Bmann412's AMC 304 Rebuild - JeepForum.com
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post #1 of 117 Old 03-11-2020, 08:39 PM Thread Starter
Bmann412
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Bmann412's AMC 304 Rebuild

Being the first time I have ever rebuilt an engine I decided that it would be helpful for me and hopefully others to document my rebuild. Some background on the project, the engine came out of my 1978 Jeep CJ7 that I am in the process of rebuilding. More on the Jeep itself can be found here.

Now lets get this thread started!

Here is the motor in all of its glory, according to the odometer it has 40k miles and from the research and speaking with 2 of the previous owners it appears to be actual miles. unfortunately they were hard miles and the Jeep was road hard and put away wet.

img_0833.jpg

img_3543.jpg


1998 TJ 5.9l
1978 CJ7 Renegade
2013 JK
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post #2 of 117 Old 03-11-2020, 08:42 PM Thread Starter
Bmann412
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Engine Disassembly

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1998 TJ 5.9l
1978 CJ7 Renegade
2013 JK
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post #3 of 117 Old 03-11-2020, 08:44 PM Thread Starter
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Clean-up and Paint

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post #4 of 117 Old 03-11-2020, 08:45 PM Thread Starter
Bmann412
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Crankshaft Install

I began mocking up the Crankshaft after cleaning and installing all of the main bearings into the block. Just a note the main cap labeled #3 is the thrust bearing numbers 1,2,4,5 all use the same size bearing.

img_0311.jpgimg_0312.jpgimg_0313.jpg

With all the bearings in place I gently set the crankshaft into place. Once the crank was resting in place green plastigauge was cut into small strips and placed on the crank. The bearing caps were then all installed and torqued to 100 foot pounds as specified in the Factory service manual. The results were all a hair bigger the .002 but to small to be .0015 which should put us in spec according to the factory service manual, " Correct clearance is 0.0017 to 0.0020 inch (0.043 mm to 0.051 mm) on No. 1 through No. 4 main bearings and 0.0025 to 0.003 inch (0.064 mm to 0.076 mm) for the rear main bearing". The only issue I am seeing is the rear main bearing appears to not fall into spec. Being a novice I am not sure how to proceed. Should I take the crankshaft back to the machine shop to have it reground or can different bearings be used to get it into spec or am I over thinking things. Any advice would be greatly appreciated. I will be calling the machine shop to get there option.



img_0314.jpg img_0316.jpg

Main Bearing # 1
main1.jpg
Main Bearing # 2
main2.jpg
Main Bearing # 3 (thrust Bearing)
main3.jpg
Main Bearing # 4
main4.jpg
Main Bearing # 5 ( Rear Main)
main5.jpg

1998 TJ 5.9l
1978 CJ7 Renegade
2013 JK
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post #5 of 117 Old 03-12-2020, 07:01 AM
Matt1981CJ7
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Since your rear main is slightly tighter than spec, I wouldn't worry about it.

Matt


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post #6 of 117 Old 03-12-2020, 07:11 AM Thread Starter
Bmann412
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Quote:
Originally Posted by Matt1981CJ7 View Post
Since your rear main is slightly tighter than spec, I wouldn't worry about it.



Matt


I had a feeling that I was over reacting but would rather be safe then sorry. I am assuming it is better to have it on the tighter side but at what point would being to tight become a concern?

1998 TJ 5.9l
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post #7 of 117 Old 03-12-2020, 09:22 AM
Matt1981CJ7
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Considering NASCAR engines run at .001, or less, I think you're safe. Slightly tight is better than loose.

You could run a lower viscosity oil for the initial startup and break-in period, which is recommended anyway. That should eliminate any concerns.

Matt


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post #8 of 117 Old 03-12-2020, 10:02 PM
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There is a reason the rear main clearance is more than the others
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post #9 of 117 Old 03-13-2020, 06:44 AM
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I don't think anyone has ever spun a bearing because it was a half-a-thou too loose. Too tight though...

If it were mine, I'd swap the lower shell (maybe both) from the loosest cap to #5 and see if you can get your clearance right. I'm having a hard time telling where that is from the pics, though.

I'm assuming that AMC uses 4 of the same size bearings plus a thrust. I also don't know if you'll be able to get anywhere using plasti-gage. It'll probably take some Mr. Gadget eyeballs.


Shawn

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post #10 of 117 Old 03-13-2020, 07:26 AM Thread Starter
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After calling my machinist he didnít seem too concerned about it. He said they are well within spec from the bearing manufacturer. If I had to guess number 4 is the loosest bearing. Maybe I will swap then around and check it again.

1998 TJ 5.9l
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post #11 of 117 Old 03-13-2020, 08:23 AM
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Plastigauge is not a precise way of measuring your bearing clearance. Period. Plastigauge works well for the home builder, to get that good gut feeling all is right. Iím not knocking it, Iím just saying it has its place. You have used plastigauge to confirm your clearances are not out of the ballpark, and consistent. I wouldnít hesitate in running what you have there.
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post #12 of 117 Old 03-13-2020, 08:21 PM Thread Starter
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I decided to take your guys advice and run the crankshaft how it is. I re-cleaned the crank and bearings and applied assembly lube to each. I also installed the rear main seal and torqued everything to spec. The crank spins nice and smooth. Next up will be checking rod clearance. Which I will try and tackle this weekend.


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post #13 of 117 Old 03-14-2020, 07:19 AM
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Quote:
Originally Posted by Bmann412 View Post
I decided to take your guys advice and run the crankshaft how it is. I re-cleaned the crank and bearings and applied assembly lube to each. I also installed the rear main seal and torqued everything to spec. The crank spins nice and smooth. Next up will be checking rod clearance. Which I will try and tackle this weekend.

I don't see you having any problems with the mains and I'm sure your rods will be fine too. Looks good and I'm ready to see it run. You should post a video of the first start. Hopefully I'll be going through my 258 this summer so this is encouragement for me to read.
Shawn

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post #14 of 117 Old 03-14-2020, 09:54 AM
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Ben if you have ever had any conversations with mechanics over the way these generic crate engines are put together your mind will be at ease. As long as the bearings all get pre lubed you won't ever know the difference on that somewhat closer fit. It takes a while to do but priming the oil pump before you try to start the engine is time well spent. Not doing that could cause more damage than a close fitting bearing.
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post #15 of 117 Old 03-14-2020, 07:52 PM Thread Starter
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Quote:
Originally Posted by Jim1611 View Post
Ben if you have ever had any conversations with mechanics over the way these generic crate engines are put together your mind will be at ease. As long as the bearings all get pre lubed you won't ever know the difference on that somewhat closer fit. It takes a while to do but priming the oil pump before you try to start the engine is time well spent. Not doing that could cause more damage than a close fitting bearing.

Jim, that definitely makes me feel a lot better. All these shows on tv make this stuff look like rocket science and the tiniest thing will cause it to self destruct. I have been trying to keep everything as clean as possible and coating all bearings with a liberal amount of pre-lube.

Quote:
Originally Posted by kd7oir View Post
I don't see you having any problems with the mains and I'm sure your rods will be fine too. Looks good and I'm ready to see it run. You should post a video of the first start. Hopefully I'll be going through my 258 this summer so this is encouragement for me to read.
Shawn

Thanks Shawn, I am excited to get it all put back together. I am shooting to have the Jeep on the road by June for the Bantam Jeep Festival but we will see. I will for sure post a video of the first start up.

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