RB20 Broken Piston Rings??

[blackrb20silvia]

hey guys

i have a few probs with my RB20 so this Q is for those that know the rb20 fairly well or any knowledge of engine building maybe sydneykid could offer some addvice

well my prob is this the car was at the auto elects for other reasons they did a compression test on the engine and found cyl 3 to be down i dont know by how much. they also said that it was leaking from the block suspect head gasket i ave the car at home now and just today pulled the head of with a friend in the mech business for bout 10 years. but as i found that when i removed the imlet i found that the leak was on a hose near the block.

When the head came off we found no break in the gasket and the bottom end looks brand new (says my friend) eaither has no kays on it or has been recentley rebiult.

Anyway the head also looks great

so what we cant work out is why the compression is bad on three it still has copmression but not much i dont know exactleywhat the reading was but the pistons look perfect

does any one know what the prob could be maybe rings?? and is there a way to check if the rings are broken with out pulling the bottom end apart??? or is there other possibilities

the head will be pressure tested through next week but i have not an idea where or what the prb could be any help from anyone woulb be great we both are stumped

thanks in advance

matt

[Ahh32]

Broken ring land. ring gap loose. rings not bed in (if just rebuilt). valves not seating fully. cracked head. cracked block. warped head or block.

The gasket doesn't need to be broken, it could be leaking into number 2 or 4 cyl. can be difficult to find at times

Mine has 80 psi in a couple of cyl's due to loose ring gaps.

If they said it was from the block, then i am assuming they did a wet test to make sure it wasn't the valves leaking.

time to pull the rest of they engine out and look at no#3 piston

[carl h]

should have done a leak down test on it first, compresson tests only let you know there is a problem.

[blackrb20silvia]

psi at all but cyl 3 where bout 115 is this corect number 3 was bout 55 does this tell anyone anything also there was no sign of any leakage any where i drove the car for bout 15 min before i checked the leak but it was all from the hose

saw the elect today he said that he did not know if it was gasket just thought it was when on the hoist water pissing out from near the block thats all so i am still getting the head checked on monday if it ok it is stayin for a port and flow and tidy up does that just leave the piston, rings and ect... as the culprit???

and do i have to pull out the motor out to check all these ( i know its a stupid Q but its worth a try )?

[blind_elk]

Factory spec is 12 kg/cm2 - I think that equates to around 160psi. So your engine, in general, appears to be in pretty poor shape. It should have had a leakdown test to locate the actual source of problem, particularly in #3, before you pulled it down.

The water leak was likely a hose, as the Japs rarely treat the cooling system with coolant, and the hoses rot from the inside. While you are doing the job, get a complete set of hoses - they will set you back around $400, but think of the labour costs to replace them otherwise.

You can replace the water hoses while the head is off. And while you're about it, do all the welsh plugs.

The rings, you will need to drop the sump - worst case, this requires the engine to be lifted off the mounts.

[blackrb20silvia]

thanks man the advice is great but the head came off 2 days ago cuz i was told the head gasket was ***ed anyway does it matter should an experianced engine shop tell me what is wrong or have i ****ed up and taken the head off to soon

as for labour i have never paid $1 in labour for any mech work i am pretty good with a spanner and have good friends in the trade who in a good way will come round and help but just sit there and tell me what to do it is the best way to learn and the easiest way not to **** up (thanks dave)

but anyway if worse comes to worse how bad can it be if the compression is down at 115 on all the other cyl would i be looking at a new rebuild cuz looks fresh as the bore still has machine swirls sort of thing and there is no lip from where the rings stop pistons look great ???

is it possible to just replace the rings and shit or do i need new pistons even if they are in great shape

the reason i ask is the missus wants to move to sydney asap otherwise i would save and bye forged and do the lot head and bottom end but i have to do this asap

i suppose my Q is that if i took the head to the engine place will he be able to tell if there is anything wrong with it ???

if there is notthing wrong with it does this mean it has to be bottom end. EI.... rings ect..

[blind_elk]

It's not my money, so take this advice with a grain of salt. If you are having the head fully checked over, make sure all the valves are reseated - you may get back the compression you lost in #3. But since the engine is already half apart, drop the sump, and remove the pistons and check the rings.

I am guessing that you are going to have to put it all back together again to do the leakdown, then possibly pull it all apart again to fix the problem revealed by the leakdown.

[blackrb20silvia]

advice appreciated thanks

as for money it costs what it costs i dont care

but your saying that i have to put the engine back together just to leak test it????

there has to another way surley?

if it came to that i would by the forgies and rings get the block honed and the head flowed i dont want to have to put the head on just to test and yes if they find that the valves are the cause ill be doing them to

what are your thought and head work for the RB20 blind elk??

also lets just sat that the head comes back tested fine

it could only be piston and ring prob am i right???

if so can i just change the rings if the pistons are fine???

[blind_elk]

I'm not an engineer, so, again, "grain of salt". Unless you are making mega kw with the engine, I believe the pistons will withstand well in excess of the standard output of a RB20. So I think forgies are an unnecessary expense at this time.

Unfortunately, you can't test for leaks on an open bottle, same with a disassembled engine. Although engine builders may have some sort of gizzmo to do it - ask their advice.

A bit of headwork won't go astray - clean up / smooth out the ports, maybe a bit of profiling and matching to the manifolds. As part of the work, make sure you specify re-seating the valves.

I think it's unlikely to be a piston problem - I think any damage would more than likely be visible as the engine sits right now. It may be a problem with the bedding of the rings, given that it may be a recently rebuilt engine. If you pull the pistons out, take them to an experienced engine builder for an opinion.

[blackrb20silvia]

I'm not an engineer' date=' so, again, "grain of salt". Unless you are making mega kw with the engine, I believe the pistons will withstand well in excess of the standard output of a RB20. So I think forgies are an unnecessary expense at this time.

well now that you mention HPhere is a pic of the turbo setup

i have invested a lot of money evrywhere else in the car so maybe its worth while just to do the whole lot???

i just wanted to do it the easiest way cuz i got to move soon so the cheapest way would have been the best for me anyway fingers crossed its not major ill post later on monday when i know whats going on with the engine for your opinion on where to go from there you help is much appreciated as with all the others that have offered there opinion on the subject

please feel free to comment id like to have a few options if there are any

also what is the usual cost of a full rebuild i can get forged pistons for bout 800 dont know if that includes rings what else do i need and approx cost me and a mech friend can assemble but what are the usuall costs of what ever else i need to do?????

matt

[img']http://img90.exs.cx/img90/3207/silviaturbo16dj.gif[/img]

[blackrb20silvia]

also what is the usual cost of a full rebuild i can get forged pistons for bout 800 dont know if that includes rings what else do i need and approx cost me and a mech friend can assemble but what are the usuall costs of what ever else i need to do?????