Main bearing clearances???

[Ricochett]

Can i get ya'lls opinion:ugh on my main clearances

on my 427 i bought after market connecting rods as well which will go
to 7500,RPM my rod clearance is .001 as well

 

[Hib Halverson]

Hard to see the numbers in that image but your Rat is going to do best with .002-.0025 on the rods and 0025-.003 on the mains. Less than those numbers would be risky.

Keep in mind that Plastigage is not quite as accurate as precision measuring equipment.

Lastly, those rods might go to 7500 but to get the rest of the engine to be able to rpm like that safely and at good power levels is going to run you some serious money in pistons and valvetrain, not to mention cylinder heads.

 

[Ricochett]

Hib
Thanxs for the reply im averaging .015 to .001 on my mains as well as my rods
and i also didnt mention that i bought forged pistons had the motor balance and going with a roller cam
Thanxs Hib

Joe

Hard to see the numbers in that image but your Rat is going to do best with .002-.0025 on the rods and 0025-.003 on the mains. Less than those numbers would be risky.

Keep in mind that Plastigage is not quite as accurate as precision measuring equipment.

Lastly, those rods might go to 7500 but to get the rest of the engine to be able to rpm like that safely and at good power levels is going to run you some serious money in pistons and valvetrain, not to mention cylinder heads.

 

[Peer81]

Not to attack you on your project but I'f your building an engine to go to 7500 rpm it's all in the details. I don't know if you have some quality measuring tools (analog or even better digital) but you need them to make this engine a succes.

Good luck!

Greetings Peter

 

[Hib Halverson]

Hib
Thanxs for the reply im averaging .015 to .001 on my mains as well as my rods

Keep in mind that Plastigage is not very accurate–at least not in the perspective many use when checking clearances in a street high-performace or racing engine–but if you're going to use Plastigage, I'd either have the crank polished to take about a thousandth off all the journals or go to .001 oversize bearings

and i also didnt mention that i bought forged pistons had the motor balance and going with a roller cam

What's the cam profile, what springs are you going to run and what's your rocker arm package?

 

[TimAT]

Those clearances are really tight- even on an engine that will never see 5000 RPM much less 7500. I'd have to suggest that with the clearances that small it would be a good candidate to spin bearings. You won't be able to have enough oil film on the bearings to protect them.
I've seen new engines from Chevrolet that had a .015 undersize rear main bearing just for a little help with leak control, but the engine still had .002 on that bearing.

 

[Tom Bryant]

I agree. That's pretty tight. As for Plastigage; I don't like it, I don't use it, never have and never will. Buy or borrow some quality mics and get a proper reading. Then you will know for sure what your clearances are. It sounds like you are building a serious engine so don't short cut the measurements.

Math is fun.

Tom

 

[JohnZ]

Clearance as shown in the photo is WAY too tight; mic the parts to verify them and post the results. At .001" (or slightly less) you're going to go metal-to-metal and spin bearings.