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Old 11-17-2010, 07:47 PM   #21
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He will already have the oil pan and head off to change out rods, pulling main caps isn't going to cause contamination worse than those two operations. The reason you'd do it is when you've taken the time, effort, and expense to take the engine apart that far you may as well do main bearings. This way you know for absolute fact you have good ones in place. Leaving the old ones in damn near guarantees someone didn't change the oil regularly in the past and the bearings look like *****.
At what point do you stop replacing things? At this point you could also replace piston rings, valve stem seals, etc etc. I've struggled in determining what I will be doing when I take my engine apart, but have to draw the line somewhere.
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Old 11-17-2010, 07:59 PM   #22
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At what point do you stop replacing things? At this point you could also replace piston rings, valve stem seals, etc etc. I've struggled in determining what I will be doing when I take my engine apart, but have to draw the line somewhere.
This was my big dilemma when building as well.

Everyone and their mother was telling me to replace EVERYTHING. Its a very slippery slope. You do rods, pistons, rings, bearings, studs, gaskets, valve seals, oil pump, water pump, timing belt, etc etc etc etc etc etc and it pretty much doesn't end til you've got a motor that is 99.9% rebuilt/replaced from the ground up. Not a bad thing but most can't afford that.

Definitely better safe then sorry and DEFINITELY a good idea to replace as many things as you can afford, but we own miata's not m5's, so a 5 thousand dollar engine build isn't in many people's budgets: you gotta draw the line somewhere.
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Old 11-17-2010, 09:58 PM   #23
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Get the small end measured as well. I had to hone mine a touch to fit FM Wisecos.
Omniman just used heat on the small end.
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Old 11-17-2010, 11:06 PM   #24
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+1 for balancing the rotating assembly if you are changing any rotating part it needs to be balancing, also if you dont change the rings you dont need to run a brake in oil, the bearings dont need to "break in". Are you going to check the cylinders to make sure that they are still perfectly round and not tapered? if they are out of round or tapered it would be good to change the pistons which would mean that it is time to bore the block as well. I dont know your goals for the car, but it sucks to do things over. You should do it right the first time.
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Old 11-17-2010, 11:59 PM   #25
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At what point do you stop replacing things? At this point you could also replace piston rings, valve stem seals, etc etc. I've struggled in determining what I will be doing when I take my engine apart, but have to draw the line somewhere.
In my case I will be drawing the line (temporarily) with the bottom end. I first acquired Absurdflow parts, then I figured it would be an inefficient waste if I limited power output to what stock rods will handle on track and still let me drive it home. So I got M-tuned rods and I figured that since the bottom end is getting pulled I might as well do pistons too. The Supertechs need a 0.50mm overbore, and while it's at the machine shop I might as well have the new rotating parts balanced. A set of Boundary OPGs isn't a bad idea, of course new bearings & seals, and a set of Mazdacomp motor mounts.

I'm drawing the line at the bottom end for budget reasons as I still need to spend money on a 6-spd and new front brakes. I don't own an engine hoist, will be borrowing one and I don't want to schlep it around or pull the motor & tranny any more than once if I can help it. The head and an intake mani will be addressed at some point in the future, but I can R&R those parts by myself and without having to borrow somebody else's tools to do it. As far as I'm concerned, anything above the block doesn't necessarily have to be done "while I have it out of the car...." so that's where I draw the line.
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Old 11-18-2010, 01:12 AM   #26
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In my case I will be drawing the line (temporarily) with the bottom end. The head and an intake mani will be addressed at some point in the future, but I can R&R those parts by myself and without having to borrow somebody else's tools to do it. As far as I'm concerned, anything above the block doesn't necessarily have to be done "while I have it out of the car...." so that's where I draw the line.
This is a very intelligent plan of action for the reasons you mention. Doing the complete bottom end makes the most sense. Honestly if you can't afford to do the bottom end on a Miata you shouldn't be making enough power to break it.
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