Uneven main clearances after line hone – could the machine shop have messed up?

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Barracuda_v8

Barracuda_v8

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Hi,

I had my 360 line-honed last week and installed new Clevite H-series main bearings.
When checking with Plastigauge, I got these clearances:
  • Main #5 (rear): 0.0010"
  • #4: 0.0017"
  • #3: 0.0020"
  • #2: 0.0015"
  • #1: 0.0015"
The crank journals all measure 2.810", and everything was torqued in the correct sequence using the same specs the machine shop used during honing.

The strange part is that #5 is considerably tighter, while the middle mains are looser. That doesn’t line up with what I’d expect from a proper line hone.
My opinion is that all of them are on the tight side — especially #5.

I know Plastigauge isn’t 100% accurate, and I’ll verify everything with a dial bore gauge when I get home tonight, but the pattern still seems odd enough to question.

Question:
Could the machine shop have made a mistake, or is there something else I should be checking?

Also, what main bearing clearance should I be targeting?
It’s a 408 making around 550 hp. I’m thinking 0.0020"–0.0030", but I’d like to hear what others are running.

Any input is appreciated.
 
if possible i'd be swapping bearings around. no idea which is your thrust and if the rear one has the same bearing as the rest as i don't know a v8 but i have moved both or 1 part about to get satisfaction in the past

i run a 7 main bearing crank in a 300bhp 300ftlb six with 2.5 inch mains

As standard from the factory the mains were supposed to be 0.0005 -0.0015 with a note to say replace bearings if clearance gets to 0.0025 as it will result in low oil pressure that will impact the hydraulic lifters.

i have no options on high volume oil pumps, i have to make do with a 50 year old one with a new impeller so mine was built to 0.0015 and carefully run in.

yours are 2.8 inch journals so the clearance as standard would have been bigger than mine.
for a race build you would set the clearance to the workshop manual worn out spec...

mine: if built for pure race work. should have been set up in the 0.002 to 0.0025 range but 90% of my driving is on the street. so i went for standard clearances 0.0015 and careful 500 mile run in before taking it down the track... break in oil changed followed by 500 miles on break in oil for running it in...
been pretty good for 10 + years

think on a 360 standard is 0.0015 to 0.0028

so the only one you truly have a problem with is the no.5 and by the time you put the seal in and a smear of silicone on the faces of the cap you may well be OK...try it...

bodge it options...or make it work in a manner that will appall/dismay some people.

1) lightly rub down the back of the bearing with 800 grit wet n dry and a lot of wd 40

2) put a piece of 1 thou shim stock under each side of the rear most cap.. drill it when clamped between 2 pieces of ply then cut your shim using a box cutter and a steel rule as a guide make sure the shim covers the full mounting face.

3) wind 400 then 800 then 1200 or finer wet and dry around the crank journal. start with 400 then 800 then really fine, douse with diesel and then use a leather strap wound twice or 3 times round the journal as a pull to polish the journal and hence slowly reduce the journal size.

  • 1 and 3 take quite a long time....
  • keep in mind that both 1 and 2 reduce the crush on the bearing and if you go too far it could spin.
  • standard crush pushes the sides out slightly, to produce a friction based side force locking the bearing into the cap and saddle... you can only spot it really with a nice bore gauge.

Dave
 
Also, I'd start over with cleaning, torque to spec (not whatever the shop used) and a bore check without bearings to see if it needs to go back.
 
oh yeah
and i'm not saying you are...
if it was align bored using the original bolts and you are now replacing them with studs you will see variation.. work needs to be done, much like with con rods, using the hardware you intend to use in the build.
 
.01 would be 10 thousands. You need to go .001 1 thousand more clearance. Your to tight. The machine shop probably honed the block with a bar with stones. We do not line hone. Only line bore. .

When ever you line hone you are taking material out of the block and cap. this moves the crank closer to the cam. If you do that on a gear drive engine such as big diesels the lash on the gears will be tight.

We set up the line boring bar to cut the material out of the cap. a boring bar has cutters and are precise. a hone has stones and they wear on the ends and you usually have to turn the block around to try and get an even hone. If a shop says line hone run away. All race blocks are line bored from new and should never be honed.. Never cut the saddles only the caps and you cannot do that with a hone. Honing is to size cylinder bores.

You can't take it back to that shop. You'll end up with junk. Be happy you can fix their screw up with over size bearings. One more hone job by them you'll need a special shorter timing chain. I think the shortest one is .010 under. If anything take it to someone with a new line bore machine. We cand do up to a 5 foot block.. Line bore not 1930's line hone. That was OK for the old flat heads with three mains.

100_0007 (5).JPG


100_0008 (2).JPG
 
Honestly I can sympathize with you having an American car in the land of Saabs and Volvos. While those clearances are too tight and somewhat all over the place, alot is going to depend on the type of oil you are going to run, conventional or synthetic or blend and the weight.

All of the responsences you have got here are of good merit.

That being said, first thing I would do is call the shop that did the work and tell them of your problems. Depending on what they tell you, you have a decision to make, continue to work with them. For any further work to correct this with whomever, I suggest supplying the shop with the crank, bearings and all hardware that will be used so it can be machined to fit. Be specific with the type of oil you will use.

I would never tell anybody not to build their engines or not to check others work done for you, but I would never expect someone to work on a engine block without supplying the pertinent mating parts and getting everything correct.
 
You need a bore gauge and a micrometer.

Set the bore gauge to the middle of the housing bore dimension.

Measure the bores and you will quickly know if the machine shop jacked up the main line.

Chances are, the bearings are junk ****.

Unless you are hell bent on using a 20w50 oil, or if you can’t get anything else any more than .0025 on the mains is just pissing oil out of the bearings.
 

Barracuda_v8 said:
Hi,

I had my 360 line-honed last week and installed new Clevite H-series main bearings.
When checking with Plastigauge, I got these clearances:
  • Main #5 (rear): 0.0010"
  • #4: 0.0017"
  • #3: 0.0020"
  • #2: 0.0015"
  • #1: 0.0015"
The crank journals all measure 2.810", and everything was torqued in the correct sequence using the same specs the machine shop used during honing.

The strange part is that #5 is considerably tighter, while the middle mains are looser. That doesn’t line up with what I’d expect from a proper line hone.
My opinion is that all of them are on the tight side — especially #5.

I know Plastigauge isn’t 100% accurate, and I’ll verify everything with a dial bore gauge when I get home tonight, but the pattern still seems odd enough to question.

Question:
Could the machine shop have made a mistake, or is there something else I should be checking?

Also, what main bearing clearance should I be targeting?
It’s a 408 making around 550 hp. I’m thinking 0.0020"–0.0030", but I’d like to hear what others are running.

Any input is appreciated.
Click to expand...
A hair more like high .019 or .0022 would be great in a full groove bearing with mostly street miles.
The rear main is too tight.
The no.1 main believe it or not is fine at .0015.. and i prefer it between .0015-.002 while the others i like @.0022-.0025, without oil mods that is.

It should have been line honed with the studs in it and they need to open up that rear more regardless.
 
Last edited:
MOPAROFFICIAL said:
A hair more like high .019 or .0022 would be great in a full groove bearing with mostly street miles.
The rear main is too tight.
The no.1 main believe it of not.. is fine at .0015.. and i prefer it between .0015-.002 while the others i like @.0022-.0025, without oil mods that is.

It should have been line honed with the studs in it and they need to open up that rear more regardless.
Click to expand...
It was linehoned with the studs of course.
 
This is why I had the machine shop fit the crank for me after they did a line bore/hone job. They check fitment and clearances, then do whatever is necessary to get things within spec because they have the resources to get it done. This saves me from wasting time with BS trying to figure out what to do with the limited resources I have.
 
Last edited:
Again if they don't have a line bore machine don't take it back. They are taking material out of the block saddles with a hone. The more they hone the closer the crank gets to the cam. Find a shop that can line bore it true taking the material out of the cap. Hope they didn't go to far on the block saddle already.
 
Oldmanmopar said:
Again if they don't have a line bore machine don't take it back. They are taking material out of the block saddles with a hone. The more they hone the closer the crank gets to the cam. Find a shop that can line bore it true taking the material out of the cap. Hope they didn't go to far on the block saddle already.
Click to expand...
I don't know if this is true but I looked this up on several areas and they said that align hone removes a small amount of metal from both the main saddles and the cap, like .002".
 
Dan the man said:
I don't know if this is true but I looked this up on several areas and they said that align hone removes a small amount of metal from both the main saddles and the cap, like .002".
Click to expand...
That is if you take the material out of both. With cutters you can put the block where you want and cut just the caps. With a hone the stones need to cut the inner diameter same top and bottom, and as the stone wears the diameter gets smaller. cutters cut the surface true all the way through . Each cutter can be adjusted separately. Stones lose surface as they wear going through..
 
Good lord, there is NOTHING wrong with line honing a block, it's done EVERY DAMN DAY, by the best machine shops in the states. Maybe certain shops, cant do it, like the one claiming this nonsense, but trust me, it is NO issue when done correctly.
 
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