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Modifying bearings for extra clearance?

CSVT#49

CSVT#49

Addicted CEG'er
Joined
May 28, 2004
Messages
6,771
Location
Andover, MN
Alright so I've been struggling with assemblying my engine because I want the perfect bearing clearance for my build. Right now Clevite and ACL do not currently offer a thinner bearing to provide an extra 0.001" of clearance (per catalogs). I've done researching on-line and talked with a number of machine shops and received various opinions. Here are the things I've found.

1. Polish crank
Not possible to polish a crank to remove 0.001". Doing so will leave an uneven journal surface, only way to do it right is to machine it down 0.010" and reharden the crank, which I am not allowing as an option at this time.
2. Line hone block/rods
Same boat as above for line honing
3. Use thinner bearings
Not available for this application per available catalogs.

So what I have found people doing on the web is taking Scotch-Brite pads/sandpaper and taking material off of the bearings. I've seen this mentioned two different ways, one making a lot more sense then the other. Taking material off of the bearing wear surface. On most bearings there is a wear coating. Removing this wear coating can provide an extra 0.001" of bearing clearance, but will reduce the life of the bearing. I'm not a fan of this method. The second method was to use the Scotch-Brite pad to remove material off of the back side of the bearing surface. This makes more sense to me as this surface is not going to come in contact with the crank journals. Also this method I would imagine would replicate what one could buy, if available, for the thinner bearings that are offered by Clevite (X-series) and ACL. Only issue with this is that it will be very, very time consuming. I would need to remove an equal amount on all sides to keep a true profile and to ensure even clearance across the bearing surface.

Any thoughts/comments on this guys? I'm thinking this is my best option to obtain the bearing clearances that I want and that were recommended. I look at it this way... if I screw up the bearings, I can buy new ones. If I don't do this I could have a spun rod/main bearing on my hands from to tight of a clearance.

I'm still going to call Clevite and ACL Monday just to make absolutely certain they do not offer a thinner bearing.
 
alley said:
I would just leave it. The break-in "might" give you the 0.001" your looking for.
Click to expand...

Yea... might is not good enough for me. One guy I talked with (name was Guy) at DG Motors in MN (shop that machined my brother's block for his VTEC/LS hybrid build) told me about a NSX that he did were the guy said, "nope, those clearances are fine. They are with in the OEM spec", and then when they broke it in on the dyno it spun two rod bearings. The guy has also built a number of Ford engines, no Duratec motors, but he still knows his stuff. I'm not willing risk the kind of money I have in this build on the chance that I "might" get an additional 0.001" clearance :shrug:. He was also the guy that recommended talking with ACL as he has run into this problem with a number of Subaru engine builds where Clevite bearings had to tight of a clearance and found that the ACL bearings provide a larger clearance enough to put it into an acceptable range. However when I checked the ACL bearing catalogs they were still showing the same bearing thicknesses as Clevite, 0.0985"(mains) and 0.0591" (rods).

The only other thing I am wondering about is whether or not the gasket sealer and anaerobic sealer will give me any additional clearance on the main bearings since I am not assembling the lower half of the block with these when checking the clearances. I doubt it, but just another thing to throw out there. Even so I would still have to worry about the rod bearings.
 
If you are using 5 W 20 synth. then you will be fine. If you want to run 15w40 or 20w50 then you will need more clearence. If it is in spec then it won't go boom. I hear stories all the time in my sport about engine builders *claiming* they spun a rod because of it. Turns out they assembled the engine improperly. If the .001 tight caused the problem then all the rod bearings would show signs of spinning, not just one.

What was the clearence when you took the old motor apart?

I would ask Terry's opinion on www.fordcontour.org site since he was a powertrain engineer at Ford. He may have insight on this subject.
 
crewchiefpro said:
If you are using 5 W 20 synth. then you will be fine. If you want to run 15w40 or 20w50 then you will need more clearence. If it is in spec then it won't go boom. I hear stories all the time in my sport about engine builders *claiming* they spun a rod because of it. Turns out they assembled the engine improperly. If the .001 tight caused the problem then all the rod bearings would show signs of spinning, not just one.

What was the clearence when you took the old motor apart?

I would ask Terry's opinion on www.fordcontour.org site since he was a powertrain engineer at Ford. He may have insight on this subject.
Click to expand...


It never occurred to me to check the bearing clearances on the old parts.
 
No real world experience here, but trying to evenly remove .001 with scotch brite doesnt sound precise enough.

.02
 
SHOgoFast said:
No real world experience here, but trying to evenly remove .001 with scotch brite doesnt sound precise enough.

.02
Click to expand...

yea it's actually half that... I need to be able to remove 0.0005" from each bearing half on the rods. However I do have to remove 0.001" per half on the mains. Instructions say to mic each half with every pass to ensure proper removal.

All that said I am still working with the bearing suppliers to see if I can possibly obtain some custom thinner bearings.

Part of me is just wanting to use what I have, but I am not willing to deal with the consequences if it were to turn out badly.
 
mike, anaerobic DOES make a skin that will change clearances, but that tolerance is not considered in an engine build, because it isnt' a constant. it will however give you a little more clearance. it scares me to think your going to open up the tolerances, but i did just realize you will be running some heavy oil! good luck :)
 
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