Piston Ring Gaps (Standard vs. Max)

[Careless]

Posted this over on z31performance. just looking for some opinions.

 

Hi Gents,

 

So I'm assembling the engine in the garage on a piece of plywood on the floor for now. My VG30ET is taking up my engine stand and to be honest, I like sitting on the ground rather than standing for this long.

 

I am dealing with a GAP headache here.

 

VG30ET specs:

 

VG33E specs:

 

VG33ER specs:

 

My initial values for the top rings (haven't checked bottom or oil rings/expander yet) are close or about 0.58mm. That's already passed the MAX gap for the VG33E, but lower than the MAX gap for the VG30ET (which seems a heck of a lot higher, 1 full millimeter!).

 

My worry comes from whether or not the machinist bored the pistons out to the proper size, but when I asked him what value he used, he said he honed them to the final size on the outside of the Sealed Power piston box (which I was hoping he would say).

 

I don't have the proper tools to check, but the pistons are pretty snug in here. Should I be worried if the boosted motor has a higher ring gap then the non-boosted one, and mine is lower than the MAX specified for the boosted motor? lets face it... no one is going to put these pistons in a Quest. It must have been made for a supercharged or turbocharged motor. but the gaps are smaller there...

 

I need to have the piston ring gap finalized before I assemble the pistons for final insertion. Then I can check the rod journal sizing. I'll be taking a couple of hours off work tomorrow to check that out. More to come!

 

Also, I got the main bearings torqued. All the values written down. Everything is well within spec, and it's ground and nitrided. Looks like a brand new crank. The journals are beautifully polished and my plastigauge says no journal taper at this point. Fillets obviously look smaller due to grinding, but if they're in spec, they're in spec!

 

NOTE: Check the front and middle two main bearings, the front bearings are about 2 or 3 mm wider to take more load thanks to the increased surface area that will get a wider oil film to help offset the tension of the timing belt and the accessory drive. The center ones seem like they're just there to just ride the wave with the wider rear and front bearings.

 

EDIT: I meant to say i hoped he would say he went by the box. error on my part.

 

but perhaps he took the piston measurement and the FSM clearance range, and subtracted what he got from the pistons and honed each cylinder to the proper ring clearance. He didn't assemble the bottom end so he would not check ring-gap in that case...

 

so I'm not sure if i should be worried.

 

I managed to get every ring gap to the same feeler gauge blade for each type of ring. I succeeded in getting the following readings from every ring gap by swapping them around:

 

Top Ring: 0.58mm

Middle Ring: 0.58mm

Oil Control Rings (Top & Bottom): 0.75mm

 

 

I don't know if I should check the Expansion Ring... or how?

 

Which means I'm close to the VG30ET readings on the oil control rings, so maybe it means the ring set I got was over-cut in size.

 

Is it because it's a turbo motor, and the E and ER are not exactly the same? (heat issue here? not sure..).

 

so that means I'm calling Federal Mogul to make sure. and then call him to ask him what he did.

 

 

My only option is to run it as is. But I just want to know.

 

What's weird is that they also have 1.00 mm oversize rings but they don't offer the 1.00mm piston anymore (or if they ever did... but i see it listed some places).

 

So if I were to get rings that were 1.00mm instead of 0.75 mm... perhaps it would close the gap to well within reasonable specs?

 

I'm not sure if you can do that... 0.25 is less than the gap size it's trying to close in on... but the logic isn't quite the same when mixing those two measurements...

 

Should I order rings in the larger size and see what works and return the ones that are over-gapped? Not sure how smart that is... but perhaps someone has had success doing that assembling engines that I don't know of?

 

Now it comes down to getting larger rings and trying them out or going with over-gapped rings. Those are my two options. Looking at specs for turbo and or nitrous 350's and such (and I know, it's a horrible comparison, but I'm going to do it anyway)... they run 0.02 to 0.03 inch gap, or more!

 

Heck the toughest thing in engine building is having to decide. LOL.