The pilot bushing is a VERY important part in the 2.5 engine. It helps locate the flywheel or the torque converter and keeps it centered on the crankshaft. THIS BUSHING IS VERY IMPORTANT do not skip the installation of it. I did and it COMPLETELY destroyed my transmission.
Here are the part numbers.
Part number listing from the 84-88 P Fiero 22P microfiche: It would appear the words "insert" and "pilot bushing" are one in the same. The part numbers are in line with the earlier listing I posted, except it includes 87-88.
84-87 P Engine Asm - 2.5 L4 (LR8/2.5R)
Spacer, Flywheel to Crankshaft - 10005655 Insert, Cr/Shf - 10018699
88 P Engine Asm. - 2.5 L4 (LR8/2.5R)
Spacer, Flywheel to Crankshaft - 10005655 Insert, Cr/Shf (W / M.T.) - 10009785 Insert, Cr/Shf (W / A.T.) - 10018699
Crankshaft Flange Inserts on GM 2.5L (151 CID) Engines
General Motors Corporation uses 3 different crankshaft inserts on their 2.5L (151 CID) engines.
These steel crankshaft inserts are pressed into the tail end of the crankshaft and provide support for a pilot bushing on vehicles with manual transmissions or directly support the nose cone of the torque converter on vehicles with automatic transmissions.
Use the following chart and diagrams when selecting a replacement crankshaft or steel crankshaft insert:
Crankshaft Pilot Bushing Update On 1979-93 GM 2.5L Engines
The AERA Technical Committee offers the following information regarding an update on crankshaft pilot bushings for 1977-93 GM 2.5L engines. Previously, AERA published Technical Bulletin TB 477R. The information in this bulletin is to be used in addition to that bulletin. GM has used six unique crankshaft pilot bushing inserts for their different 2.5L engine applications.
These inserts are pressed into the rear of the crankshaft and provide support for either the input shaft of a standard transmission or direct support of the torque converter hub of an automatic transmission. Use the following chart and diagrams when selecting a replacement crankshaft insert, keeping in mind GM also supplied engines to the Jeep Corporation for postal use:
Model Year Drive Model Part # View 1984-86 RWD Fiero w/ automatic trans. 10018699 C 1984-86 RWD Fiero w/ manual trans. 10009785 B 1
It is recommended to inspect all crankshafts to ensure that the proper insert is installed to match the desired application. AERA is currently aware of several aftermarket suppliers for some of the above mentioned inserts.
The AERA Technical Committee
Many thanks to FrugalFiero for gathering this information.
quote
Originally posted by KurtAKX: Here's what the pilot bearing does: This is a picture of an iron duke flywheel installed on the back of a crankshaft which has a FACTORY INSTALLED pilot bearing in it. The engine is in a "normal" orientation. The only thing holding the flywheel on to take this picture is the "snug" fit of the flywheel bore being piloted by the bearing. It is the only feature which keeps the flywheel centered; there are no dowel pins or shoulder bolts to do the job!!!
If you don't believe me, pull out your Iron duke and do the following: 1) Get a measurement off the flywheel bore 2) Take calipers over to pilot bearing; note that bearing diameter is the same as flywheel bore diameter (duh, that's why it was put there for stick cars.)
MANY thanks for your efforts in getting this very valuable information. I don't know what I would do without this forum and the good people on it, it really is a god send.
Thanks...
[This message has been edited by 84Bill (edited 11-19-2008).]
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05:46 PM
PFF
System Bot
GT86 Member
Posts: 5203 From: Glendale, AZ Registered: Mar 2003
Just read Kurt's post in the other thread. I think he is on to something. If I understand what he is saying correctly, the duke uses a bushing in the crank for proper alignment/centering of the flywheel. Without the bushing, the flywheel will most likely be off center and cause catostrophic bolt failure esulting in the flywheel coming off the crank.
Possible if the flywheel has no self centering ridge on it, but the pilot still has nothing to do with the tranny. I would think that would be a rare flywheel. I've never seen a flywheel center on a pilot either, but it sounds plausible..
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12:02 AM
GT86 Member
Posts: 5203 From: Glendale, AZ Registered: Mar 2003
Just read Kurt's post in the other thread. I think he is on to something. If I understand what he is saying correctly, the duke uses a bushing in the crank for proper alignment/centering of the flywheel. Without the bushing, the flywheel will most likely be off center and cause catostrophic bolt failure esulting in the flywheel coming off the crank.
I guess the 6 bolts that are used to hold the flywheel to the crank have nothing to do with its alignment. I guess a bushing that isn't a tight fit to the flywheel provides alignment.
If you are speaking of an automatic, then there is a piece that looks a lot like a pilot that is used to help align (but not support) the torque converter.
Both of these threads need to be locked and deleted so that they don't pollute any further.
[This message has been edited by GT86 (edited 11-18-2008).]
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01:39 AM
Will Member
Posts: 14250 From: Where you least expect me Registered: Jun 2000
I've never played with an iron duck, but I've never seen a crank that didn't have the flyhweel pilot integral with the crank flange. Crazy.
Will is correct, the flywheel bolts DO NOT align nor are they intended to align the flywheel to the crank. I have seen the crank with the sheared bolts from the other thread (which needs to be put in the trashcan, btw, and I don't understand why there is no feature on the back end to align the flywheel. Every clutch I've ever done, there was a hub to center the flywheel to the crank. Perhaps that is an auto trans crank? I don't know if they are different, I have not seen a Duke engine from an auto so I can't say.
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09:35 AM
86GT3.4DOHC Member
Posts: 10007 From: Marion Ohio Registered: Apr 2004
How do the V6 engines compensate for a lack of a bushing then?
I'll entertain this idea, it was completely impossible on so many diffrent levels before, but this is plausable, Ive got nothing against being wrong, sell me on it, or better, show me.
Well take a look at a pic of the flywheel from the other thread:
The center hole of the flywheel would require a pilot bushing with a huge O.D. to center the flywheel, would it not? The pic of the pilot bushing at The Fiero Store doesn't look anywhere near that large:
Well take a look at a pic of the flywheel from the other thread:
The center hole of the flywheel would require a pilot bushing with a huge O.D. to center the flywheel, would it not? The pic of the pilot bushing at The Fiero Store doesn't look anywhere near that large:
Well, this thread sure is a lot cleaner to work on, but we probably shoud be back on the other, but what the heck
I am not for or against this idea yet, but from my experiences, the pilot bushing would go into the smaller hole in the middle of that crank. If it did go in the outer hole, it would be huge, but it would also probably be the right size to catch the flywheel. I dunno, it would seem duke's are strange beasts indeed.
Maybe?... Not to stir the fire, but this is what is considered PRODUCTIVE conversation. The introduction of a new idea to be evaluated.
[This message has been edited by 86GT3.4DOHC (edited 11-18-2008).]
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10:47 AM
Will Member
Posts: 14250 From: Where you least expect me Registered: Jun 2000
How do the V6 engines compensate for a lack of a bushing then?
I'll entertain this idea, it was completely impossible on so many diffrent levels before, but this is plausable, Ive got nothing against being wrong, sell me on it, or better, show me.
The V6's (and every other engine I've ever dealt with) have a shoulder on the crank flange that locates the flywheel with no additional parts.
Originally posted by Will: The V6's (and every other engine I've ever dealt with) have a shoulder on the crank flange that locates the flywheel with no additional parts.
the 2.5 has no such shoulder to locate the flywheel.
[This message has been edited by 84Bill (edited 11-18-2008).]
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11:02 AM
TONY_C Member
Posts: 2747 From: North Bellmore, NY 11710 Registered: May 2001
The V6's (and every other engine I've ever dealt with) have a shoulder on the crank flange that locates the flywheel with no additional parts.
What Will said...the pilot bushing doesn't locate the flywheel, there is a turned down shoulder on the crank that fits inside the flywheel center hole, just like the way a brake rotor fits on a hub.
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11:03 AM
Will Member
Posts: 14250 From: Where you least expect me Registered: Jun 2000
What Will said...the pilot bushing doesn't locate the flywheel, there is a turned down shoulder on the crank that fits inside the flywheel center hole, just like the way a brake rotor fits on a hub.
According to the picture posted above, the iron duck does not have such a shoulder.
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11:50 AM
86GT3.4DOHC Member
Posts: 10007 From: Marion Ohio Registered: Apr 2004
Well, after spending about an hour searching three diffrent parts stores, not a one listed a pilot bearing for the duke, not a book had an entry for it, nothing. And that's not just computers, the actualy manufacturer's spec books too. That being said, I dont stand on other people's information alone, we all know they can be wrong, but finding universal results acrost several diffrent parts stores and several diffrent parts manufacturers is a very strong indication.
BUT, I did find one clutch kit that had a pilot bearing, for the 84 Fiero 2.5L, and this is its story...
And an 84 Firebird 2.5 L clutch set. It had 2 bushings, both pictured here, one is identical to the Fiero clutch set bushing.
Firebird above, Fiero below, showing needed diameter for the shaft to fit into the bushing, as well as the depth of the bushing
Now the books did list 2 diffrent bushings for the 2.5 Firebird, and accordingly, I found the 2.5 firebird clutch set above to have 2 diffrent bushings, the larger being identical to the Fiero clutch kit bushing. I dont have the depth of the crankshaft bore, but it doesnt much matter, its not large enough to touch the flywheel if it did extend, and the ID is completely too small to hold the input shaft. If someone measures the depth of the outer hole on a duke crank, we can confirm that it would not be long enough.
My ruling, even without measurements of a flywheel (which no one stocked) it appears the bushing is not large enough to touch the flywheel, nor long enough to extend past the crank.
[This message has been edited by 86GT3.4DOHC (edited 11-18-2008).]
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12:45 PM
86GT3.4DOHC Member
Posts: 10007 From: Marion Ohio Registered: Apr 2004
I would estamate the depth of the pilot bushing at ~ .6 - ~.8" Its definitely bigger than its bore, and smaller than its OD. From the picture above, I do not believe it would extend from the crank. I also do not believe it would fit in the outer hole, it appears to fit in the deeper inner hole.
I am not deflecting, if anyone takes actual measurements of the crank holes, I WILL go back and measure the depth, but without those measurements, the depth is pointless, and it can be estamated close enough from the pictures for now.
In the engine I replace the pilot bushing was not inserted all the way back into the crank bore. As I recall there was at most 1/2 inch behind the inserted bushing.
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04:19 PM
PFF
System Bot
86GT3.4DOHC Member
Posts: 10007 From: Marion Ohio Registered: Apr 2004
In the engine I replace the pilot bushing was not inserted all the way back into the crank bore. As I recall there was at most 1/2 inch behind the inserted bushing.
Okay, thats possible, that still leaves it out there hugging air. Its too small OD to touch the flywheel, and to small ID for the shaft to go into it. Check out my post here https://www.fiero.nl/forum/F...2/HTML/096400-5.html detailing the reasons why.
And, from everything I know, that would have been installed incorrectly. IIRC, the pilot bushing should be seated to the rear front (depends on which way you think about it) of the crank bore, else it will contact the tapered area of the input shaft when installed in a RWD application, which I would image would cause the transmission not to contact the bellhousing of the engine.
That is unless someone measures the ID of the flywheel and finds it to be 1.09" +/+ .05". But from appearances, that will not be the case.
Originally posted by 86GT3.4DOHC: the pilot bushing should be seated in to the rear of the crank bore, else it will contact the tapered area of the input shaft when installed in a RWD application, which I would image would cause the transmission not to contact the bellhousing of the engine.
I can assure you that it was not all the way in, I rented a pilot bushing puller that has 1/4 inch fingers to grab the back side of the bushing and there was lots of room to spare. At least... at the very least .250 to the crank from the rear face of the bushing.
[This message has been edited by 84Bill (edited 11-18-2008).]
IIRC, its a round washer like with holes in it for the bolts to go through, its about 1/16th of an inch thick. Ive seen a lot of them on automatics. It would do nothing but extend the flywheel\flexplate from the engine, I assume it has to do with seating depth of the input shaft splines, auto or manual.
Ahh.. and here we are. Googling that part number and "flywheel" produces
Check out page 13, part #36 It clearly illustrates this "washer" I describe Page 14 refrences it as "Spacer gear to C shaft"
Also, the illustration shows that it is only used with an automatic flexplate. It could also allign the ring gear to the starter, that or the input splines to the torque converter, I dont know which.
[This message has been edited by 86GT3.4DOHC (edited 11-18-2008).]
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05:02 PM
86GT3.4DOHC Member
Posts: 10007 From: Marion Ohio Registered: Apr 2004
AHAH! And you will also notice, the "crankshaft insert" Is a seperate entity to the "Pilot bushing"
THAT is why the clutch kits come with a "insert" Its not the pilot bushing, explaining why the Firebird kit came with 2 inserts, and the crankshaft has 2 seperate sized bores. There is absolutely no pilot bushing in the Fiero. There may well be a "insert" Which, is probably used to allign the torque converter, since IIRC, it has a nub on the back, it is very heavy, and very, very hard to line up, even with the engine on a stand. On a manual Fiero, it would be used to cradle the clutch allignment tool. Nether of those applications would be critical, and lack of the "insert" therefore would have no detremental effects.
The true pilot bushing, seats in the deeper crankshaft bore, far from the input shaft, and I still maintain that the flywheel ID is way to large to utilize the "insert"
[This message has been edited by 86GT3.4DOHC (edited 11-18-2008).]
Then there has to be a 1/4 inch spacer between the bushing and the flywheel.... The MUST be more than just 6 bolts to keep the flywheel on center and if there isnt then something needs to keep the input shaft from slapping around between the pressure plate and the flywheel.
Like I said in another post I had to be careful when putting the PP onto the flywheel to ensure they were lined up. I suspect this is to maintain balance.
Well here's my theory as to why 84Bill's '84 Duke had a pilot bushing installed. When Pontiac started building the '84 model Fiero, GM likely had many Dukes already built and set up for FWD applications. Instead of paying workers to remove a bushing that does no harm anyway, they just left it in. Is it possible that over the years, 84Bill's pilot bushing walked out of the crankshaft? From his description, it sounds like it did. I suppose that could happen since the bushing just press fits into the crank and the transaxle input shaft wasn't inside the bushing. Also, I haven't seen anyone in either thread claim their '85 or up Duke had that bushing. That's my theory and if someone can show me where I'm wrong, that's ok too.
Not trying to flame anybody, just trying to learn and help when I can. After all, that's what this forum is all about.
Mike
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05:20 PM
86GT3.4DOHC Member
Posts: 10007 From: Marion Ohio Registered: Apr 2004
something needs to keep the input shaft from slapping around between the pressure plate and the flywheel.
There are two VERY strong bearings inside the transmission, one on the far end, and one just behind the bellhousing end. These maintain the input shaft in a paralell path with the second gear shaft, and therefore, the splined section of the input shaft perpendicular to the bellhousing. This has been brought up many, many times. These bearings not only absorb the minimal force on the clutch disk forcing it out of line, but they support the entire force of the internal gears trying to shove the two shafts apart as they spin. If the bearings were loose enough to allow the input shaft to wobble that much, the gears would blow apart first.
" The MUST be more than just 6 bolts to keep the flywheel on center and if there isnt then something needs to keep the input shaft from slapping around between the pressure plate and the flywheel."
This has been adequately explained here more times than I care to count. Your intelligence is suspect.
Originally posted by 86GT3.4DOHC: If the bearings were loose enough to allow the input shaft to wobble that much, the gears would blow apart first.
Well something caused my flywheel to part company and I suspect everything and discount nothing, not even what the so called experts say. It's not like my trans was "abused" as many like to say. I maintain my engine and trans and regularly changed the oil in both.
If the tip of the input shaft is close enough to the pilot bushing... just enough to enter it by .050, it would have been enough to arrest the wobble and keep this disk centered... JUST enough... And that's WAY better than nothing at all.
Damnit... How many times do I need to say this... it's not an 84 duke, it's an 88 2.5 151 cid
Not being nasty to you rather I'm trying to clear things up a bit.
Seems there lost of people with illconceived and preconceived notions that need to be dispelled.
Well sorry about that but with trying to keep up with 2 threads it's getting difficult to keep track of everything. Ok, so much for that theory............. next!
Mike
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05:33 PM
GT86 Member
Posts: 5203 From: Glendale, AZ Registered: Mar 2003
Well something caused my flywheel to part company and I suspect everything and discount nothing, not even what the so called experts say. It's not like my trans was "abused" as many like to say. I maintain my engine and trans and regularly changed the oil in both.
If the tip of the input shaft is close enough to the pilot bushing... just enough to enter it by .050, it would have been enough to arrest the wobble and keep this disk centered... JUST enough... And that's WAY better than nothing at all.
The most probable cause is that your bolts failed. What grade did you use, and what did you torque them to? Your bolts could also have begun backing out, which eventually will cause them to start coming in contact with the disc. At that point, it's only a matter of time before the heads are sheared off and you lose the flywheel.
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05:39 PM
86GT3.4DOHC Member
Posts: 10007 From: Marion Ohio Registered: Apr 2004
If the tip of the input shaft is close enough to the pilot bushing... just enough to enter it by .050, it would have been enough to arrest the wobble and keep this disk centered... JUST enough... And that's WAY better than nothing at all.
Im not one to repeat what I say over and over again, but ....
Look at the pictures, for the shaft to go into the bushing, it would have to be .55" The shaft is much closer to 1" OD. You couldnt mate the two with a sledgehammer.
[This message has been edited by 86GT3.4DOHC (edited 11-18-2008).]
How about we get some more pictures of the actual failed parts? I've only seen one, an edge shot that doesn't really show much. We need front and back face shots of the flywheel, the clutch disk including closeups of the splined hole, the pressure plate including face and back at each bolt hole, trans input shaft tip and base where the input shaft housing attaches to the trans, and back of the crank flange. The pilot bushing issue is dead, about the only thing left to do is do a real failure analysis on the parts that actually were involved in the failure.
The most probable cause is that your bolts failed. What grade did you use, and what did you torque them to? Your bolts could also have begun backing out, which eventually will cause them to start coming in contact with the disc. At that point, it's only a matter of time before the heads are sheared off and you lose the flywheel.
That's what I believe too, for whatever reason the flywheel bolts failed.
