[scott70]

They’ve got the crank and pistons in my 70 455 for my gto. I asked what the bearing clearances came in at and they said .0029 mains and .0028 rods with the pistons being an average .003 in the hole. Lat time I think it was like .0025 mains and 0023 rods. I run 15w-40 oil. Hopefully it’s not too loose.

[Dragncar]

You are fine. The 455 I raced forever was a lot looser than that on the mains. Its a giant 3.25 journal, you don't want to run them tight.

[scott70]

Yes that has happened to me before with clearances too tight and wiped the bearings on the dyno. These are just a little looser than what I was hoping for. At .0023 and .0025 the bearings looked great I guess when they took it apart. I know the oil pressure might be a tad lower.

[steve25]

Go by this chart for the weight oil you should run .

Normal oil temp should not top 240 otherwise you need a cooler.

While your block is at the shop the oil galley plug below the distributor should get removed and a brass or aluminum one installed.

This way if you do want to add a oil temp sensor a 45 or 90 degree fitting can be put in for the sensor to screw into.

[Dragncar]

Originally Posted by scott70

Yes that has happened to me before with clearances too tight and wiped the bearings on the dyno. These are just a little looser than what I was hoping for. At .0023 and .0025 the bearings looked great I guess when they took it apart. I know the oil pressure might be a tad lower.

I would be happier with .0035 to .004 on those big mains. That where my 455 was set up and it had 75-60 lbs cold, 60 lbs running down the track and never got below 40lbs at idle.
Lasted 30 years too.
I would not want to run a 455 with .0025 on the mains.

[steve25]

Here’s what Federal Mogul wants you to shoot for in terms of bearing clearances for a 3.250” main and a 2.500” rod journals in a competition motor.

The middle of the spec is ideal

I have many times run .0025” on 3.250” crank mains and encountered no issues, nor problems, but your line bore needs to be confirmed to be within .0005” and most times getting this requires the block get line honed by a shop that can hold this .0005” tolerance.

If you don’t want to get your block line honed then I would try to stick to a main clearance of .0028”


Another consideration are the crankshaft oil feed holes.
Far too many shops and back yard builders think that nicely radius chamfers around the oil feed holes are a plus, but they are not.

Anything much more than what’s in this photo is detrimental to supporting the bearings.

I have seen due to my oil temp gauge that 3.250” mains produce higher oil temps and the oil temp comes up faster also.

Oil thinning out too much from excess heat produces the same bad effects as not enough oil once a certain rpm is reached.

This is what lead me on one of my 455s to install duel 2 Qt oil filters .
This alone knocked off 15 degrees of oil temp.

In fact I believe it’s GM that is now having bearing issues on new motors due to this very issue of having too large of a chamfer on there crankshaft oil holes .

Chamfers work both ways.
Too large of a chamfer also allows oil to get pushed back easier into the oil hole feed hole it came out from!

[scott70]

My race 455s back in the day ran low .003’s on the mains if I remember correctly, shifted at 6500 and didn’t have bearing problems. Can’t remember what the rods were. This particular motor I’m doing now is my street car that I occasionally take to the track and shift at 5500. It was line honed back in the day. Sounds like I should be all set with the current .0028 rods and .0029 mains. Looking through some PY past threads on bearing clearances opinions vary. I was hoping for a little tighter but I can imagine trying to get multiple batches of different bearings that technically should be all the same and wading through them trying to find a specific number to get to. Just watched a Steve Morris YT where he was getting different thickness bearings out of the same package. That must be frustrating.
The rods this time were changed to molnars so that’s one reason the rod clearances might of changed on this rebuild from last time. I can’t remember what the oil hole chamfer looks like on my crank…

[Half-Inch Stud]

I played around with 3.25 Main-Rod clearances: prefer 2.5-3.0 mil, and advice above seems better.

The big deal is oil sump to keep pickup happy.

[steve25]

Huh?

[NeighborsComplaint]

I did .0035 mains on my 455. Oil pressure would dip down to 20psi at a 750 rpm idle w a Mellings M54Dvpump. I had to pull the motor a couple years later due to a leaking rear main seal and I swapped in a Butler blueprinted SD pump and billet shaft on their recommendation w the .0035 main clearances. Oil pressure jumped right up to 45 psi at idle and 80 Psi at cruise.

[HWYSTR455]

Factory large journal cranks turn into a wet noodle at RPM, flexing all over the place, which would require larger clearances. (bind)

Main saddles flex too, but obviously not as much as the crank.

Sloppy machine work is also a situation where you run larger clearances. (safer)

Larger clearances it's best to run the 80psi spring/80 psi pump.

Higher loads and larger clearances require higher viscosity oils (and more volume/flow). Basing your viscosity on oil psi readings are not an acceptable approach.

Using the above and factoring in how the engine will be used determines the clearances to be used. You can't give 'general' advice on clearances without knowing the above info.

In short, there's a range of clearances that 'can' be used, not one specific value(s).


.

[scott70]

Originally Posted by NeighborsComplaint

I did .0035 mains on my 455. Oil pressure would dip down to 20psi at a 750 rpm idle w a Mellings M54Dvpump. I had to pull the motor a couple years later due to a leaking rear main seal and I swapped in a Butler blueprinted SD pump and billet shaft on their recommendation w the .0035 main clearances. Oil pressure jumped right up to 45 psi at idle and 80 Psi at cruise.

This time around I used the butler blueprint 60-70 psi pump and a nitemare pump shaft. I did install the washer that comes with the pump . All my engines in the past have idled around 20 psi at temperature with a standard melling 60 psi pump.

[steve25]

20 at hot idle ( under 1000 ) is plenty as long as by 2000 it slams right up to 40 to 45 psi.

[scott70]

Dyno day this Friday.
.040 over 455
9.73-1
236/244 @ .050,,,, .580 lift HR
Stock iron port matched intake
Cliff quadrajet
#64 heads cnc port to 254 cfm by Dave
Dyno headers but will switch to my rare oversized manifolds with 3” head pipes
MSD RTR
Internally balanced

With headers I’m expecting around 495 hp .

[srmmmm]

Originally Posted by scott70

Dyno day this Friday.
.040 over 455
9.73-1
236/244 @ .050,,,, .580 lift HR
Stock iron port matched intake
Cliff quadrajet
#64 heads cnc port to 254 cfm by Dave
Dyno headers but will switch to my rare oversized manifolds with 3” head pipes
MSD RTR
Internally balanced

With headers I’m expecting around 495 hp .

I'll give you 30 more hp based on my engine.

.060 over 350/413 stroker
9.34 to 1
224/230 @.050 .502/.510 lift HR
Torker-I port matched intake
6X-4 heads - stock
Hooker Dyno headers
MSD RTR

442 LbFt@4300 and 453HP@5600

[scott70]

Back in 2019 it made 491 hp at 5200 rpm and 570 trq. with the headers. So other than a slightly bigger bore the biggest difference is going from the HFT ram air 4 sized cam and rhoads v max lifters to a HR …its a little more duration and the lift went from .530 to .580. That’s why I’m not expecting much of a power increase.
I’m hoping the power loss going from headers to the rare manifolds and 3” pipes is a little less this time as last time it was regular ram air manifolds and 2.5” head pipes and lost about 15 -17ish horsepower. Maybe this time I’ll only lose about 10 ish.

[scott70]

So they got the engine running and they called and said it’s missing a little on the pull and around 5300 it would just shut down and then come back to life. They happened to have another Pontiac RTR msd dist with a bronze gear and tried that one . It ran fine with that one. I asked them to switch modules possibly to see if mine is bad. Ugh. He did say it made a little over 500 hp but didn’t have any other details at the moment. If they’re not interested in switching modules I’ll probably just buy another module have them install it and see if it works. If it doesn’t, I’ll probably just buy another ready to run and send this one off to MSD to fix it and then sell it I guess.
Once my dist is in it a running right I’ll go up ,, make some pulls and then put on my qjet, make a pull and then install the iron manifolds and see what it does for power.

[AG]

Who is dynoing the motor?

[scott70]

The same people that put it together for me,, redline performance engines. They don’t want to pull the module or anything out of the other distributor and I don’t blame them so I’m just gonna get another distributor coming. I’ve got a small body DUI distributor, but I’d have to get a different poly gear for it for the roller cam. And I kind of like the rev limiter part on the MSD so I’ll just stick with another one of those. I think the module alone is like 180 and I’m not even sure if that’s the problem. I’ll just send this one into MSD and let them fix it at their leisure.

So I’m not going over to the dyno shop tomorrow now… no sense until I get a dist I own in there and running correctly.

[HWYSTR455]

It's criminal what MSD/Holley distributors cost now, need a mortgage for those things...


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