Rod Side Clearance Issue?

[swflastang05]

I just finished assembling my short block and while checking the number 3&7 rods side clearance I ran into a weird problem. Using the two feeler gauges method I have .010 clearance for about 2/3 of crank rotation, however they seem to pinch down while the crank is in a certain position. While the crank is in the tightest location the side clearance drops down to .006, which is technically still within OEM spec but I was really wanting .010 - .011. Is this common? There seems to be the same issue with the 4&8 pair but they drop down to .008 during the tight areas and are .011 otherwise. The other pairs don't seem to have this issue. Please tell me I don't have to tear the motor down again and bring those rods back to the machine shop!

 

[BruceH]

Did you check crank shaft runout prior to putting the main caps on?

 

[swflastang05]

yes it was okay @ .007. I've been messing around with it more and found the 1&5 pair does it too just not as much, maybe closes up .001 or .002 as the crank turns.

I just re-read your question and see you mentioned PRIOR to installing the main caps, that I did not do. I checked end play after installing the mains and torquing them to spec. Also just remembered Manley spec for my H beam rods is .010-.020. I see where this is heading!

 

[BruceH]

I just re-read your question and see you mentioned PRIOR to installing the main caps, that I did not do. I checked end play after installing the mains and torquing them to spec.

Not end play. Runout. Runout is the amount of variation as the crank turns. Basically it's a measurement of straightness. IIRC the stock spec allows for .001"

 

[swflastang05]

No I did not check for that then.

 

[BruceH]

A guess would be that the crank is bent a little at the #4 main. Runout is something a machine shop checks. Did they mention anything about straightening it?

If that's the case I'm not sure what it would do. Maybe beat the bearings out a little? Maybe tighten up the #4 clearance at times?

Keep in mind I'm not a mechanic and just making a guess. It could and probably is something completely different. Hopefully someone with more engine experience will chime in.

 

[swflastang05]

I talked to my machinist this morning and he said its highly unlikely the crank is bent, but there's probably a slight variance in the journal diameter of that pair from side to side. He suggested I should bring the rods back to him to take some material off the sides until the tightest clearance area is at .010-.011 then the widest area will be .014-.015 which is still well within Manley spec. Makes sense to me but I'm no professional... So much for assembling the rest of the motor this weekend!

 

[BruceH]

The Ford max spec is .016" iirc. Were the rods used? Any Manley rod I've used has been spot on with the machine work.

When he says "highly unlikely" does that mean he didn't check runout in the block?

 

[swflastang05]

I figured it out! After I removed the back four rods (planning to bring to the machine shop Monday morning) I closely inspected them and took several measurements with a micrometer low and behold I found three of those four rods had burrs on the sides!!!!! I know I didn't do that so it must have happened either at the machine shop or balance shop in any case I removed the burrs, reassembled, and re-measured and sure enough they're all spot on now! Needless to say I was relieved and of course continued on with my motor assembly. Got everything ready to degree the cams in tomorrow. Started tonight but when I couldn't even get TDC I decided it was a good time to quit for the day!

 

[gregsdart]

Glad you found it. I have seen the side clearance issue you had also come from rods not being perfectly aligned when tightened down, IE the caps would be offset a touch. The way to avoid this is to use feeler gauges (two, one on each side) between the rods to hold everything in place while torquing. Make sure the gauges are between both the rod body and caps on both rods.The feeler gauges can be removed as soon as there is a little torque on the bolts to hold them in alignment.