow you to spot things like that.

Check all your rods carefully and take them back to the shop if incorrectly assembled.

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"So many Mustangs, so little time..."

 

While I agree... I don't see why GM would have messed this up ?! The pistons were never taken off the rods. Everything's original GM with X rods, which I heard are better than plain stuff. I mean I took these babies apart, so they did coexist on the same journal in the SAME exact position for years! LOL I'm begging to think there's something wrong with the way I installed the other rod. Anyway... thanx for the tips RB

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92 Z28 L98 350
---------------
Ported and polished heads, ported stock TPI base, ported plenum, Comp Cams XR270HR-10 cam (lift .495/.502 duration 218/224 lobe separation 110), Edelbrock TES headers, LT4 valve springs, Crane AFPR, Flowmaster catback with LT1 style tips, MSD coil & wires...

"Take that auto, drop it in first, hold the brakes, stomp the gas and grin from ear to ear! :-)

 

Any more ideas guys ? :/

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92 Z28 L98 350
---------------
Ported and polished heads, ported stock TPI base, ported plenum, Comp Cams XR270HR-10 cam (lift .495/.502 duration 218/224 lobe separation 110), Edelbrock TES headers, LT4 valve springs, Crane AFPR, Flowmaster catback with LT1 style tips, MSD coil & wires...

"Take that auto, drop it in first, hold the brakes, stomp the gas and grin from ear to ear! :-)

 

Blade,

#1. Got calipers? Check the remaining space on the crank throw and compare it to the rod end width.

#2. Assemble the two holes in reverse order;

#3. Snug (don't torque) the rod cap bolts on the #3 to see if the rod "realigns" itself, making space for the #4.

#4. Did you check the rods or rebore them? Make sure the bores are parallel. Was the crank machined, rolled, or undercut?

#5. As a last resort, assemble the rods on the throw with the pistons out of the cylinders.

#6. Are you certain of the numbering sequence? Looking at the case from the oil pan side makes everything upside-down/bass-ackwards, and can get confusing. (See diagram)


I'm thinking one of them is assembled backwards as well.

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

 

Just a WAG, but you said #3 is in and you are trying to put in #4. I am assuming the #3 cap is already on the rod. Are you sure its not on backwards? The caps will fit either way but if I remember right its a little offset. Make sure its on there right as well.

 

Okay guys I fixed the problem (sort of). Cylinders 3&4, and 7&8 were installed in the wrong bores. I took em all out and put em in backwards. It looks like I put em in backwards to start with and didn't notice it. Now the little "scrapers" on the side of the rods are pointed towards the outside of the joint where the two rods come toghether on the journal and there's at least 0.018 clearance between the rods now. The engine still spins kinda hard even with a wrench on the damper bolt. Maybe it's because the rings are new or maybe because the crank and rods and everything else dont have a whole lot of oil on em yet. Anyway, I'm going to go ahead and put the oil pan on it then continue to assmemble it. The way I see it, this is only a temporary engine until my engine gets fixed by Spartan engines anyway (which might take months). Thanx again for all the help. It was my screw up after all! lol

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92 Z28 L98 350
---------------
Ported and polished heads, ported stock TPI base, ported plenum, Comp Cams XR270HR-10 cam (lift .495/.502 duration 218/224 lobe separation 110), Edelbrock TES headers, LT4 valve springs, Crane AFPR, Flowmaster catback with LT1 style tips, MSD coil & wires...

"Take that auto, drop it in first, hold the brakes, stomp the gas and grin from ear to ear! :-)

 

How about this one. Are you sure you didn't mis-read cyl 8 as cyl 3? If you did & installed it with the by correct piston oreintation, the rod would be backwards.
Regards, FJK

 

Well that would be kinda impossible since I had the pistons ligned up one after another from 1 trough 8. I did one by one, but my guess is that instead of putting 3 into the #3 bore I put in #4 instead. LOL

I noticed that when I looked down at the wrist pin. On #1 and #2 with the caps on and tightened down the wrist pin/rod was almost centered in the piston. #3 and #4 were hitting side wall on both. That's when I knew something was terribly wrong. LOL So now they're all centered and clearances are met. Regards, Edmond