Piston question

[Daniel2019]

Ok so I've got into contact with someone who will take my already disassembled engine..

Apparently because I have taken the pistons out myself (Fraz, actually) theyre saying that "because the pistons have been pulled out it will need to be bored to the next oversize or you will just destroy the rings on the lip if you try to put it back together as is. You will most probably need new pistons to fit the bore aswell" (Direct quote)

To me that sounds a bit odd.. Sure, if I can get away with it price wise then I'd love to bore it out to a 2.2 or something, but it seems unnecessary? Is this true or bs?

"if you go oversized pistons it will make more power aswell, hypereutectic alloy pistons are relatively cheap and usually much lighter then standard and aslong as the engine isn't forced induction will be much stronger than standard"

and "you can usually pick up hypereutectic pistons for about 300-500 a set depending on brand and availability"

Sounds like theyre just trying to squeeze more money out of me to be completely honest.

[spetz]

When they are telling you about oversize pistons they do not mean enough to make it a 2.2L.

Usually in a proper engine rebuild the cylinders are bored by 0.25mm or so and you need 0.25mm larger pistons to suit the new bore.
If the engine is in good condition it may not need this during a rebuild, however I am pretty sure pistons would need to go back in the same cylinders they came out of which might be where your issue arises seeing as the engine is disassembled already.

You can buy oversize pistons from Mitsubishi ranging from 0.25mm to 1mm oversize (maybe even more, not sure).
You cannot go much larger as the walls of the cylinders become too thin and hence too weak.
If you want to use 82mm pistons for example and have a 2.2L engine you'd need new cylinder sleeves fitted and you can likely use 4G92 MIVEC oversize pistons but keep in mind all things remaining the same your compression ratio will go up (maybe too high) and it'd be a good idea to do something about the rods. Not sure on how true it is, but you can shot peen, crack test, cryo treat etc rods which supposedly makes them stronger by about 20% to cope with the heavier pistons

[Daniel2019]

Im 99% sure Fraz knows the order in which the pistons came out. I didnt touch them because I wasnt sure what I was doing with them.

Although I guess the issue is are they in the same order as he left them. (Fraz, we should have labelled them! Damn it!)

I was under the impression that the cylinders could just be honed.

I dont really want to have to bore it out although I suppose if I can fit it into the budget then I'll do it. Tiny bit more powar!

Thank you spetz! Exactly the kind of info that I was hoping for.

[Bennoz]

I'm not convinced you need to sleeve the bores if you bore them out, there's a shitload of meat in them. I've got the heads off my spare 6A13 at the moment, I'll flip it measure up today.

I've bored out my mini motor so far I had to sleeve no#4 because we hit a water gallery, but the bore was so big we had to offset bore 1 & 4 outward towards the ends of the engine. There less than 2mm between cylinder walls & it can rev out to 8 grand all day.



As far as piston numbers go, they are numbered from the factory, they also have an arrow to tell you which way round they go. It's stamped on the side of the big ends.

Having said that, if you pull them all out & have them shot peened etc, then you should be having them balanced to the crank & the crank balanced to flywheel - then it will make no difference what order they go in.

If you simply want to whack it all back together, then yes, depending on the condition of the bores, they could very well just be lightly honed. If they have to be bored at all to repair any damage or extreme wear, they will bore it out as small as possible (unless you specify otherwise), then the first thing you use to fill up the excess in the bore size is oversize rings. Once you exceed to the availability (and practical limitations) of over size rings, then you start with oversize pistons.

The only time I've ever seen boring as requirement to repair an engine, is the old washer off the intake manifold falling into the intake & making its way into the bore & scoring the sh*t out of it - and extreme wear. I pulled apart a 650,000km for 4L donk once, the wear on the bores was so big, you could see through the piston ring gaps. The top of the bore where the piston rings dont hit, was almost 1mm smaller than the lower section of the bore lol

[spetz]

Do the pistons look to be in good condition?
Were there any marks on the cylinder walls?

The cylinders and pistons would be measured with a micrometer and the engine rebuild manual (which you can download in pdf format) should say the minimum and maximum clearance allowances.
If the clearance is more than the manual states you'll end up with piston knock which will wear out the motor fast.

As for sleeving when boring the cylinders, I don't know if it's necessary or not. It is something that a good engine builder could tell you though if he has the bare block in front of him. If you think about it for every 1mm extra bore you are only really removing 0.5mm of material.

[Daniel2019]

Looks like I'm back to square 1 in terms of finding a place to do the rebuild then.

I may have to source this other engine off gumtree with a fucked bigend bearing as most places wont take an already disassembled engine and I'm beginning not to trust this guy that said he would do it. I can see this turning into a big f**k around and me losing a lot of extra cash through this guy.

Also, the 6A12 block is cast iron, yes?

As for the condition of things, I actually dont know. I dont really know enough to sit here and say yep theyre fine or they rooted. I havent noticed anything major, as in scratches or anything like that. The engine had a blown head gasket apparently.

Might look more into this one on gumtree with the stuffed bearing.

[Sahin]

Looks like I'm back to square 1 in terms of finding a place to do the rebuild then.

I may have to source this other engine off gumtree with a fucked bigend bearing as most places wont take an already disassembled engine and I'm beginning not to trust this guy that said he would do it. I can see this turning into a big f**k around and me losing a lot of extra cash through this guy.

Also, the 6A12 block is cast iron, yes?

As for the condition of things, I actually dont know. I dont really know enough to sit here and say yep theyre fine or they rooted. I havent noticed anything major, as in scratches or anything like that. The engine had a blown head gasket apparently.

Might look more into this one on gumtree with the stuffed bearing.

[Daniel2019]

What? Im assuming it isn't alloy. Have been told its cast iron, I'm just making sure

[spetz]

Yeah it's cast iron. Only the V8 Mitsubishi motors of that era were alloy.
The new ones are mostly alloy as well.

If you look at the pistons you can usually tell once they have quite a bit of wear and tear on them especially around the skirt area. Though as I said it'd all have to be measure with a micrometer to be sure of tolerances.

Why are they so against building a stripped motor?
With the manual in front of them it doesn't seem like it would matter?

[Daniel2019]

Yeah it's cast iron. Only the V8 Mitsubishi motors of that era were alloy.
The new ones are mostly alloy as well.

If you look at the pistons you can usually tell once they have quite a bit of wear and tear on them especially around the skirt area. Though as I said it'd all have to be measure with a micrometer to be sure of tolerances.

Why are they so against building a stripped motor?
With the manual in front of them it doesn't seem like it would matter?

If anything I thought it would be cheaper because they wouldnt have to take the time to strip it down.. but I guess that if they havent organised all the bits and pieces themselves then things get lost, could be broken and its harder to find stuff that somebody else has organised.

Will be trying to find the time to get this damn ute finally so I can get this other engine me thinks. This build is starting to get frustrating. Taking too damn long.

[spetz]

Yes the organizing of small bits must be a big issue too as everyone has their own way of organizing.

Not to mention though as a customer you should be careful as if anything goes wrong you'll just hear "well we didn't disassemble so that's what went wrong" or something similar to that.

Why aren't you trying to assemble it yourself and just get the measuring/machining done at a shop?
It seems pretty scary but just watch a bunch of videos so you build some confidence etc

[Daniel2019]

Why aren't you trying to assemble it yourself and just get the measuring/machining done at a shop?
It seems pretty scary but just watch a bunch of videos so you build some confidence etc

That was originally the plan but now that Its costing a fair amount of money Id rather have it done, have peace of mind and a warranty for the extra thousand bucks. If I were just replacing the head gasket and not spending any more money then I would but Im spending a decent amount of cash so I dont want to have them do the machine work, assemble it myself and f**k something up and have it go bang because then I'd be screwed.

[spetz]

I understand what you mean and of course the added security might be worth the extra money.

Personally though if I was in no hurry and could afford an extended down time of the car I would try to build it myself.
It'd be a great experience, it would be much more rewarding in the end and you'd be more confident to do this again some day.
I would of course take every precaution possible, dummy assemble it, and record everything with pics, documentation etc etc

[Daniel2019]

Yeah, I completely understand what you're saying.

I do kinda need the car though. Currently stealing cars in the family for work and its only a matter of time before I get a shift and dont have a car available to me.

Plus I just need to get it finished. Its been like six months since ive started this