408 Main Bearing Clearances

[Jetsurgeon]

Hi, starting to assemble my block, the specifics are:

408 CI 10.5/1 Compression ratio (calculated)
Balanced Scat cast crank and forged rods and pistons
Edelbrock RPM heads, ported, Manley Race Flo valves with PAC springs
Flat tappet cam/lifters, 1.6 ratio roller tip rockers, cam has over .600 lift
Direct port fuel injection
Block decked, bored/honed, and mains align honed.

Here are the measurements I got for the main clearances, using a .0001 dial bore gauge and then followed up with Plastigauge to double check (pretty accurate BTW)....#1 is at the front

#1 .0025
#2 .0025
#3 .0024
#4 .0030
#5 .0019

A little odd, especially the #4 and 5 being so different....my question is, would you change anything? #5 is pretty thin.... Hi volume or standard oil pump? It is a "Hot" street build....

Thanks...

 

[Steve340]

Assuming those measurements are correct and it sounds like they are as you post you have double checked.
#5 would be a little tight. The rear main generally needs a little more clearance.
Blueprinted standard pump will be fine. The gear rotor style are so much better than the spur gear type.

 

[Chryco Psycho]

you could swap brgs between 2-4 or 4-5 to see if the clearance changes ,
I would use aa high volume pump only if you have a larger oil pan otherwise high pressure only .

 

[Jetsurgeon]

you could swap brgs between 2-4 or 4-5 to see if the clearance changes ,
I would use aa high volume pump only if you have a larger oil pan otherwise high pressure only .

I will give that a try, I am planning a 7 Qt Milodon Oil Pan, looking at the Low Pro 30941, as with my setup I expect to be up to 7K RPM....which is why I want the bearing clearances to be right

 

[FY1TopBanana]

Surgeon, This is pretty much your build. As Chryco suggested I would try swapping to improve #4.
#5 is definitely too tight.
Did you check the journal and see if it is the culprit? A machine shop could dress the #5 journal to open up the clearance or there's always the .001 oversize shell option.
FWIW my 408 oiling has the Milodon road race pan, Melling high volume pump, and 340 T/A 90 deg oil filter.

Btw, you A&P with that handle?

 

[Jetsurgeon]

You know, I did not check the bores before I put the bearings in...it was just align honed, so figured they should be pretty close to the same....

Yes, I am an A&P

My 72 that this engine is going in is an original FY1 Rallye 4 spd Feel free to send more pics of yours !!

 

[FY1TopBanana]

That's a 72 Demon with the 408. My Challenger is a 426 Hemi on a 72 service block with Callies forged 4.5 crank with Eagle h-beam 7.1 rods (big rod angularity, long dwell) with a .040 overbore = 518 ci. Stage V top end complete to valve covers.
Pretty mild cam that was originally for 727 2500 stall so it gets 12" idle vacuum here at 6500'. Was 680 flywheel on dyno at SL.
It has a Passon 833 18 spline overdrive in it now.

I'm ATP and used to make the mess for my A&Ps. Brought a Falcon 50EX home one day with a lightning strike - my Chief wasn't happy. Vaporized all the radome bonding and exited a couple left wing static wicks - also vaporized. Expensive but the bird performed. Actually have all the practical covered if I ever wanted to get the A&P but without IA not much use. May be a homebuilder (RV-14) someday.

The Challenger electrical is total rewire with aircraft design. Used Infinitybox canbus power mgt and distribution, busbar battery, main 200a relay batt main, push to start, "avionics bay" rear panel, etc etc.

Best on your project. Shout if I can help. - Bill

 

[Jetsurgeon]

OK, I swapped 2 and 4 bearings and it did help, also remeasured EVERYTHING with the dial bore gauge (right, left, front and back of each bearing half) and this is what I have...still don't know what to do about #5 on the left side...:

	Front	Rear
#1
L	0.0023	0.0024
R	0.0024	0.0022
#2
L	0.0025	0.0027
R	0.0022	0.0022
#3
L	0.0025	0.0024
R	0.0021	0.0023
#4
L	0.0025	0.0022
R	0.0025	0.0024
#5
L	0.0014	0.0014
R	0.0021	0.002

 

[Steve340]

Have you actually measured the crankshaft? It must be slightly bigger on #5 or the bore is smaller.
As FY1 mentioned you may need to get the crank journal polished smaller.

 

[Jetsurgeon]

Have you actually measured the crankshaft? It must be slightly bigger on #5 or the bore is smaller.
As FY1 mentioned you may need to get the crank journal polished smaller

Have you actually measured the crankshaft? It must be slightly bigger on #5 or the bore is smaller.
As FY1 mentioned you may need to get the crank journal polished smaller.

Hi, well, honestly I had just measured the #1 journal, locked the mic, and checked the others and they were all pretty snug, so I used that as my base to set the dial bore gauge. I just went and measured each journal and the difference was -.0003 to -.0004 different. Not very significantly different. The #1 measured at 2.8100, the rest were 2.8097 or 2.8098....

 

[Steve340]

Well that sounds OK. So long as the bearings have enough crush in the bores the block should be OK.
If all that checks out to your satisfaction - go to a machine shop and have them polish the rear journal.
I think I read earlier you want to rev it to around 7 thousand.
I would increase the rear main clearance to 3 thousands.

 

[Jetsurgeon]

Well that sounds OK. So long as the bearings have enough crush in the bores the block should be OK.
If all that checks out to your satisfaction - go to a machine shop and have them polish the rear journal.
I think I read earlier you want to rev it to around 7 thousand.
I would increase the rear main clearance to 3 thousands.

And I just got the block back from the machine shop after all the work including having the mains align honed.....

 

[Steve340]

At least it is tight - not flopping around loose.
Lucky you checked.