rod end play

D

Dirtslinger

Member
I have another question, I've got my bottom end together on my 8ba, I noticed that there's very little end play on the rod journal's, is there a number that I should be looking for? Possibly use a feel gauge to check?
 
No. Use feeler gauges of same size. You are using each side of journal to keep rod square.
 
BTW, having larger clearances (on the higher side of the spec Tony posted) is not a bad thing for any higher performance flathead. It helps in letting more oil out of the bearing (faster) and cooling it.
 
Dirtslinger said:
That makes sense. Im getting about .009 on mine, it will have to do.
Click to expand...



Sometimes a tight reading is caused by the fillet radius on the crankshaft being large. This causes the rod bearings to push towards the center of the rod journal. When that happens the connecting rod bearing edges that faces the crankshaft radius needs to be chamfered doing this now gives more clearance between the rods. Sometimes a large radius happens when the crank rod journal is ground undersize. And can also happen when your using an aftermarket crankshaft especially if its a specialty crankshaft made for higher performance out puts.
Ronnieroadter.
 
Ronnieroadster said:
Sometimes a tight reading is caused by the fillet radius on the crankshaft being large. This causes the rod bearings to push towards the center of the rod journal. When that happens the connecting rod bearing edges that faces the crankshaft radius needs to be chamfered doing this now gives more clearance between the rods. Sometimes a large radius happens when the crank rod journal is ground undersize. And can also happen when your using an aftermarket crankshaft especially if its a specialty crankshaft made for higher performance out puts.
Ronnieroadter.
Click to expand...

Great point from Ronnieroadster. I find this very common on the stroker cranks I have ground so now always check this as some bearings are way too tight at radius.
 
KiWinUS said:
Great point from Ronnieroadster. I find this very common on the stroker cranks I have ground so now always check this as some bearings are way too tight at radius.
Click to expand...

This is exactly what I just finished doing. Gotta make them floaters float.
 
It is important for a crankshaft to have a good fillet/radius in the corners of the journals - it sure helps in strength and to prevent cracks right in the corner of the journal. I've had to chamfer bearings on quite a few engines to account for the chamfer.

For some modern engines (SBC, BBC, etc.) you can order "narrow bearings" to deal with the issue (especially on the mains) - we don't have that option on standard/stock flathead bearings - they may need to be "fitted".

On the H-beam rods with Buick bearings, the bearings are narrow, so the typical place you can get into trouble is with the big-end rod bore itself. You'll notice that in many rod designs, they will have a big chamfer on the outside - to NOT rub on the crankshaft journal fillet/chamfer radius.

Newbie engine builders sometimes don't pay attention to the rods and which side has the clearance/chamfer for the journal fillet. They install the rods with the fillet to the inside, then the rod drags on the crank and really bad things happen . . . like a rod thrown through the side of the block. ;)
 
Last edited:
After further consideration, Im thinking I may need to chamfer these rod bearings. It still seems quite tight in there. The other option would be a different set of rod bearings that are more narrow?
 
Have you tried removing the bearing shell from a rod and cap and checking side clearance with it bare? May not be the bearings touching at all.
 
Dirtslinger said:
After further consideration, Im thinking I may need to chamfer these rod bearings. It still seems quite tight in there. The other option would be a different set of rod bearings that are more narrow?
Click to expand...

What brand connecting rods are you using are they Ford 8BA rods? What crankshaft is it Ford , Scat or?
Ronnieroadster
 
Using 8ba rods with oem merc crank. I put the arp rod nuts on and again checked side play and I’m satisfied with it. I’m going to run it, next I need to make an engine run stand. I’ll be asking for help with that.
 
I always have to chamfer all of the bearings to clear the radius's in the cranks we use.
We run .030 total side clearance and the rods have piston oiler grooves in the side face.
Running tight side clearance and tight chamfer clearance is guaranteeing a spun bearing.
 
You must log in or register to reply here.
Back
Top