Help - should I rebuild my rb25 (pics in post)

[Desean Strickland]

Hey guys 

So I took the head off my rb25 to install arp head studs and replace the head gasket and have found that 3 of my pistons look like this…

Looks all worn and uneven only on the intake side of the piston. Also the exhaust valves have a bunch of build up on the bottoms. The bores still look fine with decent crosshatching and compression is fine with about 150 per cylinder.

My Question is what causes the pistons to wear around the edges like that and is the crap built up on the bottom of the valves related or something different?

and most importantly can I send it (obv after I clean it up) or should I be considering a rebuild

Cheers for any help 

[The Bogan]

Is that not just alot, and I mean, ALOT, of carbon build up from possibly a over rich tune/fueling issue, or, lots of blow by

How many Km is on the engine

Have you tried cleaning it off

I would definitely give it all a good clean first

You could do the same with the piston tops, just be aware to avoid contamination

Do each piston at around TDC, block off all water and oil ports, as well as the pistons that are down, then clean out any left over crub between the piston and bore with compressed air

I've watched simular cleaning techniques on other YouTube vids using chemicals with plastic scrappers, plastic scouring pads, and brass wire brushes with excellent results

Have a Google 

In the end cleaning should be your first point of call to see how bad, if at all, it really is

Hopefully it is all just carbon and some manual labour will clean it all up

 

[Duncan]

Second thing first, I'm really not sure what is on the bottom of the intake valves, carbon build up is not normally white. Also, I hope the cams are still in because some of those valves are open (if not, valve stems are bent).

Depending on your plans other than a new head gasket, it is a good time to get a head job anyway; even if it is only a factory spec rebuild at least all your stem seals, valve guides and valve seats will be good. New springs are a good idea in an older engine that will be pushed as well. Head shop will tell you what is happening on the valves

For the piston, I don't think that is normal but it's hard to tell as that is very close up. Is there only one piston that looks like that, and how does the matching head chamber look....I'm concerned it might be pinging lightly but for a long time.

And yes, some idea of the klm on the engine might help.....overall the pistons look super clean (or is that just a flash making it look silver?) which is unusual in a factory engine after all this time.

[Desean Strickland]

  On 26/01/2024 at 8:19 PM, The Bogan said:

Is that not just alot, and I mean, ALOT, of carbon build up from possibly a over rich tune/fueling issue, or, lots of blow by

How many Km is on the engine

Have you tried cleaning it off

I would definitely give it all a good clean first

You could do the same with the piston tops, just be aware to avoid contamination

Do each piston at around TDC, block off all water and oil ports, as well as the pistons that are down, then clean out any left over crub between the piston and bore with compressed air

I've watched simular cleaning techniques on other YouTube vids using chemicals with plastic scrappers, plastic scouring pads, and brass wire brushes with excellent results

Have a Google 

In the end cleaning should be your first point of call to see how bad, if at all, it really is

Hopefully it is all just carbon and some manual labour will clean it all up

 

Expand  

Iv already cleaned the piston in the first pic and it looks exactly the same, it definitely isn’t just carbon buildup. And the engine has 200,000kms and was burning heaps of oil from the turbo seal failing prior to pulling it apart, it didn’t run for long while burning oil.

Edited January 27, 2024 by Desean Strickland

[Desean Strickland]

  On 26/01/2024 at 8:29 PM, Duncan said:

Second thing first, I'm really not sure what is on the bottom of the intake valves, carbon build up is not normally white. Also, I hope the cams are still in because some of those valves are open (if not, valve stems are bent).

Depending on your plans other than a new head gasket, it is a good time to get a head job anyway; even if it is only a factory spec rebuild at least all your stem seals, valve guides and valve seats will be good. New springs are a good idea in an older engine that will be pushed as well. Head shop will tell you what is happening on the valves

For the piston, I don't think that is normal but it's hard to tell as that is very close up. Is there only one piston that looks like that, and how does the matching head chamber look....I'm concerned it might be pinging lightly but for a long time.

And yes, some idea of the klm on the engine might help.....overall the pistons look super clean (or is that just a flash making it look silver?) which is unusual in a factory engine after all this time.

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Yeah cams are still in, the silver look on the pistons in the first 2 photos is because I cleaned them to see if it was just carbon buildup, which it isn’t. Engine has 200,000kms and it is 3 pistons which has notable wear around the edges

[GTSBoy]

Build up on valves is possibly zinc or calcium or some other metal from oil being burnt.

[The Bogan]

  On 27/01/2024 at 1:31 AM, Desean Strickland said:

Iv already cleaned the piston in the first pic and it looks exactly the same, it definitely isn’t just carbon buildup. And the engine has 200,000kms and was burning heaps of oil from the turbo seal failing prior to pulling it apart, it didn’t run for long while burning oil.

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In that case it's rebuild time, or LS............nah, cheaper to rebuild everything you've got, as long as the block and head checks out fine

[Desean Strickland]

  On 27/01/2024 at 7:44 AM, GTSBoy said:

Build up on valves is possibly zinc or calcium or some other metal from oil being burnt.

Expand  

True, I never thought of that.

Iv seen u in other threads and u seem to know a lot, so roughly how much do u reccon it would cost me to get the engine rebuilt if I’m pulling the engine and just dropping the short motor off to the engine builder? Obviously I would have to get forged pistons Cus those ones are ruined, probably an mls head gasket and arp studs and just the rest close to stock? Assuming my block and crank are reusable.

I know that’s a question for an engine builder and I’ll try and get some quotes on Monday but just from either your own experience or from what you’ve heard from others, how much u reccon it will cost me if I’m pulling the motor and all they have to do it just rebuild it?

[GTSBoy]

Yah, it's real hard to be anywhere near accurate. Even a light duty build with some reused parts is approaching $10k these days though.

[admS15]

As gtsboy said, 10k AUD is a rough figure for a forged rebuild. Where are you located?

Is it only 3 of the pistons that have what appears to be detonation damage on them?

If so, a cheaper way out would be to replace the 3 pistons with some good 2nd hand ones, new rings, bearings, hone cylinders, new OEM head gasket, arp headstuds, clean up all the built up crap on the valves, service head and send it. If you can do the bottom end yourself, could save yourself a lot of $.

Recently did this with my engine, did also add some cheap forged rods, total cost was less than 2k AUD.

Whatever you do, once back together. You're going to have to address what caused the problem initially. Probably tune or fuel quality related would be my guess.

 

[Desean Strickland]

  On 27/01/2024 at 12:34 PM, admS15 said:

As gtsboy said, 10k AUD is a rough figure for a forged rebuild. Where are you located?

Is it only 3 of the pistons that have what appears to be detonation damage on them?

If so, a cheaper way out would be to replace the 3 pistons with some good 2nd hand ones, new rings, bearings, hone cylinders, new OEM head gasket, arp headstuds, clean up all the built up crap on the valves, service head and send it. If you can do the bottom end yourself, could save yourself a lot of $.

Recently did this with my engine, did also add some cheap forged rods, total cost was less than 2k AUD.

Whatever you do, once back together. You're going to have to address what caused the problem initially. Probably tune or fuel quality related would be my guess.

 

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Yeah iv thought of doing it myself but if I did I would probably rather go with some 86.0mm forged pistons and just spend the extra 1.3k while I’m in there and just re use my stock rods

how did u hone the cylinders? Did u send it to a machine shop or did u just do it yourself?

im in WA, about 2.5 hours away from Perth so my options are kinda limited.

and yeah after I finished cleaning all the pistons today it’s more like 5 of the pistons have detonation damage. 

either way it’s gonna get re-tuned when I’m done. The stock turbo seals blew causing it to slowly burn oil for a while so that could have been the cause. 

Edited January 27, 2024 by Desean Strickland

[admS15]

I honed the cylinders myself with a  3 stone hone. If I was to use forged pistons, I definitely would've got a shop to do it to make sure the clearances where spot on. 

Probably best to get a shop to look at the block before buying the pistons and see what size they recommend.

[Duncan]

Lots of external stuff could cause a problem, it looks like lots of light pinging rather than massive hits which can also damage the head, crack ring lands even spin rod bearings.

Fuel pump would be worth replacing if it is original and get the injectors cleaned and tested too. Is it a stock ECU?

Once the rebuilt engine is in you should run it in on a dyno to check everything.

[Desean Strickland]

  On 27/01/2024 at 9:28 PM, Duncan said:

Lots of external stuff could cause a problem, it looks like lots of light pinging rather than massive hits which can also damage the head, crack ring lands even spin rod bearings.

Fuel pump would be worth replacing if it is original and get the injectors cleaned and tested too. Is it a stock ECU?

Once the rebuilt engine is in you should run it in on a dyno to check everything.

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yeah im guessing the piston rings are fine coz it has 150-155 compression

it was stock fuel pump which iv just replaced with a walbro 460, have done the wiring relay mod as well, it had a haltech platnum pro already installed and tuned by C-red and basically just made stock power, iv also got a hypergear g3 highflow and the 980cc injector kit from Efi to put in.