Block Mods- drilling mains?

Tons of motors running just like set up from the factory with zero problems. They changed the design of the motors over the years to make improvements and left this alone so I tend to follow their lead. What were the symptoms that led up to you spinning a rod bearing? High mileage, detonation, oil starvation? I pounded a rod bearing out years ago but never spun it with intense detonation before I had a scan tool. Never had a problem since with a proper resize of the rods, ARP bolts and bearing oil clearance of .0015"-.002". Don't believe everything you read.
 
The engine had about 1000 miles on it and all the clearances were between .001 and .0015. No signs of detonation or or anything else wrong. Rebuilding it to factory specs didnt work. Need to try something else or find some different options. Anybody else have an oppinion?
 
Why did it spin the bearing? Were the rods resized? Low oil volume? Bad or broken bolt, etc.? The question of why the bearing failed need to be answered before making any mods..
 
We havent seen any reason for the rod bearing failure. Yes, the rods were resized and had new bolts. The oil pump made good pressure and is a high volume style front cover.
 
i would think that having larger oiling holes could only help in lubricating the rods.
 
I had it done to my engine, my machine shop drilled them out to 5/16". Both Ruggles and the Power Source book recommend doing this. The Ruggles thing I've got says it is "mandatory" to drill them out to 3/8". The Power Source book says 3/8" in one spot and 3/8" or 5/16" in another spot, and it says that "enlarging the holes improves the condition of rod and main bearings." My machine shop did 5/16" because 3/8" just looked so dang big, esp. compared to the stock size passages. Also, #2 and #3 each feed two rods each, while #1 and #4 passages only have to feed 1 rod each, so it makes sense that they might need to be a little bigger. At least to me.

And while they are messing arround with that, since everything has to get cleaned anyway, porting (ie rounding off the sharp edges of the corners as much as you can) the passages behind the plug on the pass. side of the #1 cam bearing and where the oil comes into the block from the timing chain cover (by the oil pressure sender hole) has got to help some too. Those two spots are fairly easy to get to, and when you look at the turns the oil has to make there, you'll see it makes perfect sense to do that.

Whether or not that fixes your problem I don't know, but I think it's good practice in general.

John
 
John,
Are you running a HV pump with the drilled mains? What is your oil pressure (if the motor is done)?
One more question somewhat of topic....
Are you doing anything to address the front cam bearing journal groove? Some have mentioned it as a place oil pressure/volume is lost. Spray welding the journal or ordering a custom cam without the groove seems to be the answer.

Thanks in advance............
 
Jeff -

I am running a stock pump with a booster plate. I have a PT&E turbo saver and a 3 plate EOC in the rad (ie bigger than the stock EOC). Did lots of porting to the oil passages in the timing cover and the block. Oil filter bypass is plugged in the oil pump cover. Cam has the groove in the journal, would have liked to had it welded up, but didn't. Running TA Perf's cam bearing in the #1 spot because I had too much wear with an aftermarket replacement (not sure what brand that one was). The TA Perf cam bearing only has one oil hole for #1, located about 4 o'clock in my installation. I run 10W-30 oil, and at hot idle (750 rpm programmed, also got a 180F thermo, gotta change that one of these days) I see 20 psi during the summer, 25 psi right now. At 55 mph I see a tad less than 60 psi, at 60+ mph I see 60 or a bit more. Not sure which spring I have in the relief valve. Oil pump end clearance is 0.002" I think, could be a bit more. I spent a long time trying to get it tighter, but everytime I did it would bind a little when I turned it by hand. Idler gear has a hole drilled in it. Gears themselves are standard auto parts store units, nothing else special done to them. Engine is fairly fresh rebuild, not sure of the miles I have on it now, less than 10k that's for sure, so I can't report on the long term effects of any of that. I can say that the #1 cam bearing installed by the machine shop had a lot of wear for the short time it was in there, glad I swapped it for the TA Perf one. I think I loosened up the oil pump clearance a little at that time too. I spent way too many hours on that thing... That's everything I can think of.

John
 
Originally posted by Kansas T
How many people are drilling the main bearing oil holes like described here:
http://www.gmhightechperformance.com/tech/0205gmhtp_buick/

I spun a rod bearing and am trying to come up with the fix so I dont spin another. The Machinist suggested this.
Click to expand...

I'm building a motor right now as well, read the same article and had the same questions. Like so many things, there will be differing opinions, but here is what I got from my guys. The machinist is a race guy, and very familiar with the turbo Buicks. He's never done it, and had no history of problems. Billy Duke, our local Buick guru (runs an 8 sec GN) builds tons of these cars, beats 'em hard. Never done this. Lastly, my tech who is doing the assembly work has been a GM dealership tech for 23 yrs and built lots of race cars. His turbo-specific experience includes being a Calloway-cert. tech. Anyway, I thought his opinion was the most insightful. GM spends millions on engineering these things, and most often does things for a reason. The middle two holoes are smaller to maintain equal oiling/keep pressure up to the front and rear mains. Makes sense to me. I decided against this mod.

Good luck w/your build
 
Re: Re: Block Mods- drilling mains?

Originally posted by John Purdom
GM spends millions on engineering these things, and most often does things for a reason. The middle two holes are smaller to maintain equal oiling/keep pressure up to the front and rear mains.
Click to expand...

Agreed with the differing opinions on the subject :) I certainly don't think it is required, just that it is a good idea in general.

The Power Source book was put out there by GM, and it says it's a good idea, so I don't share the concern of it not being factory approved.
Also, since the two middle holes feed 1 main + 2 rods while the 2 outer holes feed 1 main + 1 rod, I'm not sure why the inner holes need to be smaller. They need more flow, not less.

The factory did lots of things half-assed. This might be one of them, it might not, kinda hard to say. Someone may have made these two passages smaller for a reason, but it might not have been a *good* reason, if you know what I mean. :) They make mistakes too...

John
 
John,
Thanks for the run down. I am about to pull apart my motor that has about 10K miles on it. I put in friction coated race cam bearings (suppose to be harder then the non race versions for lots-o spring pressure). I am curious to see what that front bearing looks like. I put the race bearing set in because I too had concerns about that front bearing even though I run a stock volume pump.

Thanks again,......................
 
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