fitting new m-tuned rods
 

I only plan to fit m-rods to my 1.8 not planning a full overhaul as the engine appears to be in good condition 5% leakdown.
What I was wondering is should I use the original bearings from my old rods or should I fit new bearings in..........If i fit new bearings is it necessary to run it in on mineral oil or will it be ok on synthetic..
any help much appreciated thanks.

If they look flawless/brand new with no wear/scuffing/etc on em there's no reason you can't reuse.
As for break in, there are tons of different opinions, IMO I'd use regular for the 1st couple hundred miles.
my .02

are you installing new rings?

If you're going to the trouble and expense to put in better rods, don't cheap out on the bearings. If I had an engine that far apart it would get new main and rod bearings.

As for break in oil, what 90R said... are you using new rings?

If you've honed the cylinders and installed new rings don't use synthetic. Despite the 5% leakdown numbers I'd probably do a hone/rings just due to having disturbed everything during the disassembly/reassembly process.

And since they're used bearings, they won't look brand new, and you should replace them. ;)

I wouldn"t condemn then before a round of plastigauge. I'd be more concerned about the ring seal after reassembly.

I once ran my 323gtx w/o oil. The new bearings were looser than the oldass "worn" bearigns accordign to the plastigauge. I put oil in it and the knock went away. I still have that package of bearings somewhere in my attic.

atleast get rod bearings you will not be removing the crank so there is no need for main bearings if the originals are in good shape.

Get the small end measured as well. I had to hone mine a touch to fit FM Wisecos.

You generally don't need to remove the crank to replace mains... just one main cap at a time.

Plastigauge is for wankers... use real measuring tools.

and why the hell would you do that if there is no problem and, you dont have the chance of contaminating it ie dissasemble and, reasemble it. it is 50 dollars wasted and time wasted as well.

Iam keeping original pistons and rings.no honing.
How do you hone the small end to get it to fit. Just use fine grade emery? or a small fan buff wheel in a drill?

If you remove the pistons from the bore you must use new rings and hone it. Just a bottle brush hone will do the trick, but you have to do it. You will never.. EVER get the rings lined up in the bore exactly as they were before you removed them. That will cause sealing issues, bad compression etc. If you can manage to keep the pistons in the bore while installing new rods, more power to you... but don't pull them out and put them back as they are.

/\ I agree

Awww fook now this makes me think getting new pistons and rings might be better idea.

Sorry, what is this "contamination" you speak of when building engines?

I have a phrase that Rennkafer told me when we were building my first motor - "Cleanliness before Godliness"

i implied a possible not an imperative.

Grow a sack:loser:,get new forged pistons AND:facepalm: rings and balance that shit as well,crank,rods and pistons.

Balanced motor sound and smoothness = better than college sex:makeout:

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 shite.

Maybe I'm just a distrustful bastard... I've seen inside too many "professionally" built engines at work to trust anything I didn't do myself.

if i remove pistons rods and crank is there much more to remove so that i can take block for a rebore?

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.

Omniman just used heat on the small end.

+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.

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.

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.