Missy Good Wench
Wild Blonde from Cloud Mt
There is always a lot of chatter about the bearing and piston clearances on these engines.
These are metric engines and everything on them, save a couple things like the bellhousing bolt holes on the pre 96 stuff is metric.
The specs book all call out the clearances in MM.
This is not a big issue, but here in the States, we are used to measuring in Inches.
Here are some good hard numbers that you can take to the bank.
Piston clearance
Cylinders 1,2,3,4,5,6 can be set at .004" and work very well
Cylinders 7 & 8 run a tad hotter and will be very happy at aroound .0045"
The book does give slightly lower numbers on these as minimums but, dont take a chance with a scuffed piston, use the numbers as mentioned.
Bearings are all over the sky on these and GM used a select fit process whereby they intermixed the upper and lower shells to produce the fit they wanted.
The shells will be stamped with numbers on the back of the insert that reflect the date they were made and the part number and also the size.
A common notation is .013 US this is MM and denotes that the particular shell is .0005" undersize (Half a Thou)
Many times the upper and lower shells will be different to suit the need.
STD on the upper and .013 US on the lower.
The rods can also see this same scheme.
Now out here in the real world, these select fit bearings are really not available other than Ma General and then at $$$$$$$$
Forget the fancy select fit stuff and stick with the good O'l standards or other sizes if the crank has been ground.
A good place to be is at .0025" on both the rods and the mains.
You really don't want to be any tighter but you could be a slight bit looser and still be fine
Mains at .003" would not scare me at all. Rods at .0025 are right in the sweet spot.
If you are running the bottom end at the outer limits and find that the Oil pressure is a tad low at idle in really hot weather, you can either step up a grade on the oil or do as I have always done, add a can of STP during the hot weather.
Oil pressure on these things always seems to worry some folks.
The bearing diameters on these engines are fairly large compared to say a chevy Mouse Motor. In such, the oil pressure over the large bearings does not need to be really high.
Hot running at 40PSI is great and Idle hot at 20 PSI is fine.
The normally recommended 15-40 diesel rated oil is perfect for these and should serve well in all but the worst desert conditions.
Under super high temps, you might want a little higher viscosity oil ????
I have run these engines in Southern California heat of the summer and never had issues.
As I have mentioned in another post, the practice of using a squirt block pump on a non squirt block will raise the oil pressures to much higher levels.
75-80 cold and 55-60 running hot and idle at 35
The overall picture of this is not bad, the issue could be the high pressure when the temps dip LOW.
My only concern would be the cooler/lines.
If you have uprated your cooler and the lines to something a bit better than stock, then the high pressure wont hurt anything.
I always felt warm and fuzzy watching the Oil pressure running along at 55-60 PSI going down the Boulevard.
Now the 80 PSI at idle on a cold morning and who knows what when reved up always made me a tad nervous.
After seeing how cheezy the factory cooler lines are, the stock pump is likely a better choice.
Hope these thing are useful to someone.
Missy
These are metric engines and everything on them, save a couple things like the bellhousing bolt holes on the pre 96 stuff is metric.
The specs book all call out the clearances in MM.
This is not a big issue, but here in the States, we are used to measuring in Inches.
Here are some good hard numbers that you can take to the bank.
Piston clearance
Cylinders 1,2,3,4,5,6 can be set at .004" and work very well
Cylinders 7 & 8 run a tad hotter and will be very happy at aroound .0045"
The book does give slightly lower numbers on these as minimums but, dont take a chance with a scuffed piston, use the numbers as mentioned.
Bearings are all over the sky on these and GM used a select fit process whereby they intermixed the upper and lower shells to produce the fit they wanted.
The shells will be stamped with numbers on the back of the insert that reflect the date they were made and the part number and also the size.
A common notation is .013 US this is MM and denotes that the particular shell is .0005" undersize (Half a Thou)
Many times the upper and lower shells will be different to suit the need.
STD on the upper and .013 US on the lower.
The rods can also see this same scheme.
Now out here in the real world, these select fit bearings are really not available other than Ma General and then at $$$$$$$$
Forget the fancy select fit stuff and stick with the good O'l standards or other sizes if the crank has been ground.
A good place to be is at .0025" on both the rods and the mains.
You really don't want to be any tighter but you could be a slight bit looser and still be fine
Mains at .003" would not scare me at all. Rods at .0025 are right in the sweet spot.
If you are running the bottom end at the outer limits and find that the Oil pressure is a tad low at idle in really hot weather, you can either step up a grade on the oil or do as I have always done, add a can of STP during the hot weather.
Oil pressure on these things always seems to worry some folks.
The bearing diameters on these engines are fairly large compared to say a chevy Mouse Motor. In such, the oil pressure over the large bearings does not need to be really high.
Hot running at 40PSI is great and Idle hot at 20 PSI is fine.
The normally recommended 15-40 diesel rated oil is perfect for these and should serve well in all but the worst desert conditions.
Under super high temps, you might want a little higher viscosity oil ????
I have run these engines in Southern California heat of the summer and never had issues.
As I have mentioned in another post, the practice of using a squirt block pump on a non squirt block will raise the oil pressures to much higher levels.
75-80 cold and 55-60 running hot and idle at 35
The overall picture of this is not bad, the issue could be the high pressure when the temps dip LOW.
My only concern would be the cooler/lines.
If you have uprated your cooler and the lines to something a bit better than stock, then the high pressure wont hurt anything.
I always felt warm and fuzzy watching the Oil pressure running along at 55-60 PSI going down the Boulevard.
Now the 80 PSI at idle on a cold morning and who knows what when reved up always made me a tad nervous.
After seeing how cheezy the factory cooler lines are, the stock pump is likely a better choice.
Hope these thing are useful to someone.
Missy
