Replace crankshaft in vehicle? Possible to fit - JeepForum.com
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post #1 of 11 Old 05-13-2021, 08:58 AM Thread Starter
82/84 CJ7
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Replace crankshaft in vehicle? Possible to fit

Hello all, I hope all is well for everyone. I’m just asking a technical question for you all today, when I was rebuilding my engine the first time I had a extremely tight budget and very little time. Both of which forced me to make a hard decision. I re used my crnkshaft that was pretty worn.

I did have it polished but it still is grooved pretty good. Engine works fine. But when it gets up to operating temp my oil pressure goes from 40 lbs at idle to barley above 10. And I know exactly what it is. It’s the clearance on the main bearings is to big so when the oil thins out so does the pressure.

How hard would it be to replace the crank with the motor in the vehicle. Drop the pan. Maybe the front driveshaft. Pull the bearings and drop the crank?

Thank you
Jarod


84 CJ7 with 258 and T5 On 30x9.50x15 general grabber ATX
She ain’t fast but she’s fun.
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post #2 of 11 Old 05-13-2021, 09:12 AM
mystert29
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Ive changed the rear main seal, oil pan gasket, and timing cover w/gasket with the engine in the jeep. Ive seen BMW get rod bearings installed with the engine in the car. You should be able to do it but it might be pretty challenging. The length and weight of the crank will make it difficult to maneuver and you would have to hold it in place while you line up the caps. Lining up the big end of the rods will be difficult and theres a good chance you might nick the the journals. Also you cant reach down the cylinder to push the pistons up and down in the bores to line up to the rod journals on the crank. If it were me I would pull the motor.
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post #3 of 11 Old 05-13-2021, 09:47 AM
Fourtrail
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Not sure how you plan to pull the flywheel/clutch with the trans still attached, so I would think it would be easier to pull the motor than to try and pull the trans/tcase out so you can pull the clutch/flywheel to get the crank out. Plus with the plate between the engine and the bellhousing, you can't drop the crank straight down to get it out. Also, you oil pressure issue could be related to the cam bearings, so I would do those also when the engine is out if they weren't done the first time.

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post #4 of 11 Old 05-13-2021, 10:26 AM
mudbfun
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At the very least you will have to move the engine forward just to clear the transmission shaft. At that point you might as well pull the engine and do it right.

10 psi oil is a doomed motor. It will need to be addressed eventually.
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post #5 of 11 Old 05-13-2021, 10:45 AM Thread Starter
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Originally Posted by Fourtrail View Post
Not sure how you plan to pull the flywheel/clutch with the trans still attached, so I would think it would be easier to pull the motor than to try and pull the trans/tcase out so you can pull the clutch/flywheel to get the crank out. Plus with the plate between the engine and the bellhousing, you can't drop the crank straight down to get it out. Also, you oil pressure issue could be related to the cam bearings, so I would do those also when the engine is out if they weren't done the first time.
Honestly your completely right I don’t know how I forgot about the trans. And as for the cam bearings I’ll check but I think there good. I knew when I was reassembling this motor the clearance in the mains was quite high but everything else in the block was good. It was that scored crank. And the machine shop I took it too said they wouldn’t be able to turn the crank down for 3 months and I was not misled but a little over promised it wouldn’t affect it that bad.


And as for the 10-15 PSI hot idle. I don’t think the motor is doomed. I’ve personally driven jeep 258s that have made no more than 8-10 pounds at idle and maybe 30 under rpm that have been that way since I was born and they still drive fine. I don’t think the motor is invincible or anything but as long as I don’t beat it up super hard and keep up on maintenance.

It is always meeting the at least 10 PSI per 1,000 rpm rule of thumb and I never have any lifter noise or knocking. My goal when I assembled it was for the engine to hold for about 2-3 years while I get money and work and move and then when I have time and funds rebuild it properly and upgrade it a little. These motors are tough I have faith it’ll survive. It makes what like 112 HP only lol. Good on torque though.

84 CJ7 with 258 and T5 On 30x9.50x15 general grabber ATX
She ain’t fast but she’s fun.
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post #6 of 11 Old 05-13-2021, 03:30 PM
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It is always meeting the at least 10 PSI per 1,000 rpm rule of thumb and I never have any lifter noise or knocking.
If that’s the case why are you worried about? What oil are you running? Thicker oil will give you more pressure, but it sounds like it’s OK the way it is, right?

My 258 that I recently removed was about the same, except I believe mine was an original untouched “old worn out” 258.

If you think you are making 112 HP with an “old worn out” 258, you better fly the C-130 higher before you drop it out if it...LOL

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post #7 of 11 Old 05-14-2021, 12:49 PM
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What weight oil are you using?
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post #8 of 11 Old 05-14-2021, 06:20 PM
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Originally Posted by 82/84 CJ7 View Post
I did have it polished but it still is grooved pretty good. Engine works fine. But when it gets up to operating temp my oil pressure goes from 40 lbs at idle to barley above 10. And I know exactly what it is. It’s the clearance on the main bearings is to big so when the oil thins out so does the pressure.

Thank you
Jarod
10PSI at Idle? I know a lot of guys who would be happy with that.

Drive it. I bet you get plenty of mileage out of it.

No need to worry until it drops below 5 PSI at idle.....then you just go to a heavier oil.


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post #9 of 11 Old 05-15-2021, 11:53 AM Thread Starter
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What weight oil are you using?
Sorry I just saw this now, I’m using 15-40 rotella T5 oil with zinc additives. Works pretty good really. Besides the rear main leak because the scored crank engine is good. Compression is solid in every cylinder and it fires up within the first spin or two if the carb isn’t hot.

If only I could tune my Weber 38/38 better I’m sure there’s more performance out of her compared to our other 4.2 with a 32/36


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Quote:
Originally Posted by 82/84 CJ7 View Post
I did have it polished but it still is grooved pretty good. Engine works fine. But when it gets up to operating temp my oil pressure goes from 40 lbs at idle to barley above 10. And I know exactly what it is. It’s the clearance on the main bearings is to big so when the oil thins out so does the pressure.

Thank you
Jarod
10PSI at Idle? I know a lot of guys who would be happy with that.

Drive it. I bet you get plenty of mileage out of it.

No need to worry until it drops below 5 PSI at idle.....then you just go to a heavier oil.
Lol thank you that’s kinda what I’m thinking now. It doesn’t make any bad sounds but getting off the freeway and letting idle watching that pressure gauge go to 10 just still makes me uneasy sometimes but she’ll keep on running.

Friend of mines old 4.2 made maybe 8lbs at idle and never went above 20-25 under rpm. He had it for as long as I could remember driving it daily off road and highway before he rebuilt it for other reasons. There not powerful motors but the simple tractor engine doesn’t quit lol.

84 CJ7 with 258 and T5 On 30x9.50x15 general grabber ATX
She ain’t fast but she’s fun.
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post #10 of 11 Old 05-15-2021, 11:55 AM Thread Starter
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My engine when I first bought it was running in 3/6 cylinders and making maybe 20 lbs of pressure and barley 8-9 at idle. The jeep wouldn’t go over 45 but she never quit either. I found out when I pulled the valve cover the previous owner let sand get in the motor and it wasted the bearings and the oil pump. So my pressure was so low my lifters would collapse and my pushrods kept falling out of position.

That’s what made me do a quick garage rebuild the first time.

84 CJ7 with 258 and T5 On 30x9.50x15 general grabber ATX
She ain’t fast but she’s fun.
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post #11 of 11 Old 05-15-2021, 11:30 PM
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Quote:
Originally Posted by 82/84 CJ7 View Post


And as for the 10-15 PSI hot idle. I don’t think the motor is doomed. .

I misunderstood. Your first post made me think it dropped to 10 psi MAX after warming up. What is your oil pressure at cruising speed?
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