Bottom end on TAFC

bottom end on alky motor

generally for quick service in between rounds, a team will have several sets of top rod bearings ready to go. those will be rotated out of the motor to be measured and cleaned up. to service the bottom end quickly, you really don't have time to measure, clean and put them back in, that's why you have a set ready to go in..then measure afterwards.

we keep a log of bearings going in and out. the bearings are measured before the run and after to accurately determine how much it 'squashed' a bearing. this measurement is taken after scraping the excess babbet off the sides of the bearing.

i notice a lot of teams don't measure the end to end clearance on the rod bearing, but it's a useful measurement to follow. today, most teams run the harder V style bearings, which won't get beat out at the bottom unless you're really hammering on it. however, you'll see it start to lose end to end measurement. it's also a sign of when you need to take that bearing out of service. on a v bearing, if it's starting to get below 2.503, then it's been beat on, or it's just getting too many runs on it. if it comes out 2.498 or so, i'll take and bend it out just a touch applying pressure outward from the very base of the bearing. you just have to use judgement (and your log) to determine if it's tuneup or just runs. the reason for measuring this is the rod journal is 2.500. if it isn't a little bigger, it isn't going to have much tension in the cap. thus, it's more prone to spin.

also you have to look at the surface to see if it's moving metal or not...the fingernail test is the best way to see if a bearing is good to go back in the motor or not....if you can't scotchbrite any ledges off, chunk it. when in doubt, chunk it. bearings are cheap, cranks and blocks are expensive. hate to kick the rods over trying to get one more run on a bearing.

in my opinion keeping fresh bearings in a motor is the only policy to have regardless of budget. if you're on a tight budget, it should be more the reason to keep fresh bearings in it to extend the life of the really expensive parts. if you have a decent budget, then you don't have an excuse.

the bearing program i had on cannons car and our car now -

1. change/check upper rod bearings every pass (if it at least makes it to top of low)
2. change lower mains every 2-3 passes (usually at night after day is over)
3. change upper mains every race
4. change bottom rod bearings upon inspection...inspect between races to insure sufficient end to end clearance.

RE: No. 2. - On a tighter budget, you can get by with just checking the lowers, and if the bearing looks good, has good tension in the main cap, then it's safe to run it. however, if you put fresh lowers in it, then you can run eliminations and not worry about how the mains are holding up.

the above program might run you a higher bearing tab, but will make your crank and block tab a little lower.

NOTE to teams still running the soft M bearings - RACER BEWARE - it used to be all you had to look out for was the notorious 8/00 batch of M bearings. i started running our car in licensing with M bearings with the theory of getting the tuneup right with the soft bearings and then switching to v bearings. with a very mild tuneup - i had several m bearings try to delaminate on me - and not from the notorious 8/00 batch. several were on the verge of blackening the crank. i talked to several other teams and tuners and i was not alone. it's my advice to stay away from the m bearings, change to v's (rods and mains)....and measure your tuneup with end to end clearance like mentioned above. if you're not a fan of a hard thrust bearing, king makes a softer thrust that has done well....however i wouldn't recommend king rod bearings in a competitive top alcohol motor.

hope that helps...

 

stay away from the M

I would only run V bearings and hire a good tuner. If you don't have the money now, wait till you do. It will be a lot more fun, and cheaper in the long run. I know that's easier said than done.

 

note

the above bearing program was for a screw blower alcohol team winding it up 9500 rpm +

if you have a roots and are turning it that high, you probably need close to the same program.

blown1020 - in between rounds i would check the oil filter and make sure the oil isn't too polluted. i would rotate in a fresh set of rod bearings every race, and check the lower mains. if they look and measure good - and have tension, i would continue to run them.

no matter what you run, bottom end is PREVENTIVE maintenance. everything else may be fine, but there may be a bearing that's not happy. regular bottom end maintenance may catch a problem before it becomes a large one. winners stay on top of their maintenance and do the things you 'probably don't have to.'