How hard is it to install new forged pistons?

skywalker · 10-16-2001, 01:07 AM

Say I have a block that has been used for 30K miles. Now I personally want to put in new lower compression forged pistons. What are some things I have to look out for? Or is it really that easy as to take out the old out and slap the new ones in?

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ColinL · 10-16-2001, 01:21 AM

it's not easy. extreme attention to detail and proper torque values per the Factory Service Manual are a must.

i'd put money on a stock shortblock assembled in Gunma lasting longer than a shortblock with exotic components assembled by Joe Shadetree Mechanic. expensive parts put together poorly just make an expensive mess!

that said-- with the FSM, time and a knowledgable friend or two there's nothing impossible about it. just ask 8Complex!

skywalker · 10-16-2001, 01:30 AM

Ok, thanks for the info. Now would it be worth adding on Stronger Connecting Rods if I am running 300Hp or not? I have not heard of anyone breaking one yet so i would assume they are strong enough to hold that muhc power. I don't plan to go above that 300HP mark, so if the stock ones will work I would like to stay with them.

So if i want lower compression pistons I better find someone that can do it for me, or I have a lot of research to do and an informative friend that has done this before.

iodine23 · 10-16-2001, 01:49 AM

I think I read somewhere that increasing RPM is more taxing on the engine than increasing power. Not sure where though, I can see if I can find out.

Andrew · 10-16-2001, 02:31 AM

bill, are you planning on going to adams house or something or were you going to buy a hoist and do it at your place?

im leaning towards just buying the pistons as well and keeping everything on the safe side while being able to take high boost without worries. I definitely want to be there for this and help do whatever i can (and I espeically want to be there so i can learn more). I might end up paying adam to do it (if hell help me that is ) for me or maybe have Red Star do it while the engine is tore down.

so many things to get this car running bullet proof and so few dollars in my pocket

question for those who have done this: how long did it take? how many people were working on the car? did you have to take breaks to go to the autoparts store for various things?

also bill, remember about the .2 overbore though to correct everything that subaru did wrong...wouldnt it be better to have everything done at one place?

8Complex · 10-16-2001, 04:07 AM

I'm gonna start in the middle here. If you're looking at running a fairly high compression motor with a good amount of boost (9:1 with 15psi) then you'll probably want rods as well. Rods break/bend during the midrange power when the torque gets high, though sometimes go when revving too high as well.

Swapping pistons in, having done it before, isn't such a big deal - however you need to have at least 1 specialty tool on hand, as well as a hard-to-find 14mm allen socket. The one tool you NEED is the Subaru specific piston pin remover and installer tool. Absolutely essential.

The manuals... yeah, they're helpful but you don't NEED them if you're very mechanically inclined and willing to take a LONG time doing it. Honestly, the only thing that I'd need them for now is the torqe specs and procedure for the head bolts.

Really, it takes a lot of patience and fumbling with the piston pin tool, but it's not horribly difficult.

Pulling the motor isn't too bad if you have a good hoist, and the motor isn't even that heavy, either. One definite recommendation that I have (and this is a damn good one, so pay attention) is to buy one of those small plastic cabinets with all the drawers for screws, etc in it and put all the bolts in those as you take them out and label them with masking tape as you put them in there. You won't be sorry that you're taking the extra time to be more organized, I guarantee, and you will know what I mean as soon as you go to put it all back together.

bsquare · 10-16-2001, 04:25 AM

You might consider having the stock rods stress-relieved/shot peened. This would greatly increase their durability without the cost of forged rods (though they won't be quite as strong or light).

Ben

skywalker · 10-16-2001, 11:56 AM

8complex, want to drop by my house?

8complex,

Did you put in new connecting rods or not? Just curious, and how much boost are you planning to run? Enough to blow by a WRX?

When swapping pistons, if I have a 14mm allen wrench and a Subaru Specific Pin Remover are there any other measuring devices I might need? Something to make sure the rings will fit well? I guess getting all the specs on the engine is what I really need to do first. Does anyone have a manual I could get a copy of?

As for a hoist I have a access to a big mofo hoist, so no worries there.

bsquare,

Do you know what type of place or where I would have my stock rods stress-relieved/shot peened. Ha ha, very funny...

ColinL · 10-16-2001, 02:03 PM

Quote:

Do you know what type of place or where I would have my stock rods stress-relieved/shot peened.

Actually any engine rebuilder / machine shop worth their salt can do this... magnaflux, shot-peen and balance the rod/piston combos. Doesn't matter what make or application.

bsquare · 10-16-2001, 03:17 PM

Quote:

Do you know what type of place or where I would have my stock rods stress-relieved/shot peened. Ha ha, very funny...

What's funny? I'm totally serious.

Ben

skywalker · 10-16-2001, 03:27 PM

Rods... Sorry, nasty mind of mine...

Anyway I talked to CobbTuning today about a bullet proof engine. They recommended a closed deck block with new Forged Conrods and Forged Pistons, including the rings and pins of course. So I am thinking I might look into this a little further.

My only other question is when would be a good time to upgrade the valve stems and springs? Or shoudl I bother if I am keeping stock RPM's of 6200?

Idea's? I am looking for say about 280-300 Hp and I want a safe reliable setup.

bsquare · 10-16-2001, 04:04 PM

300hp? You don't need forged internals for that at all, unless you mean 300 to the wheels, in which case you will definitely need lower compression pistons, a closed deck, etc. 300hp at the crank from a turbo EJ25 is fairly straightforward.

Ben

8Complex · 10-16-2001, 04:33 PM

Quote:

8complex, want to drop by my house?

Hey man, I'm unemployed. For enough money, who knows...

Quote:

Did you put in new connecting rods or not? Just curious, and how much boost are you planning to run? Enough to blow by a WRX?

When swapping pistons, if I have a 14mm allen wrench and a Subaru Specific Pin Remover are there any other measuring devices I might need? Something to make sure the rings will fit well? I guess getting all the specs on the engine is what I really need to do first. Does anyone have a manual I could get a copy of?

No, I went back 100% stock when I fixed mine, just got a used piston and scrapped rings from other pistons I had laying around (since the one that came out had a couple of screwed rings).

2psi on a 10:1 compression setup is enough to hang with a stock WRX (I've done it 0-110, and yes it was completely broken in... *shrug*), so it's not hard to make anything that'll just pass it up, especially if you're looking at lower compression and higher boost.

There are tools and procedures to make sure the pistons and rings fit well in the cylinders. For the pistons, just have to measure the dia. and the bore of the cylinder. I think Subaru's ideal clearance is .5mm between dia.'s (.25mm at each edge). The rings are tougher but not too bad. You just have to slip them (not on the pistons) into the cylinders and then measure the gap between the ends of the ring to see how well they fit. I don't remember what the tolerances are for those, I never measured them myself.

Just FYI, the block I hacked back together to put in my car compression tested really well 177(1)-170(2)-177(3)-170(4) and ran great (rather surprisingly). I will soon have another new stock block in the car though (don't ask).

Jay_UK · 10-16-2001, 06:23 PM

Howdy...

IMHO.. change the pistons and rods.

The pistons can be changed without splitting the blocks... just remove the heads.

To change the rods, you have to split the block.

Yes you do need a big allen key to remove the wrist pin plugs.

You dont need the speciality wrist pin tool... a set of long nose pliers and wire will do at a push.

A piston ring compressor is obviously required.

You will need some 12 point sockets too.

I'd suggest you plastigauge the mains and big ends while you split the block.

The Service manual is required... mainly for torque values and tightening sequences... but I'm sur eif you ask nicely they will photocopy the required pages.

Any issues mail me.. I've built a few engines subie engines...

J.

10-16-2001, 01:07 AM	#1
skywalker Scooby Specialist Member#: 1990 Join Date: Jul 2000	How hard is it to install new forged pistons? Say I have a block that has been used for 30K miles. Now I personally want to put in new lower compression forged pistons. What are some things I have to look out for? Or is it really that easy as to take out the old out and slap the new ones in? * Registered users of the site do not see these ads.

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10-16-2001, 01:21 AM	#2
ColinL Scooby Guru Member#: 114 Join Date: Jul 1999 Chapter/Region: MWSOC Location: Wichita, KS and Whoring, OT Vehicle: '03 Evo, Rice White '01 Erion CBR 929	it's not easy. extreme attention to detail and proper torque values per the Factory Service Manual are a must. i'd put money on a stock shortblock assembled in Gunma lasting longer than a shortblock with exotic components assembled by Joe Shadetree Mechanic. expensive parts put together poorly just make an expensive mess! that said-- with the FSM, time and a knowledgable friend or two there's nothing impossible about it. just ask 8Complex!

10-16-2001, 01:30 AM	#3
skywalker Scooby Specialist Member#: 1990 Join Date: Jul 2000	Ok, thanks for the info. Now would it be worth adding on Stronger Connecting Rods if I am running 300Hp or not? I have not heard of anyone breaking one yet so i would assume they are strong enough to hold that muhc power. I don't plan to go above that 300HP mark, so if the stock ones will work I would like to stay with them. So if i want lower compression pistons I better find someone that can do it for me, or I have a lot of research to do and an informative friend that has done this before.

10-16-2001, 01:49 AM	#4
iodine23 Scooby Specialist Member#: 4071 Join Date: Feb 2001 Location: Austin, TX Vehicle: 2001 Impreza 2.5RS Blue Ridge Pearl	I think I read somewhere that increasing RPM is more taxing on the engine than increasing power. Not sure where though, I can see if I can find out.

10-16-2001, 02:31 AM	#5
Andrew Scooby Specialist Member#: 1170 Join Date: Mar 2000 Chapter/Region: BAIC Location: San Jose, CA Vehicle: 2005 STi White	bill, are you planning on going to adams house or something or were you going to buy a hoist and do it at your place? im leaning towards just buying the pistons as well and keeping everything on the safe side while being able to take high boost without worries. I definitely want to be there for this and help do whatever i can (and I espeically want to be there so i can learn more). I might end up paying adam to do it (if hell help me that is ) for me or maybe have Red Star do it while the engine is tore down. so many things to get this car running bullet proof and so few dollars in my pocket question for those who have done this: how long did it take? how many people were working on the car? did you have to take breaks to go to the autoparts store for various things? also bill, remember about the .2 overbore though to correct everything that subaru did wrong...wouldnt it be better to have everything done at one place?

10-16-2001, 04:07 AM	#6
8Complex Moderator Member#: 922 Join Date: Feb 2000 Chapter/Region: MWSOC Location: Schaumburg, IL Vehicle: 04 FXT Red	I'm gonna start in the middle here. If you're looking at running a fairly high compression motor with a good amount of boost (9:1 with 15psi) then you'll probably want rods as well. Rods break/bend during the midrange power when the torque gets high, though sometimes go when revving too high as well. Swapping pistons in, having done it before, isn't such a big deal - however you need to have at least 1 specialty tool on hand, as well as a hard-to-find 14mm allen socket. The one tool you NEED is the Subaru specific piston pin remover and installer tool. Absolutely essential. The manuals... yeah, they're helpful but you don't NEED them if you're very mechanically inclined and willing to take a LONG time doing it. Honestly, the only thing that I'd need them for now is the torqe specs and procedure for the head bolts. Really, it takes a lot of patience and fumbling with the piston pin tool, but it's not horribly difficult. Pulling the motor isn't too bad if you have a good hoist, and the motor isn't even that heavy, either. One definite recommendation that I have (and this is a damn good one, so pay attention) is to buy one of those small plastic cabinets with all the drawers for screws, etc in it and put all the bolts in those as you take them out and label them with masking tape as you put them in there. You won't be sorry that you're taking the extra time to be more organized, I guarantee, and you will know what I mean as soon as you go to put it all back together.

10-16-2001, 04:25 AM	#7
bsquare Scooby Specialist Member#: 1911 Join Date: Jul 2000 Location: Seattle, WA, USA Vehicle: 2000 Impreza 2.5RS Silverthorn Metallic	You might consider having the stock rods stress-relieved/shot peened. This would greatly increase their durability without the cost of forged rods (though they won't be quite as strong or light). Ben

10-16-2001, 11:56 AM	#8
skywalker Scooby Specialist Member#: 1990 Join Date: Jul 2000	8complex, want to drop by my house? 8complex, Did you put in new connecting rods or not? Just curious, and how much boost are you planning to run? Enough to blow by a WRX? When swapping pistons, if I have a 14mm allen wrench and a Subaru Specific Pin Remover are there any other measuring devices I might need? Something to make sure the rings will fit well? I guess getting all the specs on the engine is what I really need to do first. Does anyone have a manual I could get a copy of? As for a hoist I have a access to a big mofo hoist, so no worries there. bsquare, Do you know what type of place or where I would have my stock rods stress-relieved/shot peened. Ha ha, very funny...

10-16-2001, 03:27 PM	#11
skywalker Scooby Specialist Member#: 1990 Join Date: Jul 2000	Rods... Sorry, nasty mind of mine... Anyway I talked to CobbTuning today about a bullet proof engine. They recommended a closed deck block with new Forged Conrods and Forged Pistons, including the rings and pins of course. So I am thinking I might look into this a little further. My only other question is when would be a good time to upgrade the valve stems and springs? Or shoudl I bother if I am keeping stock RPM's of 6200? Idea's? I am looking for say about 280-300 Hp and I want a safe reliable setup.

10-16-2001, 04:04 PM	#12
bsquare Scooby Specialist Member#: 1911 Join Date: Jul 2000 Location: Seattle, WA, USA Vehicle: 2000 Impreza 2.5RS Silverthorn Metallic	300hp? You don't need forged internals for that at all, unless you mean 300 to the wheels, in which case you will definitely need lower compression pistons, a closed deck, etc. 300hp at the crank from a turbo EJ25 is fairly straightforward. Ben

10-16-2001, 06:23 PM	#14
Jay_UK Scooby Specialist Member#: 296 Join Date: Sep 1999 Location: Derby, Derbyshire, England	Howdy... IMHO.. change the pistons and rods. The pistons can be changed without splitting the blocks... just remove the heads. To change the rods, you have to split the block. Yes you do need a big allen key to remove the wrist pin plugs. You dont need the speciality wrist pin tool... a set of long nose pliers and wire will do at a push. A piston ring compressor is obviously required. You will need some 12 point sockets too. I'd suggest you plastigauge the mains and big ends while you split the block. The Service manual is required... mainly for torque values and tightening sequences... but I'm sur eif you ask nicely they will photocopy the required pages. Any issues mail me.. I've built a few engines subie engines... J.