Oversize Pistons

[Racer X]

Why not the flywheel?

The flywheel, crank and damper are usually balanced together, and having the clutch cover with pressure plate balanced at that time is something that should be done.

The pistons will need to be fitted to the bores. When you use, say, twenty thousanths oversize pistons, the piston is measured and the cylinder bored and honed to fit that piston. Each one is fitted and marked for the bore it was fitted to. Then the connecting rods are checked for squareness and that the pin and journal bore centerlines are parallel, the pistons fitted to the rods, then the assemblies are weighed, and if needed, material is removed until everything is within a tolerance (I forget right now how close is considered the same).

This is all very important stuff, especially for an L series six cylinder, as the crankshaft is quite long, and vulnerable to torsional twisting fatigue under load.

Are you looking for cast pistons? Forged? Billet?

 

Also, keep in mind, engines usually only have enough cylinder wall thickness to go two steps overbore. You've alread taken one cut. It is fresh. It is starting to sound like sorting this out by taking another cut is going to cost more than having pistons made, to fit the overbore you have now. Search the innerwebs for custom made pistons. JE is one I know of, although I have not used their services.

 

 

 

 

 

 

Edited July 1, 2022 by Racer X

[ArcticFoxCJ]

So I contacted the machine shop and they actually offered to bore it again at no charge.  I guess since I JUST had a bunch of work done.  I also ordered the pistons from Greenline.  They say they're backordered until November, sadly...  But it is what it is.  In the meantime I can focus on the car's body and other systems.

[dutchzcarguy]

8 hours ago, Racer X said:

The flywheel, crank and damper are usually balanced together,

I'm NO engine builder but i think that's tipical american (engines) way to think..  Japanese engines are balanced per part i think?  The inner parts are balanced maybe together i don't know but the flywheel/clutch is balanced separatly for as far i know on these japanese engines?  

Maybe im wrong, i never had to repair a underblock of these engines..

(I also ask myself how a machine would look like that could make a balance in a engine when it's all bolted together?  I have heard of balancing the cranck and the connecting rods and pistons are weighed, but no flywheel as it is balanced on it's own..)

 

[Racer X]

53 minutes ago, dutchzcarguy said:

I'm NO engine builder but i think that's tipical american (engines) way to think..  Japanese engines are balanced per part i think?  The inner parts are balanced maybe together i don't know but the flywheel/clutch is balanced separatly for as far i know on these japanese engines?  

Maybe im wrong, i never had to repair a underblock of these engines..

(I also ask myself how a machine would look like that could make a balance in a engine when it's all bolted together?  I have heard of balancing the cranck and the connecting rods and pistons are weighed, but no flywheel as it is balanced on it's own..)

 

 

An engine is an engine, cast iron, steel and aluminium. Doesn't matter if it was made in Japan, US, Europe, Mexico, Brazil, or China. The principles are the same.

Sure, the rotating assembly can be balanced as a whole, or separately. But it is always better to balance those items I mentioned as a single unit. The damper is keyed to the crank, so no need to mark it for reassembly, the flywheel and clutch cover are not, so the must be marked for reassembly to the orientation they were in when the assembly was balanced. After the machining of the crank is done, the machinist I have used assembles the flywheel, clutch cover and damper to the crank, performs the balancing work, then disassembles it all.

The piston and rod assemblies are balanced by bringing the weight of each assembly as close as is possible to eac of the others. 

 

It doesn't matter what language the manufacturer speaks, the materials and processes are the same.

 

 

 

 

 

[dutchzcarguy]

7 minutes ago, Racer X said:

But it is always better to balance those items I mentioned as a single unit.

Yep... that's were i totally agree..

About the marking of a flywheel... i Neverrrr marked a flywheel or clutch assembly on a Datsun..  I'm almost sure never have read this in ANY servicemanual of the Nissan datsuns i repaired.. and i have all the serv.man. of my cars, i don't work on any car without a service manual..  something i really really!!!  advice anybody to do because your doomed to get things wrong.

Haha.. makes me think of this: like the guy VINNY from american shopper once said:  I CAN NOT EMPHASIZE HOW MUCH YOU CAN NOT DO THAT!  (He was using a acetylene burner IN a harley block to get rid of a bolt..or something like that!   hahaha) 

[ArcticFoxCJ]

In a perfect world, all parts would be balanced as one.

In this world that's not going to happen in my case.  Why not the flywheel too?  Well to be honest, because I don't care.  I used to be an ASE Certified Master Tech, and I even worked at Nissan dealerships and I can tell you that in times we had to pull the flywheel from vehicles, they went right back on without necessarily being at the same clock position as they were when they came off.  The part is indeed balanced by itself.  I'm sure you 've noticed there's sometimes a weight welded to the flywheel somewhere.  That's why.  We didn't worry about putting it back in the same position because it just doesn't matter on these.  

Argue that point if you like, but never once did I or any tech in the shops where I worked have a problem or a comeback when doing this.  

My flywheel is going to get taken to the machine shop to be resurfaced and cleaned up, but I'm not concerned with balancing it with the assembly.

Now admittedly I have little experience in tearing down engines and reassembling them in a shop environment because when we had internal engine problems we'd replace the engine at the dealership.  Regular repair shops just don't get into that kind of work.  It's a shame, but again, real world vs. perfect world.  The last time I did anything like this was on an '87 Jeep Wrangler with a 4.2L inline six.  And that was... a while ago.  It turned out fine.

I'm building this 280z on a budget, and I'm already over $3k in just this engine and I'm not even done yet.  I wasn't expecting to completely teardown, machine and rebuild it when I got the car but yet again, real world.  Decisions have to be made.  If not balancing the components together bites me in the backside later then it bites me in the backside.  The project is being funded by eBay sales and mad money out of my paychecks so this kind of compromise gets made because the alternative is that my grandchildren will be finishing the project for me.  

Some, including people with more experience in engine work may disagree and I respect that, but this is where I stand on it.

[Racer X]

4 hours ago, ArcticFoxCJ said:

  I used to be an ASE Certified Master Tech,

When I was still working as a journeyman mechanic at the local electric utility I held ASE Auto and Truck Master certification, and was a certified Mobile Fluid Power technician (hydraulic systems).

 

4 hours ago, ArcticFoxCJ said:

  I'm sure you 've noticed there's sometimes a weight welded to the flywheel somewhere. 

Can’t say that I have ever seen additional weight added to a flywheel for balancing. I have seem where material was removed, by drilling.

[ArcticFoxCJ]

8 minutes ago, Racer X said:

Can’t say that I have ever seen additional weight added to a flywheel for balancing. I have seem where material was removed, by drilling.

Yeah I've seen that too.  I don't know if the difference is by manufacturer, or era, or place or something else.  Might be an interesting thing to look into.  Seen it done with torque converters too but not as often.

[Racer X]

1 minute ago, ArcticFoxCJ said:

Yeah I've seen that too.  I don't know if the difference is by manufacturer, or era, or place or something else.  Might be an interesting thing to look into.  Seen it done with torque converters too but not as often.

I have seen it on torque converters, and driveshafts.

[Patcon]

I don't think that not balancing is going to cause a failure. I just think it makes the motor rev smoother. I remember when my rear view mirror would vibrate when I really spooled up my Z. That was way back when I had one that ran...😉