Opinions on rod and main bearing clearences

[karolko]

I have read alot of the previous post in regards to bearing clearences, but i was hoping some of the good-old-boys (no, not Bo and Luke Duke) could step in and shed some light on what type of bearing clearences we should be telling our engine builders to use?

From what i have read and remembered, our engines came speced from GM with 0.0015-0.0018 clearences.

So here is where it is going fun, most of us run moderate- to highly modified engines in our buicks, so what should we run for clearneces when making much more power than what our factory number were like.

I myself am in the process of getting the block built by the machinist around town, but i do not trust his typical Chevy train of thought. I beat the hell out of my car on the street, but it is still a street vehicle, and i am planning on 5-600 hp to the wheels.

The machinist will be doing the bottom end this coming week, so numbers would be awesome..

Please advise.

 

[bosted86]

i believe there is a spec sheet for all of the clearences on gnttype.org.

 

[Lee Thompson]

I keep mine @

.001----.0015 max. Rods and mains.

 

[Just a Six??]

Take the numbers then tell him on the tight side.

 

[karolko]

what numbers? 0.0015 or my machinists? my machinist says to 0.0027, which i think is way too tight.

 

[Alky V6]

.001----.0015 max. Rods and mains.

I'm going to stay out of this one. There are so many variables involved in picking the clearances to use. I am curious about Lee's though. Lee, can you tell us a bit more about your combo?

Block type? Girdled? Steel caps?
Oil type and weight?
Max RPM level?
Type of bearings?
Type of crank and rods?
Power level? Boost level?
Type of fueling? Alky injection?
Special break in procedures?
Oil pump volume? Pressure?
Oil capacity?

I know. It's a little more than a bit. Sorry for being the curious cat. Thanks for sharing Lee.

 

[Alky V6]

what numbers? 0.0015 or my machinists? my machinist says to 0.0027, which i think is way too tight.

I would treat .0027 as a max for crank or rods on an iron block. I'm using clearances in the range of .0015" to .002" on the mains (aluminum block) and .0022 to .0027" on the rods. But then, I'm spinning the beast a bit more than most everyone else. I also use a heavy oil with the alcohol.

karolko. You have a habit of starting some interesting threads.

 

[Just a Six??]

what numbers? 0.0015 or my machinists? my machinist says to 0.0027, which i think is way too tight.

How many GN's has this guy built? What kind of power? Does he stand behind his work 100% How long have you known him? Have you talked to other GN owners with his motors? What do they say? If you can answer these questions & have complete faith in him then let him do what he likes?
My builder has done at least 100 GN's (probably double that!) all 500-750 HP & No Complaints as I ask everyone. Done 5 for me so now I just drop it off & pick it up. First time my spec sheet said 15-18 on the Tight End!! He agreed.
These things need to be tight but still the factory specs are a good guideline unless your using some real HD parts with Racing Only in mind & then I wouldnt know what to suggest. I'm talking 600HP with some city & some track days with a low 11 high 10 at the track. Still on the street I want driveable with AC etc. Hope this helps but make sure you TRUST him & his work! Thats the Key here!!

 

[Alky V6]

What weight oil do you plan on using?

 

[gnxtc2]

I would treat .0027 as a max for crank or rods on an iron block. I'm using clearances in the range of .0015" to .002" on the mains (aluminum block) and .0022 to .0027" on the rods.

Same here....:wink:

I switched from using Rotella 15w-40 to a racing 20w-50 oil.

Billy T.
gnxtc2@aol.com

 

[karolko]

Hello Again,

to answer some of your questions, I was recommended to this machinist from a close friend of mine. he had his stage II built by him and he is pushing 900+hp on his setup. The Machinist is known for making high hp engines, so his skills are not what i am worried about it is how many of these buick motors he has built. The stgae II motor was running a Duttweiler sp? oiling system, so bearing clearences were different for him then what i will need.

He stands behind his work and offers a warrentee on his work as well, but i just don not want to go through the hastle of taking my car out for another season.

Don, thanks for the compliment

Block type? Girdled? Steel caps? 109, rjc girdle, with billet caps
Oil type and weight? i don't know, do you run
Max RPM level? 6000rpm
Type of bearings? is there a difference
Type of crank and rods? eagle crank, K1 rods
Power level? Boost level? 500-600hp and 20-24lbs on the street and 28-30 at the track with c16
Type of fueling? Alky injection? 83lbs injectors with alky control
Special break in procedures? have no idea how to break in the motor?
Oil pump volume? Pressure? i think i have one of those boost plates? previous owner
Oil capacity? i have the standar oil pan plus the 3/4 for the girdle.

My machinist said that if i run too looser tolerences, nothing bad will happen, the oil will just take up the slack, but i even know if the clearnece is too big, then no oil pressure!!!

let's here it boys. where are the big dog engine builders when you need them. they might be getting a nagging phone call from me on monday...

 

[Alky V6]

I use 25w-50 racing Pennzoil. It's a special oil that is designed for use with nitro and alcohol applications.

The reasons for my oil choice were:
Main and rod clearances. On the looser side.
High rpm operating range. 4,500 to 7,500 rpm. 7,800 rpm redline.
Needed an oil that wouldn't be quickly attacked by the alcohol in the blowby.
Looser clearances will tolerate any moving around or distorting of parts at high loads and/or high rpm.

Generally, you want to run thicker oils with larger clearances. Thinner oils with tight clearances. That way the rate of flow through the bearings is controlled for proper lubrication and cooling of the bearing surface.

 

[Lee Thompson]

reply

I'm going to stay out of this one. There are so many variables involved in picking the clearances to use. I am curious about Lee's though. Lee, can you tell us a bit more about your combo?

Block type? Girdled? Steel caps?
Oil type and weight?
Max RPM level?
Type of bearings?
Type of crank and rods?
Power level? Boost level?
Type of fueling? Alky injection?
Special break in procedures?
Oil pump volume? Pressure?
Oil capacity?

I know. It's a little more than a bit. Sorry for being the curious cat. Thanks for sharing Lee.

Stage II --274
10-40 --couple syn. rest regular
6200 rpm
I have some left over wide V rod bearings in .001 and .002 under
Federal Mogal mains
BMS 3.625 finished by Moldex
Carrilo 6.5 rods
J and E pistons
8.3 CR
25 psi with alky injection
No special breakin
Stock wet sump with deep pan and blueprinted cover
25 hot idle with around 55 @ cruise
9 quart total (remote filter and a large external cooler) No rad. cooler.
i go to the track a few times a year and I DO drive my car.

 

[karolko]

wow, it seems that no one here using rod and main bearings. wow?!?

 

[karolko]

Can someone explain WHY buicks must run tighter clearneces than regular engines????

Numbers are numbers, but reasoning is something else, so there must be a reason why there tollerances are tighter.

 

[Alky V6]

This is directly out of the Buick Power Source book.
Main bearing clearance: .0022-.0027"
Connecting rod bearing clearance: .0018-.0022"

Building up a Buick V6 is not as picky as some people make it out to be. It really isn't any different than building up any other high performance engine. If you understand the principles and variables of blown high performance engine building you will find that they all apply to the Buick V6. No special magic. No special clearances. Much is just what the engine builder prefers.

 

[Lee Thompson]

Lets see

Can someone explain WHY buicks must run tighter clearneces than regular engines????

Numbers are numbers, but reasoning is something else, so there must be a reason why there tollerances are tighter.

One reason is the fact that we have a 1/4 in. leak built into the system.
Another is the many 90 degree turns that is in the oil path.

I believe the power source mostly applys to all out race eng.---roundy round or drag eng. Anyway, something that turns high RPMs. If you run .002--.0025 on a street eng. without some kind of FIX, you won't be happy. My opinion.

 

[Troubled81]

is the 1/4 in leak refering to the turbo oil feed line?

 

[turbodave231]

I got to agree with Lee on this one. The stock V6 was not blessed with an outstanding design for an oil pump. Aluminum housing with iron gears, multiple 90 degree turns and a long pickup tube/passage. Blueprinting the front cover and gears really helps. But that small pump has to work very hard to cover up huge clearances and oil a turbocharger.

I prefer to set them up tight.......and I've never lost an engine due to lubrication problems.

 

[Lee Thompson]

yes

is the 1/4 in leak refering to the turbo oil feed line?

Yes. Granted it probably don't leak a full 1/4 in.--- but could.