Help with bore size.

[1twistdtalon]

i picked up a block from a guy 4 years ago and can not find him now to see what he had done to the block. I think he had 2g Pistons in the 6 bolt block and the big 1g rods in it. But now I'm pulling it apart to put forged internals in it and I can not figure out what Pistons it has. I calipered the bore at 85.727? Is that a stock bore? It seems larger then stock.

 

[BogusSVO]

Stock bore is 85mm or 3.346

85.5mm or .020 over would be 3.366

85.75mm or .030 over would be 3.376

86mm or .040 over would be 3.386

Now your 85.727 is 3.375

So you are a .030 over (tight by .001)

.75mm/.030 over is an odd bore size for the 4G63, most pistons are .50mm/.020 or 1mm/.040 over

 

[1twistdtalon]

That's what I was thinking Iv never seen anything but. Standard bore, .20 and .40 over. Would I bet better going .10 more over? To make it a more common bore and make finding Pistons easier ?

 

[BogusSVO]

That or find another block and go .020

 

[1twistdtalon]

I do have another stock bore block... Thanks for the great help and fast reply .

 

[BogusSVO]

.040/1mm over is just fine for a stock rod build.

But if going forged piston/Hbeam rod I rather have the bit of extra meat in the bore and go .020

Just my preference.

 

[1twistdtalon]

That was my next question. I will be running a new crank and eagle h beam rods... My standard bore block I have and with the new crank it is out of spec. May have to go with over sized bearings.

 

[tmoney20g]

My standard bore block I have and with the new crank it is out of spec. May have to go with over sized bearings.

If you're going to build power at some point, DO NOT go with 10-over on a cut crank and oversized bearings. Again, go find a nice crank from an n/t or something.

 

[1twistdtalon]

So your saying I need to find a inspec block? My crank is brand new out of the box. It would be the mains that are out of spec? Or am I wrong there.

I wonder why the other guy would have went with a .30 over bore and not something more common..

 

[tmoney20g]

The mains don't wear, the bearings/crank do. Not sure how mains can get out of spec since nothing touches them ?

Mitsu used to offer oem spec pistons in 10, 20, 30, and 40 sizes for rebuilds.

 

[1twistdtalon]

That makes sense. No friction no wear . I Must be miss remembering I did put that block together 12 years ago. I know i ordered a new crank for it and I swear I had to use .10 over bearings on it . I'll ha e to check it once I tear it apart anyways.

Id rather go with a forged piston.

 

[tmoney20g]

Hrm, not sure why you'd have to use 10over on a brand new crank. My block, upon inspection, had 10-over bearings and a cut crank for the mains, same with the rod journals. So that crank is sitting here in a corner, punished. I found a nice crank on ebay, that was in-spec, for my current build; notes on that are probably around page 2-3 of my build journal.

 

[1twistdtalon]

Ya I very well must be off on that. I'll have to get the motor in my shop and open it up and check it all and see what I have for options. I'll have to take a look at your build .