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Piston Ring End Gap & Conrod Positioning

Alcyone

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Got 2 things going on with a rebuild; VY V6 3.8L Ecotec...

(1) 2nd ring end gaps are measuring at 0.48mm-0.50mm whereas the Haynes manual is showing specs wanting to be in between 0.762mm-1.016mm.
I rang the machining shop where some work was done and where I got the Hastings rings from. Chap there said that the measurements I'm getting are well within spec and that he himself would still fit them without any filing. Any thoughts? I am also getting 0.48mm-0.50mm with the top ring and the Haynes manual is wanting 0.305mm-0.559mm for those ones. All seems okay with them. Why are the 2nd rings so tight? Should I leave them as is or should I file them back? I only have the Haynes manual to refer to yet the chap at the machining shop said that the measurements I'm getting are fine. Oil control rails are also within spec.

(2) When putting the pistons back onto the rods, I am placing the notch on the piston (see pics) towards the front of the engine. I had everything in order before taking stuff to the machining shop and they even engraved the pistons etc. But putting them back together, I'm not sure which way to face the rods. (EDIT: The rods were removed from the pistons and I'm not sure when putting them back together which way is up or down). They have an assortment of numbers on the front and back but all those markings seem pretty random. Is there any way to definitely read something on them to know? Chap at the machining shop said to place the bearing tang insert 'left of centre'. Can someone explain that any better please? Does that mean that the tang goes in the upright position when putting the rod caps back on? When I say upright, I mean upright when I'm looking at things with the engine upside down and I'm able to screw the bolts in from that position. I didn't explain that very well. The way I've taken the photo is what I mean. Tang up the top which I guess means left of centre of the crank?

Cheers if anyone can provide some information :)

Pic 1 - Showing tab on piston which means its positioning to front of engine.
IMAG4801 (Medium).jpg



Pic 2 - Showing tab on piston facing the front and the bearing tangs on the upper side of the big end.
IMAG4804 (Medium).jpg
 

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What does the ring manufacturer recommend for the ring gaps. I believe the 2nd ring gap should be a bit wider than the top ring.
 

EYY

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.003" ring gap for every 1" of bore size for standard cast pistons.

In high heat/high performance applications you generally need a little more clearance (thing forced induction, nitrous, forged pistons etc.)
 

Alcyone

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What does the ring manufacturer recommend for the ring gaps. I believe the 2nd ring gap should be a bit wider than the top ring.
I checked the Hastings website and found this;
https://www.hastingspistonrings.com/tech-tips-faqs/checking-compression-ring-gaps
It says pretty much what EYY said in his post. I then multiplied 3.8" x 0.0035 and got 0.0133" which is = to 0.33782cm
Looking at the pic below (thanks Haynes for this), it shows a weird gap for the 2nd ring. But is it right? The first ring gap is within spec but the 2nd one is way out! When I hold the top and 2nd ring on top of each other, there is about a 2mm wider gap on the 2nd ring but when they're in the bore, they become identical with their end gaps. I'm kinda stumped here. I only pushed the rings down about 3-4cm to measure them but it wouldn't really matter as the bores are only meant to be OOR and out of taper by no more than 0.01mm (even though mine slightly exceed that).
IMAG4809 (Medium).jpg
 

EYY

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Disregard those specs in the manual when you use aftermarket rings. Always use the specs supplied by the piston/ring manufacturer (different thermal properties between different ring materials can even play a role).

Btw use a piston to push the rings down into the cylinder so that the ring is sitting square (measure towards the bottom of the cylinder where the rings don't contact to get an accurate measurement).
 

Alcyone

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Disregard those specs in the manual when you use aftermarket rings. Always use the specs supplied by the piston/ring manufacturer (different thermal properties between different ring materials can even play a role).

Btw use a piston to push the rings down into the cylinder so that the ring is sitting square (measure towards the bottom of the cylinder where the rings don't contact to get an accurate measurement).
Cool thanks. Yep new OE Hastings rings. Makes sense now. I used a piston to push it down about 4cm from the head side. I'll also get a measurement from a couple cm from the crank side.

Sounds like having the same end gaps on top and 2nd rings is okay then. Thank you!

Any ideas which way I should face the rods? I read that V8's have reversed tangs for the odd number cylinders but the V6's have them all facing the same way forward. Is it right to have all the tangs facing up? Or is it that I have all the tangs left of centre? Or is that the same thing?

(EDIT: "Holden red/blue and black V8 conrods are installed as follows. Conrods 1, 3, 5 and 7 have the machined tab on the bottom of the conrod facing the *front* of the engine. In other words they line up with the notch in the front of the piston. Conrods 2, 4, 6 and 8 have the machined tab on the bottom of the conrod facing the *rear* of the engine. In other words they face *away* from the notch the front of the piston. They *don't* all face the same way like they do in a six. A noticeable jamming of the engine occurs if this has been done incorrectly.")
 
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EYY

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I can't see how it could make a difference providing the rods are symmetrical apart from the locating notches for the bearings. Btw, have you had the rods resized? It's critical when rebuilding these engines.
 

Alcyone

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I can't see how it could make a difference providing the rods are symmetrical apart from the locating notches for the bearings. Btw, have you had the rods resized? It's critical when rebuilding these engines.
The chap at the machining shop said that by habit on these rods, they place the tang (locating notch?) "left of centre" in relation to the crank but really it doesn't matter as, like you said, they are symmetrical. I took the main and rod bolts in and they said they were fine to reuse. I don't think they checked the rods or pins for play though. I know they didn't do anything with them in regards to resizing. I haven't checked them with platigauge yet either. Was kinda hoping they would be okay? The crank got a linish. Main bearings were well within spec when I plastigauged them. So you mean that I really should have the big ends resized?
 
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EYY

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Well, its just that these engines have a reputation for spinning big end bearings when you just replace the bearings without doing any other work. It's because the big ends become slightly ovalled with stress over time, so when you put new (round) bearings in that oval hole, they can have a tendency to grab on the crank. But since you're using a crank with a little more wear/clearance you may not encounter any problems at all. Technically you shouldn't be reusing any of those bolts in the bottom end either, so be careful - don't use the factory torque specs or you'll start snapping bolts.

But, do your own research on those points - I don't want to discourage you. Does your machine shop have much experience in buick v6's? Again, I'm not an expert on these engines, but I've done plenty of research on them myself.
 

Alcyone

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Well, its just that these engines have a reputation for spinning big end bearings when you just replace the bearings without doing any other work. It's because the big ends become slightly ovalled with stress over time, so when you put new (round) bearings in that oval hole, they can have a tendency to grab on the crank. But since you're using a crank with a little more wear/clearance you may not encounter any problems at all. Technically you shouldn't be reusing any of those bolts in the bottom end either, so be careful - don't use the factory torque specs or you'll start snapping bolts.

But, do your own research on those points - I don't want to discourage you. Does your machine shop have much experience in buick v6's? Again, I'm not an expert on these engines, but I've done plenty of research on them myself.
I understand what your saying. All the research I did on forums led me to believe that 'all' the bolts had to be replaced. But the chap at the machine shop said that I only need to swap out the head bolts and rocker bolts. He even said that I really didn't have to swap out the rocker bolts. I got some from MACE anyway. He checked the main bolts but I don't think he checked the rod bolts. If my big end clearances are okay when I plastigauge (even though that's only getting a one sided reading), should I be okay or will only time tell? I guess I can plastigauge a few places inside the big ends can't I. Will do that to check for ovality. Chap also said that he had never seen a block, crank and cam in such perfect nick for the km's its done. I'm really going on what he's told me and what he said he would do if he was to rebuild it himself. This is North East Head Repairs in Wangaratta. They seem to really know their stuff.
I used the factory torque settings twice for the main cap bolts when plastigauging and then finalising the caps onto the crank. Worked and felt real good. Added some oil before hand in case. I've taken everything pretty slow and never gone ahead with anything until I've triple checked it. First engine rebuild too so it's a huge learning curve. I'll also go by feel especially when doing the rod bolts.

Appreciate your feedback here. Every little bit helps. Good thing is having places like this to come to for help and advice ;)
 
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