Help, main bore & crank dimension specs on 109?

[Turboholic87]

Was checking the main bearing clearances today and found them to be 2.5-3 thou. I'm using a new cat crank & Std. FM 107M 3/4 groove bearings. My machinist quoted me .0018 when I asked him but who knows how well he checked the clearance.

The block was line honed with a girdle and I'm wondering if the bores are too loose which would mean the bearing crush is insuficient. I used a dial bore gage & plastigage with the same results. Crank mains measure out at 2.4994-2.4993 which is very close to the Hayes manual spec of 2.4995.

Am I missing something or just making a big deal and should run with these clearences? What should the main bore diameter be and how can I check proper crush? Any info would be helpful.

Thanks,
Greg

 

[turboclam]

There are many opinions out there about clearances. I think anything over .025 is too much for a street car. Did the machinist drill out larger holes in #2 and #3 mains? If you have a girdle then I would guess it's going to be a street/strip car. I personally run a 95% street car with .025 on the mains with the main center holes drilled out. 8000 miles on the motor and a couple trips down the track with no problems. Hot oil pressure is 12-15lbs running 10w-40. I don't know if they make a bearing that would help fill in the extra space you have or not. I went through this a about 4 years ago and decided to custom cut a crank so it would tighten it up for me. I'm sure you'll get some more opinions on this.

 

[turbofabricator]

Order .001" undersize bearings and swap out only the one half or both to get your clearances between .0017"-.002" Real common to swap bearing halves to get clearances where you need them. If the line hone is too large, you "can" use a strip of aluminum foil between the bearing shell and the journal (block). Yes, it does work. Just be real careful in ensuring you don't have any wrinkles in the foil. If you pull the engine apart after using alumium foil behind the bearing shell, you will not be able to even see the foil. It becomes part of the shell over time. (don't use heavy duty foil unless the clearances are WAY off. Then you should have the journals re-machined.)

 

[gnsrule]

Does anyone know or have a link to the specs for main bore size ? Same for rod big end size. Crank and rod jrnl specs too.
Thanks again

Craig

 

[Jerryl]

Does anyone know or have a link to the specs for main bore size ? Same for rod big end size. Crank and rod jrnl specs too.
Thanks again

Craig

Is this what you are looking for?
Factory Engine Specification

 

[dr_frankenstein]

Order .001" undersize bearings and swap out only the one half or both to get your clearances between .0017"-.002" Real common to swap bearing halves to get clearances where you need them. If the line hone is too large, you "can" use a strip of aluminum foil between the bearing shell and the journal (block). Yes, it does work. Just be real careful in ensuring you don't have any wrinkles in the foil. If you pull the engine apart after using alumium foil behind the bearing shell, you will not be able to even see the foil. It becomes part of the shell over time. (don't use heavy duty foil unless the clearances are WAY off. Then you should have the journals re-machined.)

OMG your an F'n genius.

Thank you.

A.j.