Whats the general consensus on here about doing standard size drop in pistons? I need to replace my headgasket and I'm doing a turbo swap so since the car will be down for a bit and the head will be off I was thinking of just doing pistons, rods and bearings as well. Is this worth doing or is it only possible to do pistons with a bore? I saw a vendor selling weiscos that are in standard bore size so I was considering it.

 

Honestly, it's a half assed way of doing things. Just do your mods and tear it down in winter. It's been done before and some people have gotten away with it, but it wouldn't give me piece of mind.

 

To do it correctly the bores still need to measured, and likely honed. So the machine is still involved. Unless you have the tools to measure the cylinder, and a hone. Those tools will cost more than have the machine shop do it...lol. And yes, the motor will come out of the car for this...

 

Its common practice (relatively speaking) to do drop-in in UK, and well practiced offer by Buschur in Ohio and English Racing in Pacific North West, to mention two reputable sources.

Although I agree that on paper the (only) best way to upgrade is proper engine build, in practice...if present pistons/rings seal fine there is little concern/reason to assume or risk to dropping in same sized quality pistons.

Honing is required to clean up/roughen up cylinder surface to allow new rings to properly break in and seal: I subscribe to the hard break-in on dyno...if you pursue this method.

Many have done it and it works.
Honing tools are dirt cheap, and a simple drill can be used to perform by hand the hone, youtube vidoes aplenty show how.
Cleanup fastidiously.
New rod bearings a must.
Assemble, and perhaps take to pro to break in hard on dyno, before continuing to break-in gently for 1000+ miles on street in more traditional way.
Hard break in is to seal rings.

 

Only way I'd consider it is on a low low low mileage car.

 

This would give you the best chance that the cylinders measured to be in spec.

Honestly, it wouldn't matter how many miles are on the car as long as everything are within the measurement spec.
At the end of the day, full machine, drop in, all require the clearances to check out between piston and bore.

Honing a cylinder is very very easy and can be relatively cheap thing to do.
Being sure you grind the piston ring gap properly is also very important aspect.

If you know what you are doing, have the tools, either is fine really.

 

Why would mileage matter? If bores aren't out of round or out of spec mileage shouldn't mean anything.

 

I'm in a similar situation. Where can we find OEM specs for bores, pistons, rings, conrod bearing oil clearance, etc?

I have access to calibrated bore gauges and micrometers that are accurate to a micron. I plan to check the bores for diameter at a range of depths/directions as well as check for roundness and cylindricity the best I can with just the head off.

At my job I'm used to targeting a range of +/- 3 microns for piston/wall clearance as well as main and rod oil clearances. I know I don't need to be anywhere near that precise for my engine but I would like to make sure its within spec.

 

Agree

 

I'd think anyone with a clue would understand. Years of cold starts and abuse would steer me far far away of doing a half assed drop in job. If you're going to do it do it right the first time. IMO

Do whatever the f you want not my money or motor.

 

all the spec are in the workshop manuals that you can download from the evoscan site...

problem is... stock spec is given for a naked block.. i.e. with no head..
once you torque the head on the PTW spec goes out of the window..

here is my 80 000 km engine measurements... with and without the head torqued on the block..

 

Hey, thanks for the detailed info! I'll take in to account the 20-24 micron change on the top-cross torqued measurement. At least knowing all of the offsets you had should help me ball park it a lot better than without that info.

Which type of ARP studs and what torque spec you used for those measurements? I've seen so many different torque values thrown out for head bolts/studs. I can't believe there isn't a specific standard that EVERYONE follows for a given stud or bolt.

 

this is the "before" measurement... done with stock bolts

for machining I used a torque plate and arp studs with the torque settings that they specify

 

No offense, but your reply is garbage.
He's asking for a technical understanding why its a poor choice and you given none.
I'd be curious to why you view drop in pistons as half assed?
A piston the size of a standard bore is my understanding of drop in piston.
The only 'correct' way to build a motor is to oversize a piston and machine a block?
...that is not true.

A more realistic answer would be the risk of using a high mileage block which potentially has internal stress cracks.
However, where do all the core blocks go when you buy a complete motor?
They get checked and cleaned and machined and back out again.

Ultimately, what is the original posters goal?
If seeking for a healthy amount of power like 600+whp, seems like higher risk.
But perhaps 4-500whp should be no problem

 

I've seen videos of factories where engines are being assembled (not the Mitsubishi engine plant) and I notice racks with preselected pistons on it, one for each hole. Now maybe if the same tool bored every cylinder this wouldn't be necessary but they bore them all at the same time.

To point out the obvious, a cylinder that wears doesn't get smaller. On top of that you are going from a cast piston to a forged piston and forged pistons require more clearance. So there's some reasons a forged standard sized piston just dropped in may cause problems. At least on a nearly new engine you have more of a chance of it being satisfactory.

Anyway, the OP asked for a consensus not a technical answer. A consensus is a group of opinions.