Bearing clearances and tolerances

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I posted those already over a year ago, because Molakule was collecting data. Still don't know if the data points at my car having loose or tight clearances. I think it might be interesting to some, because the issue of clearances and suitable oil viscosity keeps coming up.

1999 Audi 2.8 V6 12 valve motor, engine code AFC

- main bearing oil clearance: 0.0007 to 0.0018"
- con rod bearing oil clearance: 0.0006 to 0.00244"
- con rod side clearance: 0.0020 to 0.0122"

piston ring end gap,
- top compression ring: 0.014 to 0.020"
- 2nd compression ring: 0.020 to 0.028"
- oil control ring: 0.0098 to 0.0197"

piston ring side clearance,
- top ring: 0.001 to 0.003"
- 2nd ring: 0.001 to 0.003"
- oil ring: 0.001 to 0.003"
 
Chevy LT1:

main bearings: 0.0008 to 0.0020"
rod bearings: 0.0013" to 0.0035"

Its not just bearing and piston ring clearances. Its also the size and number of the oilways heading up from the crank bearings (which are usually first after the pump). These oilways can bleed significant pressure off the crank bearings. I think this is where either a high pressure or high volume pump is used, and viscosity grades relevant.
 
quote:

Its not just bearing and piston ring clearances. Its also the size and number of the oilways heading up from the crank bearings (which are usually first after the pump). These oilways can bleed significant pressure off the crank bearings. I think this is where either a high pressure or high volume pump is used, and viscosity grades relevant.

I agree. Also, my oil pump can put out 200 psi. The question remains, is this an engine with loose clearances?
The other questions is, why does my manual say I can use anything from 5W-30 to 20W-50/10W-60 (according to ambient temps, of course)?
 
quote:

Originally posted by moribundman:
is this an engine with loose clearances?

you have to know the journal sizes in order to understand the bearing clearance. if it's a 1" journal, .002" clearance is huge, but for a 3" journal it's on the tight side.

for a common journal size (1.9 - 2.3 inches), though, the bearing clearances you list are on the tight side. the rod side clearances seem insanely small to me, as low as .002" is permissible?

to me "loose" is .003" on most regularly sized journals, and pistons in the .004" range on a 4" bore (assuming modern, streetable piston alloys).

-michael
 
Okay, good to know. Here is more info:

- main bearing journal diameter: 2.559"
tolerance: -0.0008 to -0.00165"

So I have an engine (very old design by now) with insanely tight clearances, a powerful oil pump, and heavier oil is preferred. Does this make any sense?
wink.gif
 
Thats something I'm wondering myself, if newer cars are really tighter clearances. My 02 VW Jetta 2.0 is a old engine design and their recommendation of thinner oils made me believe in the tighter clearance thing. Even in the service manual says that I can use anything from 5W-30 to 10W-60 even lists 20W-50.

Piston Ring Side Clearances
AEG, AVH, AZG, AWW, AWP
Top compression ring 0.06-0.09mm (0.0024-0.0035 in.)
Bottom compression ring 0.006-0.09mm (0.0024-0.0035 in.)
Oil scraper ring 0.03-0.06 mm(0.0012-0.0024 in.)

Piston Ring End Gaps
AEG,AVH, AZG, AWW, AWP
Top Compression Ring 0.20-0.40mm(0.0079-0.0157in.)
Bottom Compression Ring 0.20-0.40mm (0.0079-0.0157in.)
Oil scraper ring 0.25-0.50mm (0.0098-0.0197in.)

Main bearing oil clearance 0.0004-0.0016in.(0.01-0.04mm)
Connecting rod bearing oil clearnace 0.0004-0.0024in.(0.01-0.06mm)
Connecting rod side clearance 0.0020-0.0122in.(0.05-0.31mm)

Main bearing journal diameters 2.1260in.(54.0mm)
Tolerance -0.0008 to -0.0014in.(0.01-0.04mm)

Heres some information from the service manual, since VW and Audi engines are similar you can compare them. Some of the numbers are very close to your engine.
 
quote:

Originally posted by moribundman:
Actual oil pressure is:

17.4 - 23.2 psi at idle
43.5 - 72.5 psi at 3000 RPM


Hmmm...that isn't that high. That's about what my Supra does. I'll post the bearing clearances tomorrow.
 
lpcmidst128, that Audi engine is a pretty old design, which was discontinued in '97. The Audi 80 and 90 had that engines for a long time, before it was transplanted into the A4, only to be replaced by the 30v engine afgter a couple years. From what I hear, the old 12v already had low tension rings.

If I'd known you'd post the specs in mm, I would have done the same. I figured people weren't willing to convert.

Anyway, it's funny that VW also allows the use of pretty much any viscosity oil (well, no xW-20 oil), as long as it meets the required specs and ambient temperature range.
 
quote:

quote:Originally posted by moribundman:
Actual oil pressure is:

17.4 - 23.2 psi at idle
43.5 - 72.5 psi at 3000 RPM

Hmmm...that isn't that high. That's about what my Supra does. I'll post the bearing clearances tomorrow.

I said the pump was capable of putting putting out 200 psi, I didn't say that was the actual oil pressure.
wink.gif


Is your Supra turbo-charged?
 
Here's the specs for early 1960's vintage Alfa Romeo engines:

Piston to liner: .0018 to .0025, 2.91 bore
1st and 2nd compression ring: .0013 to .0027
Oil control ring: .0014 to .0029
Main bearings: .0006 to .0023, 2.36 diameter
Rod bearings: .0010 to .0025, 1.77 diameter
Rod end float: .0079-.0118
Camshaft bearing: .0008-.0029

These engines thrived on the specified 20W-50 oil, and ran 100-110 psi cold and 55-70 psi hot.

Newer engines have tighter clearances and need thinner oil. Yea, sure, whatever you say.
smile.gif


For comparison, here's the specs for my 1941 John Deere B:

Piston to cylinder: .004-.007 4.5 bore
Top ring: .002 to .0045
Other rings: .001 to .0035
Connecting rod: .003, 2.75 diameter
Mains .003, 2.25 diameter

This engine uses 20W-20 from 32-90F, 10-15 psi oil pressure, full flow filtration. Full load rpm is 1150 (a whopping 20.52 H.P. running on kerosene). It has enough torque to pull a house off of its foundation.
grin.gif
The engine is rated for continuous operation at 90% power.

Ed
 
A few words, oil clearance is oil clearance. Oil does not care how big a journal is, it can either squeeze into the crack asked of it or not.

however, journal overall diameter and width DOES speak loudly to the friction the oil that does get into the journal will experience.

And the faster the item in the journal rotates, friction increases proportionately to the square of the speed.

Given that most of the heat oil builds comes from the journals, size and speed play a large factor in selecting the oil quality
 
quote:

Given that most of the heat oil builds comes from the journals, size and speed play a large factor in selecting the oil quality

I have used the following viscosities in my engine over the years, but I have not noticed any difference in operating temperatures. Of course, all those oils are about the same thick at operating temp.
rolleyes.gif


OEM mystery fill ('96)

5W-50 ('96-2002)

0W-40 (2003)

5W-40 (2004)
 
quote:

Originally posted by moribundman:
I have used the following viscosities in my engine over the years, but I have not noticed any difference in operating temperatures.
OEM mystery fill ('96)

5W-50 ('96-2002)

0W-40 (2003)

5W-40 (2004)


Same here. I haven't noticed any oil temp differnces between Delvac S1300 15W-40, M1 5W-30 and M1 10W-30 in an LT-4 Chebby engine.
 
Bottom end spec's for Toyota 1FZ-FE 4.5L inline 6 used in the FZJ-80 (93-97 Land Cruiser / 96-97 Lexus LX450)

code:

Main journal diameter 2.7158 – 2.7165 in

Main journal oil clearance 0.0017 – 0.0024 in





Crank pin diameter 2.2434 – 2.2441 in

Connecting rod oil clearance 0.0013 – 0.0020 in





Piston pin diameter 1.0236 – 1.0241 in

Piston pin oil clearance 0.0002 – 0.0005 in







In the US this motor takes only 10w30/5w30 with the 5w30 being “recommended”, in other markets with identical engine you can use 5w30-20w50 depending on ambient temperature, interestingly enough in foreign markets 5w30 is only to be used in cool/cold weather below 50*f

Aus oil recommendations in *c

Engine
Petrol (1FZ-FE)
20W/50 -7 - 38
15W/40 -12.5 - 38
10W/30 -18 - 38
5W/30 -29 - 10
 
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