Bearing Clearances

[Dale FZ1]

I want to have an idea of what range the various clearances should be at when screwing together the RB30 bottom end. So to those who have solid, experience based opinions, could you give an indicator of

Mains

Big ends

Thrust

clearances that should be the acceptable range? As an amateur builder I'm interested to see what others chase.

Engine to be set up for street + occasional track, RB26 oil pump, head feed restrictors, 6500 limit and ~ 15-16psi boost. Stock rods and +0.5mm cast 30E pistons.

[Adriano]

Proengines recommended .003"-.004" (.075-.1mm). thrust

[GTR1993]

this will depend greatly on who you ask, what oil you will run etc. Some people will recommend building them tight, near 1 thou on the mains, others will say 2 thou on the mains, general rule is 1 thou per inch of journal, and the more power you wake the larger the clearance. Personally i have built some sr20s loose, 2+ thou on the mains and was fine. I don't think there is the perfect rule, but building them a little on the looser side makes some sense to me.

[T04GTR]

standard thrust of about 3-4thou

mains around 2 and bigends around 1.5-2. if youve got a big hp and high rev motor, add .25 thou.

this is using a standard wieght oil. ie 40-50 hot.

the bigger the clearance the, the bigger the oil pump needs to be. also the bigger the clearance the less the oil will heat up

all the engins ive built have 1.7~ bigend and 2~ mains and 4~ thrust. (with a light leverage when checking. not just pushing with your hand)

[Dale FZ1]

Cheers Dave, good info that makes sense. I expected that the pump delivery should be geared to the bearing clearances, and what you say is logical.

I'm relying on the ability of my machinist, but want to be sure I'm going about it the right way. Somewhere I'd seen a comment advising against the use of plastigauge to check journal clearances during a dummy assembly. Anyone care to advance a reason why?

[GTR1993]

I think it is just less accurate, i use a dial bore indicator and works well.

[r33_racer]

Less accurate and easily influenced by foreign particles. Internal and external Mic's the way to go! Three point variety too(for internal) if you can afford them.

[T04GTR]

i use the plastiguage way. but you have to be carefull. the main problem is the crank spinning, and the dowls locating the conrods can grab and squash it more when you knock the caps off to check them...

works great for mains but. oh and i use a dial indicator for thrust. feeler guages is just not as spot on... as you actually have to push on the crank to get the best reading.

ie: 4 thou with feelers would be 5 or 6 or with a dial indicator.

ps, getting the girdle to sit in the right spot takes a while with a plastic hammer moving it back and forth so the thrust bearings are both contacting the thrust side squarely.

from experiance a well maintaned crank without scoring, given a light linnish tends to end up aroung the 1.5-1.7 range. but its imperative that you have the crank grubsrewed when its at the shop ,so you can actually clean it out properly before assembly.