cam bearing clearance

[brra1961]

Starting to assembly my D4TE block, using durabond FP-33 bearings , I first put them in with the hole facing up noticed my mistake then removed them and put the same bearings back in with the hole facing down. the bearings went in and out smooth and straight and looked fine so I reused them , I measured clearance with a bore mic. at .003 - .0035 The cam went in easily from the front thru the first 3 journals , the 4th got a little tighter but still turned easily and the last journal had to give it  a little tap. I could rotate the cam with the bolt and the dowel by hand but it took some effort. I removed cam and installed from the rear as a test, same thing smooth thru the first 3  and binds up a little on the last one. I've searched old posts here and read that its fairly common to have cam journal misalignment and about shaving the bearings with a knife and scotchbrite and also using a hammer and a drift  on the cam next to the journal , I decided to use the 1st method. I rotated the cam for a while then removed and noticed wear marks on 3 different bearings ,I shaved a little off each one and cleaned them up with the scotchbrite then installed cam and  was better, I had to repeat this procedure one more time to get the cam to turn easily using the bolt and dowel, then checked clearance and there between .005-.007 .  So my questions are ,  is .007 clearance acceptable ?    and is it acceptable to reuse cam bearings that were previously installed then removed ?     This is a 447 with a .620 lift 231 @ 50  hyd. roller .  any advice will be appreciated

[blykins]

You can reuse bearings like that.  If you pop them out 2-3 times, then I would put a drop of green Loctite on them before you drive them in the last time. 

How are you measuring the clearance?  With a micrometer and bore gauge? 

For future reference, if you do another FE, grab an old junk factory cam and cut some cutting grooves in the journals.  It will save you a lot of time on fitment.  None of the aftermarket FE blocks will give you fits on cam bearing installs, but a lot of the factory blocks are just badly out of alignment. 

[pbf777]

     Generally in the current aftermarket/performance marketplace of componentry the realized as measured camshaft to bearing clearances often will fall somewhere in excess of say............003".  This is as between that of the targeted value by the bearing suppliers today is in the range of .003" +/-, which is somewhat greater than that of decades ago and was intentionally made greater with the introduction of the "aluminum" bearings.  We were involved in testing with Clevite in the early eighties as they experimented with different materials in an attempt to alleviate the problems of unacceptable fatigue failure rates becoming evident in the "babbitted" material bearing overlays, finally adopting the aluminum alloy, though quickly realized (as we demonstrated to them!) that the greater expansion rate presented unique problems not experienced in the other materials (there were a few), with the final decision that the solution adopted would be to just increase the clearances over that previously established.  But this clearance dimension sum was based on the nominal values of the standard journal dimensions, but the performance camshaft industry often chooses to deliver journals sizes on "low" to even undersized dimensions, this to alleviate complaints of cams not turning in blocks (obviously incurred do to a number of possible reasons) but this helped in silencing the telephones (before internet!), so now we're often in excess of .003", coming close to .005" sometimes (again, a number of participants involved even beyond that being mentioned here), but .007"(?),...................... that's gettin' kinda big!   

     Scott.

[brra1961]

Thanks Brent
Yes, I'm using mic. and bore gauge , I've read your posts about the cam cutter cam, do you measure clearance after that procedure ? what kind of numbers are you seeing ?
I just assumed cam bearing clearance would be more critical . At what point would you bore the tunnel and use the largest bearing on all journals ?

[blykins]

I usually see .003-.005" normally. 

I don't think .007" will hurt you, especially just on one journal. 

Somebody, who shall remain nameless, but his initials are Brent Lykins once put a 390 together with a .010"/.010" crank and standard main bearings.  It had like .012" main bearing clearance.  Oil pressure at idle was good, it had 70 psi at full pull on the dyno, but after a pull, it would go to single digits.  That's how I knew something was wrong.  Tried a different pump on the dyno, same deal.  Tried different viscosity oil, same deal. 

Took it home, pulled the pan, hooked up a special pump with a hose fitting and then primed the pump while I watched from underneath.  Looked like Niagara Falls. 

On a cam bearing, I'd rather have more than not enough.  I'm real particular on my engines with very high spring loads about the cam bearing clearance. 

[preaction]

How long ago was that Brent ?

[blykins]

Several years.  Why do you ask?

[preaction]

It gave me a mental picture of the pics you shared recently of your first engine build you looked pretty young 

[blykins]

It gave me a mental picture of the pics you shared recently of your first engine build you looked pretty young 

Yeah, I still make mistakes when I'm old.  That's why I'm as bald as a cue ball.

That fiasco opened my eyes up a little bit.  When you can pull an engine on the dyno to 5500 with .012" (twelve!!!) main bearing clearance, all these guys screaming on the internet, "DON'T NICK A CAM BEARING YOU WILL LOSE ALL YOUR OIL PRESSURE" get a chuckle from me. 

That's why I said an extra .002" cam bearing clearance on one journal for the OP won't hurt anything.

I pulled all the caps off of that engine after I found the leak.  All the crank journals looked perfect, bearings looked perfect, etc.  I pulled the crank out, swapped in new bearings, bore gauged the clearances, put it back together, and dyno'd it again. 

It had been a perfect storm for mistakes.  Either someone had mispackaged a set of bearings, or I had put a set of standard bearings in a .010" box at some point.  In addition, my Mitutoyo bore gauge only goes to .005".  So a multiple of 5 is kinda undetectable. 

Things shape your experience and "rules" over time.  This is one of the reasons why I tell everyone to spin the pump on the stand, listen for odd noises, and know that certain pumps will pretty much always make the same oil pressure on the gauge with the same drill motor spinning it.  Looking back at it, it had "enough" on the gauge, but it didn't have what it should have had.

[My427stang]

I wouldn’t have believed it if I hadn’t seen the video of the geyser

No engine builder gets out alive without sone good stories!

[pbf777]

     Remember, the concerns are not all just about oil clearance sums and the resultant oil bleed off rates; and in example particularly in the instances of possible inconsistent shaft journal landing alignment relationships possibly resulting in potential failure to provide adequate support in the length of the shaft, or causing specific loading sums on say the two adjacent journals perhaps that which may displace the oil film separation function there.   

     And to add in thought:  In the old days, with the  thicker babbitt bearing overlays one could get away with greater alignment issues, as this softer material provided greater "conformability" function in service than the thinner, harder aluminum material examples popular today, but yes, also often failed to provide the necessary load carrying capabilities and fatigue resistance, hence it's obsolescence in more modern times.   

     Scott.

[mike7570]

Took it home, pulled the pan, hooked up a special pump with a hose fitting and then primed the pump while I watched from underneath.  Looked like Niagara Falls. 

Mine was Niagara Falls on steroids, lol. I was rebuilding a 427 tunnel port and I took it to a shop in So Cal that was well know for Chevy Stk SS race cars. I figured they would do a good job on the bore and hone for a 4.250 BBC diameter. I got the engine back and it sure looked good and I needed to get it back in the car and running for the Winter Nationals. I finished it up only a few days before the race and fired it up and set the timing. It had about 50lbs on a high idle and would sweep up with a quick rev. I didn’t run it long enough to build any heat and loaded it on the trailer. At Pomona after setting up my pit space I started the car and headed over to tech. About a few minutes into the trip to tech the oil pressure started falling and went to almost zero, I shut it off and towed it back to the pits. I fired it one more time and the oil came up then immediately dropped to zero. I took it home and started checking and wasn’t finding any reason to lose oil pressure. With the pan down and a pickup in oil I primed the motor, Niagara Falls was an understatement. It turns out the Chevy guys put the block by-pass spring in backwards!