Vaipulu

Tearing down my 350 my bore measures .040 over

calwldlife

sorry but .040 which is .008 more than a 32nd
ain't workable.
this car ran?

derekderek

Would run. No compression and piston slap would sound like a box of rocks, but it'd run...

68notray

Sounds like Bubba honed the living **** out of it.

All the clearance is on the piston so the bore on a .040 over should be dead on 4.040" top to bottom.

derekderek

Does it have huge ridges at the top of cyls? Years with no thermostat will wear the hell out of the bores.

TimAT

I think I'd double check the accuracy of the measuring tools. And then measure the cylinder in 3 or 4 different spots both the height of the cylinder and at different angles.
A good machine shop, when they bore a cylinder, I think should relieve the bore at the bottom.
And I agree- .040 piston to wall would rattle like a jackass in a tin barn. Not to mention a really short life cycle.

GTR1999

Could be, not that it's correct, but could be.

12-13 years ago my son was rebuilding his 75's 350. We stopped at several automotive machine shops to speak with them. Back then there were still a few machine shops around rebuilding engines, much less today with crates taking over. The shops will good reps had a 3-6 month lead time but were known to do good work. One shop we stopped at I didn't like the guy off the bat, he seemed to lying with every word. I walked out and told me son that guy was a crook, however he said all the things a young gear head would want to hear- they have a dyno, they race their own cars, do a lot of HP work and could bore, hone, hot tank, balance the parts and install my new pistons on the "pink" rods all in a week for $800. To me it was just another Red Flag but my son insisted on using this shop and since it was his car and he was paying I let him make the choice. I figured he would either get a good job or learn a valuable lesson in life.

To make a long story short, the guy was a crook as I expected. He changed the price 2x and the total was up to $1100. He purposely overbored the block 4.036" so my new 030 pistons were no good. The cam bearings were hammered in and burred, and he stole my pink rods substituting passenger car rods in place. I cancelled the check when he told me he knew more about engine building then the engineers at Speed Pro and that I should assemble the engine with the 030 pistons and it would be ok. Ring gaps were double what they should have been and the engine would not have lasted very long. I later found out from other machine shops in the area this guy was well known for purposely overmatching blocks to get future return business. I took him to court over the next 2 years and he settled the night before the trial was to begin. He is still in business and still robbing people, the fact someone didn't take him for a Jimmy Hoffa ride by now is surprising, given the amount of guys he ripped off. I hope you are not in CT looking at machine shops but this can happen anywhere.

Neil B

^^This. You need a dial bore gauge and a micrometer that reads down to tenths. Pistons are not perfect cylinders, they have a taper. The piston needs to be measured at the 'gauge point' with a real mic. In addition, the cylinder needs to be measured at the top, middle, and bottom of the bore in multiple directions.

MotorHead

Nothing short of of a dial bore gauge is going going to give you the correct measurements.

L88Plus

Biggest question - other than your tools - is where you measured the piston. None of the manufacturers I've seen recommend anywhere near the top of the piston. Most are pin sides, about 1" up from the bottom of the skirts, that's where the piston is usually largest.

Vaipulu

Not that I don’t agree with using a dial bore gauge. Let me strap on the flame suit. I can’t stick any real measurement equipment anywhere near a greasy engine. Placing my measurement tools in dirty areas makes my eye twitch. Cough, it’s a disease.... so until everything is clean the calipers is all I can use.


Surly I’m not the only one who’s kept the green felt green.

On that note, if you have green felt in your tool box, please share the cure for the disease...

Neil B

I still keep my mics in their original boxes setting in a lined toolbox drawer. Now pull those tools out and use them. They will clean up great with a microfiber towel.

Neil B

Yep, 'gauge point' for most pistons is on the skirt at approx. the height of the pin from the bottom.

TimAT

And at 90* from the pin bore. As seen in the picture.

derekderek

They are also sometimes narrower where the rings are. I have a set of .010 pistons that fit a standard boreright to the bottom or the oil ring. I use one as a quickie bore gauge to tell if a 454 is standard or over.

bashcraft

Its called a rag.

This is the lamest excuse for not doing something that I've ever heard.

68notray

"Sometimes narrower where the rings are" ?
Pistons are ALWAYS narrower everywhere but the part of the skirt 90 degrees from the pin. They are barrel shaped by design.