-
Replacing IM shaft bearings - WITH BALL BEARINGS?
by
Gizmoman
on 25 Nov, 2012 07:29
-
Calling all VW diesel gurus. . .
Has anyone ever tried using ball or roller bearings to support the IM shaft in a VW diesel? The journals would need to be turned down and bushings made for the difference. It just seems like one of the weakest areas of this motor and as far as I know, the loads are not that high. I'd have to figure out a way to insure the balls got oil and also figure out some restriction as well so it wouldn't starve the rest of the engine.
I must be missing something cause I've never heard of this mod (but am considering it on my AAZ rebuild).
-
#1
by
bbob203
on 25 Nov, 2012 07:31
-
might be a good idea but if they fall apart your engine would be all kinds a messed up.
-
#2
by
bbob203
on 25 Nov, 2012 07:35
-
also Idk if the aaz cam has the lobe on it like the 1.6 but I've read about guys getting them lightened and balanced as well as the cam and having big improvements in engine noise amd vibration.
-
#3
by
Gizmoman
on 25 Nov, 2012 08:11
-
might be a good idea but if they fall apart your engine would be all kinds a messed up
I'm with you there but there's plenty of posts here about "messed up" engines due to the stock Babbitt bearing failure. Simply over tightening the belt (even a small amount) will wipe them out in a hurry from what I've read. Then the oil pressure drops and the slow destruction begins.
BTW, the engine is an AAZ and does not have the lobe. There's not much room between the gear diameter and the bore in the block - especially on the back bushing which measures a tiny bit smaller than the front one. I think I'd have to turn a whole new shaft that would allow me to install the gear after the shaft was in (if that's possible). Maybe I could leave the rear bearing as is and just mod the nose bearing.
Does anyone know what kind of loads these bearings see?
-
#4
by
wolf_walker
on 25 Nov, 2012 12:07
-
GM made a car, think it was a special pace car edition or some such, years back that had roller bearings of some sort for the crank and/or cams it seems like. Been years ago.
While the IMS bearing wear is a real issue and has taken out many an otherwise good VW-D motor, it isn't THAT big a problem if you don't run the belt too tight for ages.
But that does happen a lot.
I think finding a good belt tension gauge and using it is an easier solution. I don't have one and have done dozens of belts, kinda wish I did but I haven't killed the IMS bearings in one yet. Though I've had some that were already fairly gone, they toddled along with very low hot idle oil pressure for many many miles afterwards. Long as the pressure jumps up with some RPM I don't sweat it too much.
And I've seen people lighten the IM shaft on these motors too, don't know how much or if any good it does.
-
#5
by
Gizmoman
on 25 Nov, 2012 12:49
-
I've read about the lightening and while it won't hurt, I doubt it has much to do with bearing life. I hear you on the belt tension and I'm confident that I can keep it within the range. It is a fairly small range though - too loose and you could smack valves - too tight and the bearings toast.
I was thinking of starting a poll to see what the average miles on one of these engines is before the bearings start dropping the oil pressure significantly. I've looked into the bearing possibility briefly and a 52 mm OD double row angular contact bearing would do it easily. A new oil seal and custom cover would be required because the shaft has to be turned down to 25 mm. The trick would be to figure out how to limit the orifice size of the oil port to the current bearing. I believe it's the fit of the babbit bearing that keeps the pressure up - the ball un-sealed bearing would let it flow to easily.
Here's a link to a possible bearing
http://www.vxb.com/page/bearings/PROD/Kit6937 - less expensive than the babbit ones!
The stock bearings (at least the front one) just seem to be a real weak point and the entire engine suffers because of it. I know it sounds crazy but it seems to be one of the weakest designs of an otherwise very strong motor and I don't think it would be that tough to try. My IM shaft already has a ding in the seal surface (from some PO) and I'll need another anyway (which I already have coming as part of a short-block).
-
#6
by
TylerDurden
on 25 Nov, 2012 13:49
-
How would the roller bearing get lubed?
-
#7
by
Gizmoman
on 25 Nov, 2012 14:35
-
Tyler,
If I have this figured correctly, the oil port in the bearing diameter could be cross drilled so it would change flow to the front of the block (once I press in the bearing, the stock port will be blocked). Then, I would machine a new cap with a mating port that picked up this oil and squirted it back into the balls. I will need to make a new cap anyway because of the smaller ID of the bearing. Porting the cap to turn the oil 180 degrees (or close) will be tricky, but I think it's doable.
As I said, I need to figure out the perfect orifice size to keep the oil pressure within range. I'm guessing a hole the size of the area (void) between a new bearing and a new IM shaft. My current shaft has .009 clearance and I think I would need to change that so it's closer to .002 or .0025". The gear end of the shaft only has .002 side-play at best.
This is kinda what started me thinking along these lines. I need to change the bearings plus I need a new shaft (seal surface has a ding). There are "pre-fit" bearings available and I've heard there were "machine to fit" ones but they may be NA. In other words, getting an ideal fit with these things is a bit of a crap-shoot and I figured, there's got to be a better way.
Just wish I could hear from someone who has already tried it.
In the meantime, I'll do some figurin' on the oil port diameter.
-
#8
by
81 vw pu
on 25 Nov, 2012 15:23
-
-
#9
by
Gizmoman
on 25 Nov, 2012 15:44
-
Interesting thought and thanks for the link. Those are needle bearings and can definitely take load. I believe they need to run against a hardened race (could be wrong here). I think the dual axial ball is a simple solution but turning the shaft down to 25 mm is a bit scary. All it's doing though is turning the vac and oil pumps. I believe the IM shaft ran the fuel pump and possibly distributor on earlier gas engines as well.
Any engineers here want to chime in on the oil porting? I did some reading and it gets a bit sticky. The bushing does not require much oil but the ball bearing will. That means I will need to let the full flow hit the ball bearing and restrict the return oil - hmmmmm.
-
#10
by
CarlosA
on 25 Nov, 2012 16:12
-
I would say you could cross drill from somewhere in the block where oil naturally drips down and have it run into the bearing that way. The major difference is that oil will always drain off the bearing causing dry starts every time. I doubt this is a BIG deal but this is why most roller bearings use grease or ride inside of a bath of oil of some sort. I think finding and adapting a better quality & thicker wall plain bearing is a good solution.
-
#11
by
libbydiesel
on 25 Nov, 2012 19:30
-
I've seen quite a few of them destroyed and yet I've seen ones that still looked good after 200,000 miles. Just don't over-tighten the belt...
-
#12
by
Gizmoman
on 25 Nov, 2012 19:42
-
I've seen quite a few of them destroyed and yet I've seen ones that still looked good after 200,000 miles
Do you know what the specs were after 200,000. Mine still "look good" but have .009 clearance on the front and .002 in the back. I don't have an oil pressure gauge (just a light for idiots) so I don't know what pressure I was running. My guess it was fairly low with that loose fit and therefore every bearing in the engine was suffering a bit.
As for the oil leaving the bearing, some should stay in the groves of the two races, and a film would remain on the balls as well. You make a good point though - maybe I could make it sit in the bearing a bit deeper by leaving one seal in the bearing (towards the engine) and when I machine the new cover, make it "hold" a bit of a bath.
Thanks for the input everyone. If anyone knows the oil flow path in an AAZ, that would help a lot.
-
#13
by
srgtlord
on 26 Nov, 2012 10:58
-
But the thing is the IM bearings are just too cheap to justify changing anything. It just takes a few spare hours, and time. 2 things in which I lack at the moment
The other result caused by overtightightening the timing belt is an Injection pump with ruined shaft bushings. There seems to be no definitive solution except to not overtighten the belt. Live and learn...
-
#14
by
Gizmoman
on 26 Nov, 2012 17:51
-
But the thing is the IM bearings are just too cheap to justify changing anything. It just takes a few spare hours, and time. 2 things in which I lack at the moment The other result caused by overtightightening the timing belt is an Injection pump with ruined shaft bushings. There seems to be no definitive solution except to not overtighten the belt. Live and learn..
That's the best reason I have heard so far - certainly wouldn't want to mess up the IP bearings - especially on a Giles pump
. You've all just about talked me out of what appears to be a silly endeavor. I fall asleep every night thinking of ways to make this engine last and the IM bearings really seem to be a weak link - can't help but try to make it go away.
The Bentley says the bearings should have .0012 to .0031 clearance. The limit is .006. My front is at .009. (with a properly tensioned belt and less than 150K on the engine), the rear is .002. As far as I know, it's the last bearing in the path of oil flow which comes from the front main.
Would anyone disagree that it's the first bearing to wear out?
BTW - I don't know your application but I'd have to drop the engine to change the bearing in the Van and I'm not fast enough to do it in less than a very valuable weekend