CherokeeHoonigan

So i have decided on boring and rebuilding my engine with a .020 bore. My questions:
1.) kit runs me 430$ total, my engine has not been bored yet so what are some ideas on shop fees? i know this veries on location and i am planning on going out looking at different shops near me just want to know what to look for on good deal wise.

2.) Do i have to bore the crank when i do the cylinders and bearings?

3.) How reliable is the engine after a bore like this? its the smallest bore i could do so i figured it is the best option, im not looking for insane power basically functionality, i could also get the regular rebuild kit and totally avoid a bore would this be a better option, or what this be a variable on what condition my engines in?

Thanks for reading and for any replies, happy building friends!

Kyle Morrison

i have a bored over remanned .020 as well and would like a motor head to chime in perhaps?

Is .020 too small for an increase in power?

dave1123

PERSONNALY, I doubt you'll see any difference in power over a standard bore size because you're only adding a couple of cubic inches. I refuse to do the math, but it can't be much more than that. I bored a 392 Hemi out .060" and only gained 13 cubes. Now if you STROKED it, you'd see something! Just remember that an overbore reduces the land between the cylinders and increases the chance of blowing the head gasket.

Why don't you measure the bores and see if you're within the wear limits to just put new rings in it. You don't have to line-bore the crank caps at all. Just have the crank checked for straightness. With 7 main bearings, I doubt there will be a problem with it. Also, measure the journals to see if you can get away with a set of standard bearing or if it needs to be ground undersize. Standard piston ring replacement sets usually have an expander spring that goes behind the first compression ring that helps the rings fit a worn bore.

Now I'm going with my experience with Chevy small blocks, but I think normal bearing clearances are .0005" to .0015" and a wear limit of .002". With the .002", you might want to install a high-volume oil pump. Not high pressure.

Remember for off-roading, you need torque, not horsepower. That's precisely what the 4.0 was designed for.

KaMoore

In addition to the above, overboring a 6 cylinder is not going to present quite the problems overboring a v 8 will. Something else most people don't do that I was taught to do is use a good assembly lube to coat all moving parts of the engine. I also plasti gauge the crankshaft journals and connecting rod bearings. I also will put a drill on the end of an old distributor shaft and pre prime the engine oil system just before the initial start. All this might be over the top, but I have never had an engine go bad that I rebuilt. The one time I had someone do it for me the engine used oil.

dave1123

Oh, most certainly Plastigage the bearings as you assemble it to make sure the running clearance is right. I don't spin up the oil pump, but I do crank the engine without ignition until oil pressure comes up before I light it off! On high stressed racing engines, we used an "accumulator" or tank of pressurized oil made from an old small fire extinguisher and a solenoid valve to supply pressurized oil to the bearings every time the key is turned on. Basically it just holds a quantity of oil under pressure when the engine shuts down to be used on start-up. Normally, most bearing wear is created before oil pressure comes up. Pressure is what makes the film the shaft rides on.

Fred/N0AZZ

He made no mention of mileage on that engine of cause of its demise that will tell what machine work will need to be done. That will have to be done by the shop it sounds like checking all clearances may be a bit beyond his skill set and tools required.


On a lot of engines a .020 overbore parts cost more that the std. .030 bore I don't know on the 4.0. How long you plan on keeping your Jeep will tell you what quality of parts you use and same for machine work.


A word of caution about cheap "Machine Shops" there is a reason for that one is usually skill level of operator and second is the age of the equipment some can be very worn out giving poor results of final work. I personally have saw some jobs that came from some of these shops and with a few they were junk when the customer got them back. I worked with B&W Racing Engines and Machine Shop for a few yrs was the sad part some of them were "race car engines" NOT.

CherokeeHoonigan

thread update: motor work will be beginning end of next month had a delay due to my builders shop burning down, i will try to take lots of pictures and i have a little supprise

Turbo X_J

I think you are going about this the wrong way.
In a nutshell:
First the engine is disassembled and cleaned then the various components & bore are measured. It may be determined that the bore is too far out of round that .020 won't be sufficient to clean it up and you may have to go .040 or .060. As long as the compression ratio remains unchanged you will never notice a difference. Measuring the crank if the mains and/or throws are worn excessively it will have to be turned down to a uniform size and oversized bearings installed. The high dollar guys actually fit the pistons to the bore and then if everything is kosher the ring end gaps are set....

TLDR
See what you got before you order any parts.
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ETA
"thread update: motor work will be beginning end of next month had a delay due to my builders shop burning down, i will try to take lots of pictures and i have a little supprise"

Hey look at the bright side at least they will have all new equipment (just make sure they know how to properly use it). Also try to make sure your stuff is first into the cleaning tank with the nice fresh soda solution.
While you've got some spare time, get this book & read it:
https://www.amazon.com/Engine-Repair...=1&*entries*=0

dave1123

Just an aside. Most vertical engines don't tend to wear out-of-round halfway near as much as a V or flat cylinder design, mostly because of gravity on the pistons. The last vertical engine that I saw that wore out-of-round was a farm tractor that ran for lots of years without an air filter and that one was tapered mostly. You can get a good indication by the wear ridge at the top of the piston travel.

Like Turbo xj says, you really won't know what you need until it's apart and measured up. I had a friend who ran G/Stock nationally with a 350 Camaro and when he built that motor, he bought a CASE of pistons to get 8 that were EXACTLY the same size and weight. He even bought 6 sets of lifters to get 16 the same. IDK how many connecting rods he had to buy for the same reason. NOTHING was left to cause a failure on a grudge-match teardown. Fred NOAZZ, this was the Baker&Evans G/Stock Camaro in the early 70's. He was torn down at Englishtown and the judges complained all the lifters were the same weight, suspecting they were modified. He had receipts to prove he bought all of them at dealerships. This is the length some guys will go to build a motor. WAY too rich for me!

CherokeeHoonigan

I will not be building the motor myself BUT i will be there assisting and overlooking the build, i have a few things i need to finish up including rear locker installation and we will be tearing the motor out and getting this done. thanks for the input and i will keep it in mind for my next motor build, all a learning process for me and i have to thank you guys for sharing your input and knowledge! Happy building brothers!