258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

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backroader
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258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by backroader »

Thinking of rebuilding the 258 I6 with Chrysler 727 auto in my 81 J10...

The engine has good oil pressure (about 60# at cold startup), but drops to under 10# at warm idle. I have already replaced main & rod bearings and checked clearances with Plastigage, and they are all within specs, but some do have some minor scoring on them. The local machine shop quoted $225 to regrind the crank to .010 under.

I have another older 258 engine with what I believe is a good crank that is mated to a GM/Borg Warner automatic. I was told by the previous owner that the engine only has about 50K since rebuild, but he suspected a cracked head or bad head gasket, since it was apparently getting coolant into one of the cylinders when it was running. I have pulled the head off that engine, and see no signs of this in the cylinders, gasket, or the head. I have not had the head or the block magnifluxed, however. The block casting number on this engine is 3227445 with a date code of 208C18, so I believe this engine is a replacement, being the engine is presently residing in a 71 Wagoneer. I have also pulled the oil pan, and checked the main & rod journals, and they look like new, with absolutely no visible wear to the journals or bearings..

So I'm thinking of using parts from both engines to rebuild the one that is currently in my J10. One of the questions/issues I see that may be a problem is in mating the crank flange from the (older) Waggie engine to the torque converter/flex plate in the J10.

From the research I've done, it appears there was some sort of adapter made to fit the Chrysler transmission to the older style crank flange, but the information I've found is sketchy and conflicting, so I thought I would see if anyone on here has run into this issue, or has more knowledge about it than me.

Looking for comments, suggestions on which route to take, or any ideas that might be useful..thanks.

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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by backroader »

Sorry about the double post...not a regular poster on this site.
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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by Stuka »

To my knowledge, the crank flange on all 258's are the same. The older version of the AMC i6 was different.

However, its worth noting the cranks are different. 79 and older have a much heavier crank. In 80, the crank was lightened. There are plenty of argument as to which one is better. The older one was more grunt, but the newer one revs faster and higher. But they can be swapped back and forth from what I know.

AMC was using both GM and Chrysler transmissions at the same time with the same engine in various vehicles. Jeeps used the TH400, but cars used the 904/727. Then in '80, then everything switch to 727/904.

Its also worth noting that AMC i6's do have lower idle oil pressure. Just the way they are. Mine was always in the 10-15psi range at warm idle. Drove it like that for 40K miles without any issues. They have a low idle RPM, and the pump just doesn't displace much oil at idle. Oil pressure at cruising speed is much more important.
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backroader
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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by backroader »

The engine that is presently in the truck holds between 30 & 40 pounds of pressure on the mechanical gauge when cruising. I have ran it this way for several thousand miles now as a daily driver. The engine doesn't consume much oil, and doesn't smoke, so maybe I should just run it this way???

It does show some condensation under the oil filler cap, so there must be some blow-by coming from somewhere.

I finally got the rear seal to stop leaking after two replacements...
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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by tgreese »

There was a transition crank pattern for the 258, and it's right at the 1971 model year as I recall. I would not assume that these cranks are compatible. In this 70-71-72 era, compatibility is really dicey.

I'm telling this story as I remember it - maybe later I can dig out the books later and try and confirm some dates and part numbers.

Prior to '72ish (?) AMC used the Borg-Warner M-series transmissions in their cars. I think the crank pattern on the previous 199/232 engines ("Rambler" OHV seven-main-bearing six) matches these B-W transmissions. AMC took the 232/199 and stroked and changed the deck height to make the "unified" 232 and 258. The bell pattern was changed to match the current AMC V8s. I recall there were 258s from 1970-71 that matched the B-W transmission and are different (and incompatible) with the later AMC sixes. Kinda think they changed to another crank design in '72-ish when they dropped the outmoded B-W automatics and switched to Chryco Torqueflights. AMC purchased these from Chrysler for their passenger cars as a commodity part, with a bell pattern that matched their engines.

Now, it gets worse - Jeep was committed to the GM TH400 in 1970. Each of their engines had been adapted to the TH400 using a ring adapter for the bell pattern and some combination of parts to adapt the crank pattern. Jeep stayed with the TH400 until 1980, continuing to adapt the TH400 to each engine revision.

Thus, if you look in the '62-73 Jeep factory parts book here https://oljeep.com/edge_parts_man.html you can follow the parts evolution. You will find an adapter for the Rambler 232, for the "transitional" 258, and for the "mature" 258. Maybe you can glean some info there.

JMO - you should put these engines side by side with the crank end exposed and compare.
Last edited by tgreese on Mon Apr 10, 2023 1:28 pm, edited 2 times in total.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by tgreese »

backroader wrote: Mon Apr 10, 2023 1:11 pm...
It does show some condensation under the oil filler cap, so there must be some blow-by coming from somewhere.

I finally got the rear seal to stop leaking after two replacements...
You can have good compression and low oil pressure, and vice-versa. It is possible to replace the rings after a ridge ream and hone. Cast iron rings only, no moly or chome (won't seat unless the bores are straight). The replacement rings won't last as long as in a new or over-bored block; the tapered bores fatigue the rings and they wear out sooner.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by backroader »

This one has the adapter ring between the GM transmission and the bell housing.

I suppose the only way of telling for sure is to pull both engines and look at the flange on the crank.

This all gets really confusing...

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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by backroader »

I should probably pull the head on the newer engine first, and see what I can see with the condition of the cylinders and head.
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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by tgreese »

backroader wrote: Mon Apr 10, 2023 1:33 pm This one has the adapter ring between the GM transmission and the bell housing.

I suppose the only way of telling for sure is to pull both engines and look at the flange on the crank.

This all gets really confusing...
All Jeeps from this era (1965-1974ish) with an automatic transmission will have an adapter ring. Each engine Jeep used has a different adapter ring. The AMC cars are different - they never used the GM transmission that Jeep did. However, I gather the passenger car development drove the engine design, and as part of AMC, Jeep was carried along.

In 1980, Jeep changed from the GM transmissions to the Torqueflite that's the same as the AMC cars.

It would not be a problem if the replacement engine were a few years newer. However, in that '70-71 transition era, you are likely to be surprised if you assume.

There may be a part number on the ring adapter. If so, it may be specific to the transition 258. That would be telling. Or maybe you can match up the casting numbers - there are online pages with some of this info as I recall. The crank casting number would tell you, but it's probably easier to pull the engines and compare the flanges.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
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backroader
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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by backroader »

Where is the casting number for the crank located? This might save me some work..
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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by tgreese »

I don't know specifically, but it would be on the crank. Minimum, you'd need to pull the oil pan to see it, I'd think.

This might be helpful - https://www.jeepstrokers.com/forum/viewtopic.php?t=51

Above thread has a lot of info, but a quick perusal does not reveal where on the crank the numbers are. Maybe it's obvious if the crank is in front of you.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by Stuka »

backroader wrote: Mon Apr 10, 2023 1:11 pm The engine that is presently in the truck holds between 30 & 40 pounds of pressure on the mechanical gauge when cruising. I have ran it this way for several thousand miles now as a daily driver. The engine doesn't consume much oil, and doesn't smoke, so maybe I should just run it this way???

It does show some condensation under the oil filler cap, so there must be some blow-by coming from somewhere.

I finally got the rear seal to stop leaking after two replacements...
The condensation under the filler cap is very normal for these engines if the vehicle doesn't get driven long distances. For a while I worked 2 miles from home, and it started to get really bad. Basically, its a lot of mass that takes a while to get hot enough to vaporize any water that gets in there. My fix was to take it on some expended drives on the weekends. When I switched to a job that was 12 miles away, the issue went away entirely.

And I had forgotten that there was some 258s with the old style crank. I had thought this was only for the 199/232. And that the 258 was the start of the change over. But tgreese is likely correct.
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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by tgreese »

I would also point out that, prior to 1972, AMC/Jeep did not include the year of manufacture in the VIN numbers. That 1971-registered Wagoneer could be a '70 that sat on the lot and was newly registered in 1971. We see this a lot with CJs - the year on the registration does not always conform to serial number registry.

Unlike 1972 and later, the sequential serial number part of the Jeep VIN was not reset with each new model year. You can more-or-less determine the date of manufacture by comparing the serial number to the registry. Some of this registry data (for CJs) came from old factory records that were saved by enthusiast, and some comes from reported serial numbers of owners.

If it's actually 1970 production, it could be a Rambler 232. I recall you can identify these by the starter located on the driver's side of the bell housing. '72-on are all on the passenger side. I think I encountered a claim that the '71 transition engine had the starter on the driver's side, but I'm not certain. There may be a picture in the parts book. The ring adapter has to change in '71 because the bell pattern went to the "unified" V8 pattern. (Apparently not - see below.) If there is a separate adapter for the '71, that would indicate the starter side changes in '72, not '71.

ringadapter.png

You can look at the book and find this illustration in group 1, though these parts are listed in group 6.

Only some applications used the crank adapter, 6.521-1. All used the ring adapter, 6.525-1.

6521dash1.png
6525dash1.png

This is surprising - I would have expected all 258s to use the same ring adapter, since that only depends on the block pattern, not the crank pattern. You can see that the crankshaft spacer only applies to the '72 and up, and is the same for all AMC engines, sixes and V8s. This implies that the bell pattern for the sixes did not change until 1972, and there were 1971 258s that had both the earlier "Rambler six" pattern and no crankshaft adapter. Huh.

(This also implies that the 232/TH400 combo was available in the bullnose Commando. Also huh. I have never seen one. The "unified" 232 was not offered in the Wagoneer or J-trucks; that's an error in the listings.)

If my time/effort were limited, I would trust the parts book and reject any six engine with the starter on the driver's side. Either it's a Rambler 232 ('70ish) or a transition 258 ('71ish). Both will have the wrong bell pattern for your Jeep.

Sorry for my geeking out on this, but that's how you learn. Pick a problem and try to solve it.
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Last edited by tgreese on Sat Feb 24, 2024 11:33 am, edited 1 time in total.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by backroader »

And I had forgotten that there was some 258s with the old style crank. I had thought this was only for the 199/232. And that the 258 was the start of the change over. But tgreese is likely correct.
From the information I've seen, the only difference (outside of the number of counterweights) was the early 258 crank had a 1/8" deep "step", or recess, in the center of the flange, where the later cranks were just flat. I can't really see where this would be a huge issue as long as the pilot bearing or hole was the right size.

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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by backroader »

I would also point out that, prior to 1972, AMC/Jeep did not include the year of manufacture in the VIN numbers. That 1971-registered Wagoneer could be a '70 that sat on the lot and was newly registered in 1971. We see this a lot with CJs - the year on the registration does not always conform to serial number registry.

Unlike 1972 and later, the sequential serial number part of the Jeep VIN was not reset with each new model year. You can more-or-less determine the date of manufacture by comparing the serial number to the registry. Some of this registry data (for CJs) came from old factory records that were saved by enthusiast, and some comes from reported serial numbers of owners.

If it's actually 1970 production, it could be a Rambler 232. I recall you can identify these by the starter located on the driver's side of the bell housing. '72-on are all on the passenger side. I think I encountered a claim that the '71 transition engine had the starter on the driver's side, but I'm not certain. There may be a picture in the parts book. The ring adapter has to change in '71 because the bell pattern went to the "unified" V8 pattern. (Apparently not - see below.) If there is a separate adapter for the '71, that would indicate the starter side changes in '72, not '71.
The only visible difference in the two engines I have (outside of the casting number & date code) is the engine in the Waggie has the 1/2" head bolts and bolt-on valve cover.

I would actually prefer to use the earlier engine if it checks out ok, and I can get around the crank fitment issue...

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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

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From the info I have, the 4th digit in the date code is the letter C, which confirms the engine is a 258.

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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by backroader »

Oh, I should mention I also have a 3rd 258 engine with a build date code of 304C11.

This was in a bare chassis from a 1977 J10 with a manual transmission sitting out in the open weather for years uncovered. I was surprised to learn that the engine wasn't locked up. I did a compression check on all 3 engines 2 or 3 years ago, and all three had decent readings, but the engine in the Waggie had the highest readings of the three.
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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by tgreese »

You may have tapped out the knowledge here related to this problem. Suggest you might ask on the AMC forum https://theamcforum.com/ about this issue. The JeepStrokers link above lists the '71 258 crank casting and part numbers but does not offer any warning about it not being compatible with with a 4.0L block (the focus of that site). They have a forum "swapology" where this question might be appropriate.

Note that you can search specific forums in your favorite search engine with search strings like "site:theAMCforum.com 1971 258 crankshaft".
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
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tgreese
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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by tgreese »

backroader wrote: Tue Apr 11, 2023 8:44 am I can't really see where this would be a huge issue as long as the pilot bearing or hole was the right size.
I understand your reasoning. However, it seems AMC changed the flange to be compatible with the Chrysler transmissions. This is the same transmission you want to pair this engine with. Could be that AMC eliminated the recess to make the machining of the cranks less expensive. That does not seem like a very strong reason. Maybe.

The 727 flex plate has to match the crank end. If the recess is inside the bolt circle of the 727 flex plate, you could maybe make a disk to fill the recess. The pilot tip diameter does not matter to an automatic. In some cases, the crank end supports the torque convertor, and then the recess diameter would need to be right. In this application, the TH400 needs an additional bushing to make this right. I would ask on the AMC forums.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
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Re: 258 I6 Borg Warner to Torqueflite 727 crankshaft compatibility

Post by tgreese »

Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
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