Marks from rings in bore after piston install?

[rabbitman]

The pros on here all say that boring it bigger than spec is about like starting out with a half worn block and any machine shop that doesn't want to do it to bentley specs should be avoided.

[maxfax]

The pros on here all say that boring it bigger than spec is about like starting out with a half worn block and any machine shop that doesn't want to do it to bentley specs should be avoided.

Indeed..   The idea behind the looser spec for performance is simply to reduce friction..  Pretty much like is done in GASSER race motors..  However, since a diesel needs that compression the tighter, the better it's gonna last...

[rabbitman]

The pros on here all say that boring it bigger than spec is about like starting out with a half worn block and any machine shop that doesn't want to do it to bentley specs should be avoided.

Indeed..   The idea behind the looser spec for performance is simply to reduce friction..  Pretty much like is done in GASSER race motors..  However, since a diesel needs that compression the tighter, the better it's gonna last...

and diesel fuel is a lubricator anyways.......at least it used to be.

[DJPyro]

Actually most gassers that run a lot of piston clearance are using forged pistons which expand when they heat up. If you ever listen to a motor with forged pistons start up, they'll have massive piston slap for the first few minutes until things start to heat up and it will gradually diminish as the engine comes up to temp and the pistons expand.

[kevinm]

DankCorry why the concern... Have you got your motor up and running yet and had low compression?

[sdwarf36]

The pros on here all say that boring it bigger than spec is about like starting out with a half worn block and any machine shop that doesn't want to do it to bentley specs should be avoided.

 Show me an engine thats worn an exact amount the full length of a cylinder-and in all axis's.  And give me the address for Bentley warrenty claim center. 
 If you bring me stock VW replacement pistons-I'll feel safe giving you .001.
 If you bring me Mahle's-I'd do it-but give you plenty of warning why I'd be worried.
 If you bring me Prothe pistons made in some country i never heard of-I'd make you sign something that you know more about the thermal expansion quailties in a piston that only costs a 1/4 of stock-and you trust your judgement over what pros in the trade have seen time+ again.
 Scuffed pistons suck. And if it happens, its ALWAYS the machine shops fault.  NEVER the customers.

Don't lose any sleep on your .0015 clearance-its what I built my own engine to.

[dankcorey22]

DankCorry why the concern... Have you got your motor up and running yet and had low compression?

Nah man just the bottom end im in school now totally away from where my engine is. ill finish it this summer. Im kinda worried now since this discussion  about low compression

[maxfax]

I'm with sdwarf, don't loose any sleep over it..  I've simply thrown a set of rings at engines approaching the half million mile mark, and get a few 100,000 miles out of them with little trouble..

[sdwarf36]

.0005 in bore size equates to .0015 more ring end gap-don't lose sleep. And people seem to take the .003 number as a "fail" number-what it means is "you started with .001-you now have.003--so your cylinders have worn .002 from where you started."

[R.O.R-2.0]

The pros on here all say that boring it bigger than spec is about like starting out with a half worn block and any machine shop that doesn't want to do it to bentley specs should be avoided.

Indeed..   The idea behind the looser spec for performance is simply to reduce friction..  Pretty much like is done in GASSER race motors..  However, since a diesel needs that compression the tighter, the better it's gonna last...

and diesel fuel is a lubricator anyways.......at least it used to be.

yes, it did USED to be..

i found some old high sulfur diesel not too long back, about 3 gallons of it, ran my car till it was about out of fuel then dumped in the HSD, and as i was fueling the car (with the engine running) i could hear it clattering less.. and it felt like it had a slight power increase..