Rb26dett Oil Clearance Question

[Guishnu]

Hey Folks,

I was wondering if one of the hotshot engine builders on here would give me some advice. Im in the process of doing my very first full/ground up engine build and im having some issues with oil clearances. I am using plastigague as a measuring tool and I want to double check im doing it correctly. The plastigauge "splat" matched up to the card between 0.050mm and the 0.038mm marks giving me an estimated clearance of around 0.046mm (ish) do i then divide that figure by 2 to give me the actual clearance of 0.023mm? IE: Bang on the Nissan spec of 0.022-0.046 mm??

Or is my actual clearance 0.046 (ie: on the very limit of the OEM specs)

I think im right that the plastigauge figure has to be divided by two to account for the two oil surfaces (one on each side of the crank) but i just want to be 100% sure.

I measured the BE bearing and that came out at dead on 0.050mm which if i divided it by 2 would be bang on spec, but if it's not then i think im way out.

The engine is an R32 RB26DETT with a brand new ACL standard size bearings. Crank has been polished and nothing else.

Cheers

Chris

Edited February 24, 2010 by Guishnu

[STATUS]

If your engine is upside down the crank is fully rested against the bearing material on the low side so your measuring the clearance on the high side (sum of both clearances) no need to divide by 2.

That said i no longer (since i was an apprentice) use plastigage as it is not precise enough, it will often read tighter than it actually is giving you a loose engine. A mic is the only way to go TBH

see stolen interwebs picture.

[The Dan]

I am using plastigague

Problem #1

[zebra]

care to explain what a "mic" is trent? never heard of it before...or maybe i have under a diff name?

[zebra]

care to explain what a "mic" is trent? never heard of it before...or maybe i have under a diff name?

[The Dan]

A micrometer. for measuring the crankshaft and tunnel sizes. You need internal and external mics to do the job accurately

[The Dan]

[zebra]

ah right...i knew it had to be simple...i agree that the micrometer is a much better way of doing it..

[Swiper the Fox]

mic first...plasti second.

yep thats right...i measure twice...using each method.

I know of an engine that failed very recently that would have been saved if the builder used this method, as the plastigage would have picked up the huge error in his micrometer.

its just a good double check of the micrometer measurements and its not as inaccurate as one may think if used correctly.

[The Dan]

mic first...plasti second.

yep thats right...i measure twice...using each method.

I know of an engine that failed very recently that would have been saved if the builder used this method, as the plastigage would have picked up the huge error in his micrometer.

its just a good double check of the micrometer measurements and its not as inaccurate as one may think if used correctly.

Not disagreeing with you here Paul, and anything that works for you has gotta be a good thing as you build a mean engine.

The example you provided with the micrometer having an error? If measured properly and the micrometer calibrated correctly and the engineer all doing their job correctly, any error in a micrometer can be picked up without needing plasti gauge to back it up.

If you use the same micrometer for the journal measurement as you do for the tunnel measurement, the micrometer doesn't even have to be accurate, it just has to be consistent.

[Swiper the Fox]

Not disagreeing with you here Paul, and anything that works for you has gotta be a good thing as you build a mean engine.

The example you provided with the micrometer having an error? If measured properly and the micrometer calibrated correctly and the engineer all doing their job correctly, any error in a micrometer can be picked up without needing plasti gauge to back it up.

If you use the same micrometer for the journal measurement as you do for the tunnel measurement, the micrometer doesn't even have to be accurate, it just has to be consistent.

Using just plastigage and nothing else is folly in the extreme...i understand exactly what you were saying and also what you have just said above. Im assuming the tunnels and the journals must have been measured on different equipment or even different days? It didn't sound right to me but that was the excuse he provided to the customer.

A quick check of mic. calibration with the setting bars is also a good idea each time it is pulled out of the case as well.

the engine in question had a huge knock on startup...big mistake that could have been easily picked up.

Edited February 25, 2010 by DiRTgarage

[STATUS]

mic first...plasti second.

yep thats right...i measure twice...using each method.

I know of an engine that failed very recently that would have been saved if the builder used this method, as the plastigage would have picked up the huge error in his micrometer.

its just a good double check of the micrometer measurements and its not as inaccurate as one may think if used correctly.

Not a bad comparo, some one pm'd it to me today (mirrored what i was saying earlier)

http://www.carcraft.com/techfaq/116_0701_p...eter/index.html

[T04GTR]

micrometre is best, but ive always used plasti guage with out issue. you just have to be very careful with it. you get a feel for it after a while

[Guishnu]

I'll pull out the crank, clean, replace and re-check the measurements.

If the big end clearances are too big, can i get a few thou machined off the cap face to tighten them up? Same with the main bearing gurdle?

[Guishnu]

I'll pull out the crank, clean, replace and re-check the measurements.

If the big end clearances are too big, can i get a few thou machined off the cap face to tighten them up? Same with the main bearing gurdle?

Lol

Never mind - I know milling the caps isn't possible.

I’m even more retarded then usual (but it's always good to make 110% sure!)

Oil Clearances

Mains

OEM Standard Bearings 0.028mm ~ 0.046mm / 0.0011” ~ 0.0018” with a limit of 0.090mm/0.0035”

Big Ends

OEM Standard Bearings 0.020mm ~ 0.039mm / 0.0007” ~ 0.0015” with a limit of 0.090mm/0.0035”

My mains are running 0.046mm/0.0018” (aprox)

My big ends are running 0.050mm/0.0020” (aprox)

So I’m golden.

Few.

Edited February 25, 2010 by Guishnu

[Ziller]

Any comments. Machining your crank, Measuring up your bearings to your exact chosen spec's, after then, bolting on your sump, then bolting on the head with let's say with a multi layered steel shimmed head gasket. Any changers to your bearing measurement's after this process?

[T04GTR]

if its to loose you will have to get the crank ground to a undersize and get the same undersize bearings.

i think they go 10 and 20 thou under.

[Swiper the Fox]

if its to loose you will have to get the crank ground to a undersize and get the same undersize bearings.

i think they go 10 and 20 thou under.

they also come 1 thou under.

[zebra]

Thread revival!

Where in the bearing tunnel is the best spot to measure for clearance?

Should the caps be torqued up with out the crank inplace or...?

[GTR1993]

Thread revival!

Where in the bearing tunnel is the best spot to measure for clearance?

Should the caps be torqued up with out the crank inplace or...?

put in your bearings, then mains caps, girdle and bolts that you will use (torques down). measure each main tunnel. U can measure at different spots on each tunnel. at say 12 and 6, 2 and 8, 4 and 10 o'clock etc.then measure up each journal of the crank. If the clearances are too big then you can get the caps machined down and the block line bored again to a size that is more appropriate.

Edited May 19, 2010 by GTR1993