Loose main bearing clearence

sid

sid

Greenie N00B Member
Hey everyone,

I'm currently in the process of building my mzr disi for my speed 6. Ive been measuring my clearances and everything was a ok for my Manley rods (0.002" bearing clearance), which is at the bottom spec of what Manley recommends and the top of factory spec so I am assuming this is alright.
My concern is my main bearing clearances which turn out to be about 0.0028"-0.003" which is double the maximum standard clearance from the shop manual. Thing is the maximum allowed clearance is said to be 0.0039" so does this mean I am within spec? If i do run these clearances on the mains, should I expect to run with thicker oil?

Im planning on using this as my summer DD. Currently have a bnr s3, supertech pistons and Manley H beams. Im not planning on doing any fueling mods to this yet but plan on doing it in the future (maybe next year). Any tips/help would be appreciated as the last thing I want to do is take this thing apart again because I didn't make the right call.
 
The stated maximum allowance would be for a used motor. You are going to want to be in the recommended range on a fresh build
 
Ok thanks that make sense. Im just a little confused as to why my clearances are so far from standard. I might be completely wrong with these assumptions but here it goes. My main journals mic'ed at 2.0466" and the right crank journal size for standard bearings is said to be 2.0465 - 2.0472. If i wanted to be in spec my crank would of needed to be at least 0.0015" larger for the clearence to be smaller but then the journals would be out of spec according to the manual (2.0480"). So how is my bore so large? I wouldn't expect the main bore to wear out so maybe I didn't torque my girdle on right? I reused my main bolts from my engine so is it possible i need to torque the bolts down a little more since they are already stretched? Thanks for the help

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Any idea what could be causing the clearance to be so wide? Ill check to see if the used bolts stretched at all from comparing with the new ones. I just dont see how my clearances are so wide if my crank specs out ... Unless the bore the crankshaft sits in is too wide from manufacturing or some machine work done to it i dont know of ... Or the bearings are too thin.
 
So, in order to regain my sanity, i checked my clearances with plastiguage. 0.002 clearances almost on the dot (according to my eyes). Either i didn't measure my clearances right or didn't torque my mains right when trying to measure the first time.
 
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Plastigauge is less accurate but is more guaranteed if you don't use the tools correctly.

I ran into the same trouble as you, unfortunately there is nothing I could do about it as there were no bearings available to compensate for that and this engine showed no signs of damage in the bottom end... I ended up going slightly over-spec for ARP main studs to reduce the clearance. I run 5W40 and have had the engine running for the past 30k km without bearing issues.

Hope that helps.
 
I know some companies make undersized bearings. I know Kings does. Could get some of those and give them a shot. I believe you can buy them on Edge Autosport as well
 
RyanMunsell said:
I know some companies make undersized bearings. I know Kings does. Could get some of those and give them a shot. I believe you can buy them on Edge Autosport as well
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Make sure you confirm they can get them. When I tried to buy them, there was a 4-6 month lead time before they can get them in stock. Even though they list them as "Available" on their website.
 
Bumping an old thread for knowledge and information.

Bearing clearance is extremely subjective and widely debated what is acceptable even with a manual and provided clearance range. Many factors play into this. Type of driving, racing, N/A or boosted, RPM, rod material etc.

If you took my blueprint sheet and looked at it without knowing what the engine was intended for you'd say it's wrong and no way it'll work or last.

Main clearance on my motor is .0022-.0024 and rods are .0019-.0021

This is just food for thought and always remember the old saying

"If its loose only you will know, if it's tight everyone will know"
 
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