I am going to be installing my long awaited 4.2L into the 1990 RRC soon, but I have hit a snag. I can't buy a crankshaft harmonic balancer for a 4.2L. Can I use the 3.9L one or will that cause problems down the road?
crankshaft harmonic balancer
- Thread starter agbuckle98
- Start date
hard to say I just ran into a similar snag.
I was swapping a Vbelt engine into a serpentine truck
the serpentine crank shaft has a longer key way cut into it then the vbelt crank.
5min with a cut off wheel and I was back in business
I was swapping a Vbelt engine into a serpentine truck
the serpentine crank shaft has a longer key way cut into it then the vbelt crank.
5min with a cut off wheel and I was back in business
MUSKYMAN said:hard to say I just ran into a similar snag.
I was swapping a Vbelt engine into a serpentine truck
the serpentine crank shaft has a longer key way cut into it then the vbelt crank.
5min with a cut off wheel and I was back in business
i dont see it being a problem with the 3.9 one.....im using the 3.5 vbelt with my 4.6! Really you wont notice a difference
ptschram
Well-known member
The harmonic balancers should be interchangeable within engine groups, ie serpentine and non-serpentine. In Thom's case, a shorter woodruff key probably would have done the trick, but his method worked just as well, I'm sure.
FWIW-the harmonic balancers are available from RN, but I could think of much better ways to spend the several hundred dollars they want for one.
FWIW-the harmonic balancers are available from RN, but I could think of much better ways to spend the several hundred dollars they want for one.
ptschram said:
no sir
the shorter woodruf key and key way on the v belt crank would not have had any key way in the harmonic balencer of the serpentine style harmonic balencer/pulley.
so to get the key into the balencer I need to cut the keyway longer and use the longer key.
seems to work just fine.
yes I am old school
ALl of the balancers are available from RN except for the 4.2L. I have heard from other sources that using a 3.9 balancer on a 4.2L engine will result in a broken crankshaft. I know there are lots of people out there who have done 4.6 conversions and are most likely using their old 4.2 or 3.9 balancer with no issues, but this may be something thjat takes 10 - 15 K miles to surface.ptschram said:
I may have a 4.2 harmonic balancer. Let me check the shop tomorrow. I've taken apart several '93 LWB's this year.
a short bit of research has turned up that the same balancer is used for the RRC 3.9L from '87-'95. Could one safely assume that the 4.2L balancer would be the same for '93-'95? I realize the '95 engines are serpentine belt, and the earlier ones were V-belt, but all the pulleys just bolt to the damper.
this suprises me?
the front covers are different as the 94-95 has the crank mounted oil pump and the v-belt engines have a distributor shaft driven pump.
I am looking forward to learning more about this
the front covers are different as the 94-95 has the crank mounted oil pump and the v-belt engines have a distributor shaft driven pump.
I am looking forward to learning more about this
ptschram
Well-known member
agbuckle98 said:
No, the serpentine balancers for distributor engines are different from those for V-belts and those for distributor-less engines.
Thom:
I've read and re-read your posts and still don't understand what you did, nor why. I have put serpentine engines into vehicles that originally had V-belts and did not need to do any modifications other than to the fan shroud.
I sure hope my new 4.2 (if it ever gets built) doesn't explode from my using my 3.9 balancer on it
ptschram
Well-known member
ptschram said:
ok picture this.
the block I used came out of a 1994 defender. the crank only had a 1" key way cut into it and that keyway was cut so the only thing it would engage with was the oil pump drive gear once the serentine cover way slid into place.
so once the serentine front cover was installed with the oil pump drive gear in place the crank left exposed was just a bare round shaft with no key way. so then the harmonic balencer would not have anything holding it indexed to the shaft.
to remedy this I extended the key way on the sahft to the full length that the serpentine block had buy cutting the crank shaft and using the longer woodruff key from the serpentine engine. It was really a pretty easy fix and took me less time to do then it has to explain to you Paul:smilelol:
ptschram
Well-known member
Had you said that you were putting a serpentine balancer on a non-serpentine crankshaft, it would have been understood the first time around. Go back and read what you wrote, you'll understand my confusion.
You also have a good bit of the balancer unsupported as the crankshaft is quite a bit shorter. How long has this setup been running? I've been curious about the long-term implications of doing what you did. I bought a serpentine 4.2 crank to avoid having to worry about what you did.
PT
You also have a good bit of the balancer unsupported as the crankshaft is quite a bit shorter. How long has this setup been running? I've been curious about the long-term implications of doing what you did. I bought a serpentine 4.2 crank to avoid having to worry about what you did.
PT
ptschram said:
nope...cranks are exactly the same length...only difference was the length of keyway.
ptschram
Well-known member
MUSKYMAN said:
Er, are you sure of that? I have measured them as I was of the same opinion until I measured a couple of crankshafts and found those from serpentine engines are quite a bit longer.
I'll take some pics.
So are the GEMS and Bosch engine crankshafts even longer still? I was standing in the observation deck of a 4.2 - 4.6 conversion (didn't get to get my hands dirty) done on a '95 and the new crank was about an inch or so longer than the old '95 4.2 and required the use of a spacer over the nose of the exposed crankshaft so the bolt would tighten everything down. Are there then 3 different lengths of crankshaft to deal with?ptschram said:
ptschram
Well-known member
4.6 GEMS 3.5" from first journal to end of crankshaft
4.2 Lucas (serpentine) 2.75"
3.9 Lucas, (V-Belt) 2.75" short keyway
4.2 Lucas (V-belt) 2.75 short keyway
Goddamit! I'm wrong again!
OK, this is twice in the same day. I'm going to go hide in the shop and read and measure and observe and not say another freaking word until I can go back to being a right (er, correct) as Rush Limbaugh!
Apparently, I did not need to buy the serpentine crankshaft for my 4.2 project, I just needed to have the key way cut longer. Oh well, they both needed to be ground anyway so no big loss.
4.2 Lucas (serpentine) 2.75"
3.9 Lucas, (V-Belt) 2.75" short keyway
4.2 Lucas (V-belt) 2.75 short keyway
Goddamit! I'm wrong again!
OK, this is twice in the same day. I'm going to go hide in the shop and read and measure and observe and not say another freaking word until I can go back to being a right (er, correct) as Rush Limbaugh!
Apparently, I did not need to buy the serpentine crankshaft for my 4.2 project, I just needed to have the key way cut longer. Oh well, they both needed to be ground anyway so no big loss.