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Discussion Starter #1
Running down the mains for bearing replacement on a 69 351w and I am getting some differences. The block was supposedly line bored and set with a .003 bearing clearance with standard bearing. My engine builder gave me a spec sheet with all the clearances when he finished the engine 3 years ago.

I bought two sets of the same bearings. After checking I am getting some differences that have me worried and I am not sure on what to do.


I just had the crank re polished and all the journals on the crank measure 2.9993 to 2.9994.

The block with the bearings installed is a different story.

Front main .0028 clear
2nd main .0028
thrust .0033
4th .0025
5th .0023

I changed bearings in the back two caps with the other brand new bearing set just to be sure it was not a difference in the bearings and it was not.

So is safe to assume that the actual block is small in diameter in the back two bearings. Should it be aligned honed again to open that diameter up again. I have yet to check the main bore diameter with out bearings but will do so.

Thanks in advance
 

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Looks like another bad line hone job/ or you have a tuning problem that is elongating your main caps. Original sheet says .0030- +/- .0000? /not real numbers
 

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Metal moves and measuring instruments change. Did you check your micrometer with a standard at the correct temperature? Did your machinist? How are you measuring?
 

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I'm I correct to assume you are freshening up the engine after running it for 3 years?
 

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Discussion Starter #6
Metal moves and measuring instruments change. Did you check your micrometer with a standard at the correct temperature? Did your machinist? How are you measuring?
.


I have been a machinist for 16 years, just not a automotive style.

Mics checked against a starrett gauge block, with the federal dial bore set to same gauge block. All gauges normalized to temp. I trust my measurements but I am wondering now exactly what my engine builder put down.

Billyman

Yes, this is just a freshen up
 

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Running down the mains for bearing replacement on a 69 351w and I am getting some differences. The block was supposedly line bored and set with a .003 bearing clearance with standard bearing. My engine builder gave me a spec sheet with all the clearances when he finished the engine 3 years ago.

I bought two sets of the same bearings. After checking I am getting some differences that have me worried and I am not sure on what to do.


I just had the crank re polished and all the journals on the crank measure 2.9993 to 2.9994.

The block with the bearings installed is a different story.

Front main .0028 clear
2nd main .0028
thrust .0033
4th .0025
5th .0023

I changed bearings in the back two caps with the other brand new bearing set just to be sure it was not a difference in the bearings and it was not.

So is safe to assume that the actual block is small in diameter in the back two bearings. Should it be aligned honed again to open that diameter up again. I have yet to check the main bore diameter with out bearings but will do so.

Thanks in advance

I would check the main bores in the block without a bearing and see if the differences are in the bearing shell first and check for taper. Don't just measure middle of the housing bore, do inner and outer edge. I have seen differences in crank journals as well. It can't hurt to re-line hone the block this time around. I like the clearances from 1-3, 4 is ok and 5 is on the tight side. I tend to open the clearance on the thrust side as well, with modifications I do to the thrust surface of the bearing. Let us know.
 

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My block had a similar deal. It was small on the ends and large in the middle.

I think I had #1 .003, #2 .0035, #3 .004 , #4 .0035, #5 .003. I checked with mics first and then plasti gauge, any they were right on. I ended up half shelling #1 and #5.

I originally ask my machine shop to check if the block needed an align hone (this is a brand new Dart Big M), they said it was good to go.

I also checked it with the #1 and #5 bearings like Reher Morrison says you can do to check the align bore and it was good.

The machine shop said it is not uncommon to see this.

Sounds like we are in the same boat. I miced all the mains without bearings and they were all on Dart's spec.
 

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My opinion:

It's not what you want to see, it's not what was documented in the beginning. As an engine builder and automotive machinist myself, I smell a rat............however, it's been running like that for 3 years and I assume without issue?

I wouldn't worry with having the block align honed again just to get those bearing clearances like you want them. Pick up a set of +.001 bearings but only use half shells on the 4 and 5 journals. Use the half shells in the block, not the caps in this case. The extra clearance on the thrust bearing isn't of concern. I typically like a little more clearance on the thrust to help lubricate the thrust sides of the bearing too.
 

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My block had a similar deal. It was small on the ends and large in the middle.

I think I had #1 .003, #2 .0035, #3 .004 , #4 .0035, #5 .003. I checked with mics first and then plasti gauge, any they were right on. I ended up half shelling #1 and #5.

I originally ask my machine shop to check if the block needed an align hone (this is a brand new Dart Big M), they said it was good to go.

I also checked it with the #1 and #5 bearings like Reher Morrison says you can do to check the align bore and it was good.

The machine shop said it is not uncommon to see this.

Sounds like we are in the same boat. I miced all the mains without bearings and they were all on Dart's spec.

I would have thought you would have half shelled 2,3, and 4 tighter. .004" is way too much clearance. .0025"-.003" is perfect depending on block and applicatio and I go about .0005" bigger in the thrust bearing. Nothing wrong with half shelling to fine tune the clearance, but you need to make sure the housing bores are straight.
 

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I have no idea why people adjust bearing clerance with the line bore. work the crank or the bearing. Bearing Crush is your friend.
 

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I have no idea why people adjust bearing clerance with the line bore. work the crank or the bearing. Bearing Crush is your friend.
I agree but would only advise to those with proper checking equipment. Too much crush is no ones friend when the bearing distorts. Most people don't have the equipment to properly check for distortion. Hell, most don't know how to check to see how much crush they actually to begin with. Know what I mean?
 

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I would have thought you would have half shelled 2,3, and 4 tighter. .004" is way too much clearance. .0025"-.003" is perfect depending on block and applicatio and I go about .0005" bigger in the thrust bearing. Nothing wrong with half shelling to fine tune the clearance, but you need to make sure the housing bores are straight.
Maybe for a small block, but not on a 598 BBC. You really want around .0035 and some guys go .004 on mains.

I will see how the pil pressure is, but I do not think the #3 with .004 is going to cause a problem.
 

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I agree but would only advise to those with proper checking equipment. Too much crush is no ones friend when the bearing distorts. Most people don't have the equipment to properly check for distortion. Hell, most don't know how to check to see how much crush they actually to begin with. Know what I mean?
Yep.
 

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Maybe for a small block, but not on a 598 BBC. You really want around .0035 and some guys go .004 on mains.

I will see how the pil pressure is, but I do not think the #3 with .004 is going to cause a problem.

It doesn't matter what it is. My drag high compression race 388 Dart block bracket engine gets the same clearance as my 707's with 2 stages. Clearance is clearance and there is not a wide variety of clearances to choose from. It is either too tight, good or too loose and in my experience is not cubic inch specific. There are other variables I look at when deciding on final clearance for mains and rods, but cubci inch isn't one of them. That is not only coming from experience, but it is alos what the engine tells me upon freshen ups with ALL different style,type, and make engines from 400-2000+ hp. However, when I have seen guys run .0035"-.004"+, the bearings do not look happy upon teardown. Never had a bearing failure due to the .0025"-.003" clearances I run. Ofcourse, it is your engine and you can build it however you like but don't say that they NEED .0035"-.004" because that is completely false. Cheers.
 

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I have no idea why people adjust bearing clerance with the line bore. work the crank or the bearing. Bearing Crush is your friend.
I agree. No need to constantly line hone an engine because the housing bores are slightly off. Like I said before, straightness is more important. Only time I will line hone if they ARE straight is if there is way too much taper from front to back of same bore. But different sizes, for the most part shouldn't be a reason to do it. There are some other tricks you can do other than half shelling it to fine tune the clearance. I also recommend 3/4 grooved bearings as the bottom shell sometimes acts like a scraper on the journal. The tail helps for a smoother transition for the oil to get in the bottom half od the shell.
 

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It doesn't matter what it is. My drag high compression race 388 Dart block bracket engine gets the same clearance as my 707's with 2 stages. Clearance is clearance and there is not a wide variety of clearances to choose from. It is either too tight, good or too loose and in my experience is not cubic inch specific. There are other variables I look at when deciding on final clearance for mains and rods, but cubci inch isn't one of them. That is not only coming from experience, but it is alos what the engine tells me upon freshen ups with ALL different style,type, and make engines from 400-2000+ hp. However, when I have seen guys run .0035"-.004"+, the bearings do not look happy upon teardown. Never had a bearing failure due to the .0025"-.003" clearances I run. Ofcourse, it is your engine and you can build it however you like but don't say that they NEED .0035"-.004" because that is completely false. Cheers.
I guess what I was trying to get across with the cubic inch is that when you run a large cube engine, generally you have more rotating mass, longe stroke and more HP. Those does effect what clearances you need to run.

You can do what every you want. Both Callies and Reher Morris ion said .003 is too tight for this combo. Along with several others on this site.

If your clearances work, then that's all you need.
 

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Ah, the old clearance debate!!!!

This one should get good!
 

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Discussion Starter #20
Easy boys, I dont want any pissing match. Just trying to get some informative information to try to make this right atleast in my mind anyway. I figure that I did run this thing for 3 years this way but now that I know the way it is I wont let my mind rest till I atleast know its right.

Thanks for the info so far.
 
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