Engine info - something new I learned

[lee]

Maybe you folks all knew this...I didn't.

Seems Subaru does not necessarily install the same sized pistons from the factory in any one given engine. Now maybe I'm wrong, but I think this is a pretty unusual practice. Does this work because of the inherent balance of the boxer engine?

Anyway, I post this as a caution for anyone thinking of a home rebuild...also might want to provide the info to whatever rebuilder you use if having the job done professionally. Seems like it would be of interest to those balancing/blueprinting as well.

So for you shade tree mechanics, watch which cylinder the piston came from...my reference is:

http://www.endwrench.com/pdf/engine/...esInfoSp00.pdf

[SVXer95]

Do they match-grind the piston and bore?

[svxsubaru1]

So ever cylinder has a diffretn size piston? I never heard of this before, who told you this?

[lee]

Originally posted by svxsubaru1
So ever cylinder has a diffretn size piston? I never heard of this before, who told you this?

Not necessarily, click on the reference and read Subaru's own words

[svx_commuter]

This is clearly stated in the FSM. The pistons are given a grade letter and then the letter is stamped on top of the engine block for each piston. The clearance between the piston and cylinder is very tight on the SVX. That is why the piston has to be matched to the bore. I think it also a good part of the reason as to why the engine is so quite.

Subaru has been doing this for a while now on all its models. The "grade" of piston and its location in the block is stamped on the top front of the block. You can not mix and match.




Dave

[SVXRide]

Probably a major reason why the engines last so long -- looks like we get a blueprinted engine from the factory!
-Bill

[wawazat??]

Originally posted by SVXRide
Probably a major reason why the engines last so long -- looks like we get a blueprinted engine from the factory!
-Bill

According to the R&T guide, each EG33 was also dyno tested prior to mounting in the car to ensure performance.

[oab_au]

The bore and piston sizes vary with manufacturing tollerances. Most engine builders selectively fit pistons to bores. Some selective fit crankshaft, slipper bearings also.

Harvey.

[SVXer95]

Originally posted by wawazat??


According to the R&T guide, each EG33 was also dyno tested prior to mounting in the car to ensure performance.

Yet another reason why so few were made and the price was so high....

[svx_commuter]

Now I got the FSM here in front of me. The clearance is .0004 to .0012 inches diametrical.

Bore size Piston Grade/ Cylinder bore / piston sizes follows:
A 3.8151 to 3.8155, 3.8144 to 3.8148
B 3.8148 to 3.8151, 3.8140 to 3.8144
C 3.8144 to 3.8148, 3.8136 to 3.8140

I wonder if they did this on the piston slapping 2.5 engine?

[SVXer95]

Originally posted by svx_commuter
Now I got the FSM here in front of me. The clearance is .0004 to .0012 inches diametrical.

Bore size Piston Grade/ Cylinder bore / piston sizes follows:
A 3.8151 to 3.8155, 3.8144 to 3.8148
B 3.8148 to 3.8151, 3.8140 to 3.8144
C 3.8144 to 3.8148, 3.8136 to 3.8140

I wonder if they did this on the piston slapping 2.5 engine?

Wow, six tenths max clearance. Not bad, not bad at all.

[lee]

Originally posted by oab_au
The bore and piston sizes vary with manufacturing tollerances. Most engine builders selectively fit pistons to bores. Some selective fit crankshaft, slipper bearings also.

Harvey.

Harvey, I haven't wrenched professionally since 1972, and that was on traditional American iron. I can assure you that in my part of the the US there was no piston matching 30 years ago - except maybe for serious blueprinting work. Although with the advent of Plastigauge, there was some crank/rod bearing matching by the better shops and by most hot-rodders.

Are you saying most auto/engine builders do this today, i.e., Toyota, or is this something modern, and good, rebuilders do?

[SVX-FF]

Originally posted by svx_commuter
Now I got the FSM here in front of me. The clearance is .0004 to .0012 inches diametrical.

Bore size Piston Grade/ Cylinder bore / piston sizes follows:
A 3.8151 to 3.8155, 3.8144 to 3.8148
B 3.8148 to 3.8151, 3.8140 to 3.8144
C 3.8144 to 3.8148, 3.8136 to 3.8140

I wonder if they did this on the piston slapping 2.5 engine?

On grade A you are looking at a .0003 thru .0010 tolerance
On grade B you are looking at a .0004 thru .0011 tolerance
On grade C you are looking at a .0004 thru .0012 tolerance

those are pretty tight to hold on a cars engine. That is very impressive considering that a human hair on average is .0035 thick.
No wounder the EG33 runs so smooth.

Steve

SVX-FF, what's with you and the cicadas?