Tight Bearing Clearances?

[DanielB23]

So I haven't made a post in awhile but I've finally found a little more free time and began reassembly of my 5.0 v8. Because this is my first engine rebuild, there is all kinds of studying and learning I'm doing along the way. No rush on this project. I am encountering an issue with my main bearing clearances now and hoping someone here can help. This may be a long read, my apologies in advance.

Engine builder installed the cam bearings for me, I don't have measurements for those.

I installed my new camshaft (mild performance cam from Comp Cams) and I am using red Permatex ultra slick assembly lube. When I first installed my camshaft I used Permatex on the bearing surfaces and thick gray cam/lifter assembly lube on the lobes. When I had the camshaft in place I noticed resistance when spinning the cam by hand. Everything else I have seen, the camshaft spins very freely and easily. Mine took a good bit of force to turn but I never felt any binding or grinding. I suspect the assembly lube was just too thick? I pulled the cam out and cleaned it. This time using some oil (5W-20) on the bearings and Permatex on the lobes. Once the camshaft was in place this time, I was able spin it very easily. I thought to myself, ok awesome let's move on.

Got around to the crankshaft install. I used green plastigage to measure bearing clearance but I only measured the number 1 main cap (Yes, stupid. A YouTube video mislead me to believe that's all I needed to measure). The plastigage measured at .0015. So I continued with my crank install and used Permatex on the bearings. Once I had the crank installed and torqued down, I encountered the same resistance that I did with the camshaft. No binding/grinding, just an abnormal amount of force to rotate the crankshaft by hand. This is where I have left off and decided It's time to pause and ask some questions.

I've read that plastigage is just fine for these measurements and I've also read that you need a micrometer and dial bore gauge. I'd like to get by with plastigage if possible.

I ordered another strip of plastigage because when I broke off my first piece I just pulled it, causing the plastigage to stretch. Possibly throwing off my measurements?
I read that assembly lube is better instead of using oil especially if your engine will be sitting for awhile. That oil can run whereas the assembly lube will stay in place. But I've also heard you can just prime the engine prior to first startup which would ensure oil is in all the places it should be?

In my Haynes manual, the main bearing journal specs suggest bearing oil clearance to be .0008 to .0015 inch. I've had someone tell me .0015 is pushing the tight side and .0020-.0025 is more where you want to be. Can anyone provide some insight on this?

Thank you, I know this was a long. If you actually read this far it means a lot to me

 

[DanielB23]

So I haven't made a post in awhile but I've finally found a little more free time and began reassembly of my 5.0 v8. Because this is my first engine rebuild, there is all kinds of studying and learning I'm doing along the way. No rush on this project. I am encountering an issue with my main bearing clearances now and hoping someone here can help. This may be a long read, my apologies in advance.

Engine builder installed the cam bearings for me, I don't have measurements for those.

I installed my new camshaft (mild performance cam from Comp Cams) and I am using red Permatex ultra slick assembly lube. When I first installed my camshaft I used Permatex on the bearing surfaces and thick gray cam/lifter assembly lube on the lobes. When I had the camshaft in place I noticed resistance when spinning the cam by hand. Everything else I have seen, the camshaft spins very freely and easily. Mine took a good bit of force to turn but I never felt any binding or grinding. I suspect the assembly lube was just too thick? I pulled the cam out and cleaned it. This time using some oil (5W-20) on the bearings and Permatex on the lobes. Once the camshaft was in place this time, I was able spin it very easily. I thought to myself, ok awesome let's move on.

Got around to the crankshaft install. I used green plastigage to measure bearing clearance but I only measured the number 1 main cap (Yes, stupid. A YouTube video mislead me to believe that's all I needed to measure). The plastigage measured at .0015. So I continued with my crank install and used Permatex on the bearings. Once I had the crank installed and torqued down, I encountered the same resistance that I did with the camshaft. No binding/grinding, just an abnormal amount of force to rotate the crankshaft by hand. This is where I have left off and decided It's time to pause and ask some questions.

I've read that plastigage is just fine for these measurements and I've also read that you need a micrometer and dial bore gauge. I'd like to get by with plastigage if possible.

I ordered another strip of plastigage because when I broke off my first piece I just pulled it, causing the plastigage to stretch. Possibly throwing off my measurements?
I read that assembly lube is better instead of using oil especially if your engine will be sitting for awhile. That oil can run whereas the assembly lube will stay in place. But I've also heard you can just prime the engine prior to first startup which would ensure oil is in all the places it should be?

In my Haynes manual, the main bearing journal specs suggest bearing oil clearance to be .0008 to .0015 inch. I've had someone tell me .0015 is pushing the tight side and .0020-.0025 is more where you want to be. Can anyone provide some insight on this?

Thank you, I know this was a long. If you actually read this far it means a lot to me

Also, I will be going back to pull the crankshaft and measure those clearances with plastigage. I'm just at a point where I've become confused and unsure about the correct measurement and how to accurately get the measurement

 

[dvdswan]

Depends on the year of the engine I would imagine. This says 0.0015 to 0.0020

Google Search

 

[CDW6212R]

For a perfectly machined engine, the crank and main bearing journals, those can do fine with 1.5 thousands of clearance in normal applications. That applies to 99% of engine builds, racing or much higher rpm engines need more clearance, and those have to spend more time and thought on oil pressure and volume.

For a normal build, you can do fine without proper bore gauges. But you really much be sure of what the clearances are, that is trust well enough to proceed. Use the plastigage on all main journals, mainly that is checking on the machine work quality. The results will probably vary a lot, so watch out for results that are .001 or less, as well as .025 or more. I'd aim for .0015-.0025, many people shoot for .002 and no more. Rod journals are similar but the rpm band and power affects the choice more. What you want to find is no odd low or high clearances, but numbers near the goals. Then you can feel comfortable in assembling the engine. Use oil for test fitting and the clearances, then assembly oil(especially on cam and lifters etc) for the final task.

Enjoy the build, go slow and enjoy it.

 

[410Fortune]

@CDW6212R He has you covered

The camshaft needs the assembly lube more then the crank simply because the crank sits down in the oil and like you said you are going to prime the engine before startup
So it’s ok to use oil on crank

Sounds like you are doing a good job thus far! I’ve watched about 300991 hours of vice grip garage so I’m really familiar with the process you are going through now. Derek Biari does a fine job of explaining budget engine builds and valve train geometry engine assembly for the backyard mechanic in his videos

Way to tackle an engine rebuild! Good job

 

[DanielB23]

For a perfectly machined engine, the crank and main bearing journals, those can do fine with 1.5 thousands of clearance in normal applications. That applies to 99% of engine builds, racing or much higher rpm engines need more clearance, and those have to spend more time and thought on oil pressure and volume.

For a normal build, you can do fine without proper bore gauges. But you really much be sure of what the clearances are, that is trust well enough to proceed. Use the plastigage on all main journals, mainly that is checking on the machine work quality. The results will probably vary a lot, so watch out for results that are .001 or less, as well as .025 or more. I'd aim for .0015-.0025, many people shoot for .002 and no more. Rod journals are similar but the rpm band and power affects the choice more. What you want to find is no odd low or high clearances, but numbers near the goals. Then you can feel comfortable in assembling the engine. Use oil for test fitting and the clearances, then assembly oil(especially on cam and lifters etc) for the final task.

Enjoy the build, go slow and enjoy it.

Great information, thank you!

 

[DanielB23]

@CDW6212R He has you covered

The camshaft needs the assembly lube more then the crank simply because the crank sits down in the oil and like you said you are going to prime the engine before startup
So it’s ok to use oil on crank

Sounds like you are doing a good job thus far! I’ve watched about 300991 hours of vice grip garage so I’m really familiar with the process you are going through now. Derek Biari does a fine job of explaining budget engine builds and valve train geometry engine assembly for the backyard mechanic in his videos

Way to tackle an engine rebuild! Good job

Thanks man! I'll have to check his videos out.

 

[DanielB23]

For a perfectly machined engine, the crank and main bearing journals, those can do fine with 1.5 thousands of clearance in normal applications. That applies to 99% of engine builds, racing or much higher rpm engines need more clearance, and those have to spend more time and thought on oil pressure and volume.

For a normal build, you can do fine without proper bore gauges. But you really much be sure of what the clearances are, that is trust well enough to proceed. Use the plastigage on all main journals, mainly that is checking on the machine work quality. The results will probably vary a lot, so watch out for results that are .001 or less, as well as .025 or more. I'd aim for .0015-.0025, many people shoot for .002 and no more. Rod journals are similar but the rpm band and power affects the choice more. What you want to find is no odd low or high clearances, but numbers near the goals. Then you can feel comfortable in assembling the engine. Use oil for test fitting and the clearances, then assembly oil(especially on cam and lifters etc) for the final task.

Enjoy the build, go slow and enjoy it.

I made an additional post on this issue, meant to just add onto this thread but oh well. Here are the plastigage measurements I got yesterday.
Cap 1: .0014 - .0015
Cap 2: .0014 - .0015
Cap 3: .0015 - .002
Cap 4: .0014 - .0015
Cap 5: .0015 - .002

I plan on reinstalling the crank just using some 5W-20 oil on the bearings and seeing how it feels/spins. If it's good, I was going to take it out and clean it one last time and reinstall with assembly lube (expecting more resistance when spinning it).

 

[CDW6212R]

The force to spin the crank freely with oil and the rods/pistons is often around 35lb/ft or less.

 

[410Fortune]

So much knowledge on this forum!

I’m going down this path soon renaming a good running 302 with all new everything