Acl Product Warning! Rb30/25 Hybrid Buildup

[Sydneykid]

Hi Tonk, had a quick read of this thread, there seems to be one bit of IMPORTANT info that has been asked to be confirmed and it hasn't.

So, I will ask it again...........

Are you sure the ACL spec sheet said 0.007" piston to bore clearance?

I have NEVER seen an RB engine with that sort of clearance.

The forged piston rule of thumb is 0.001" for each inch of bore (86 mm = 3.4")

So I would have thought 0.003" to 0.004" would be the clearance.

Standard RB26DETT cast piston to bore clearance is 0.035 - 0.055 mm (0.001" to 0.002")

Do we have a mm versus inches mix up?

If the expansion rate of the piston doesn't need that sort of clearance (0.007"), then you have the typical cock in a sock problem. From what I can see in the picture, I would not be surprised if that was in fact the case.

Maybe the problem here is the ACL spec sheet has the incorrect (ie; too large) piston to bore clearance. And that is something I can check tomorrow while I am in the machine shop, there is an ACL spec sheet there. I will be working (YAHOOOO) on my new RB31DET (it has JE pistons).

cheers

Edited October 12, 2005 by Sydneykid

[Sweetleaf]

Ive used one set of ACL forged pistons and found the bottom of the skirt is wider than the top just below the oil ring pack.I rang ACL and they said this is correct so make sure the clearance is for top or bottom of the piston.The pistons were for a blowen V6 commodore and Nissan ones maybe different,the other strange thing was the 027tho 2nd ring gap also said to be correct by ACL.The car is not running yet so i dont know how good it is yet but i have driven some strong Skylines with ACL pistons.

[proengines]

I just checked 2 sets of pistons, one ACL and one Ross which are both the same piston. At the nominal bore size they run .004" clearance at the bottom of the skirt and have .002" taper from the bottom to the top of the skirt which is normal for a forged piston, they are smaller at the top of the skirt because it runs hotter than the bottom and expands more.

Do your pistons measure .007" smaller than the nominal bore size at the bottom of the skirt? this would be 3.3985" for .020" (.5mm) or 3.4182" for .040" (1.00mm). The bore should be 3.4055" at .5mm or 3.4252" at 1.00mm.

Just out of inerest, was the block torque plate honed? It looks as though the top ring hasn't been sealing in the areas directly in line with the head bolt threads. I've seen similar bore scuffing to what you can see in the photo on the thrust side of the bore due to preignition.

I'm not saying that there isn't a piston problem, on the basis of one photo it wouldn't be possible. I just think it is worthwhile assessing all the evidence available before coming to a conclusion. It would be worth your while to have a failure analysis done by a third party who can give an impartial report on your engine.

If threads start popping up about the same issue with the same pistons it would be a sign that there is a piston problem but when you think about it objectively, your 6 pistons would have been part of a batch of 300 or 500 pistons machined from a forging that is more than likely used for thousands of pistons and to get 6 pistons with exactly the same fault where other sets in the batch don't have it would be highly unlikely.

It's understandable you are pretty pissed off with having to pull your engine back out because there is a problem but apportioning blame shouldn't be the first thing you do. A thread asking if anyone has had a similar problem with the same product would make sense and could be quite enlightening. An ACL product warning based on one case is probably a little premature. ACL do actually issue product warnings/recalls for parts that they have found problems with and compensate for them.

[browny]

So tonkau, you've been awefully quiet, whats the latest?

Any response to the clearance questions posed by SK and proengines?

Edited October 13, 2005 by browny

[SimonR32]

i know of 2 sr engine that have both been built with acl pistons... by seperate engine builders.

one has lost its ring lands and the other has rattled since it was built and does not seem like it is going to last very long...

[the_tonkau]

................

Edited October 21, 2005 by the_tonkau

[CRSRB25DE]

.007" is way to much clearence in my opinion.

Can you post up the spec sheet for us to see?

[T04GTR]

thats not very good.

personaly i think that any piston with 7thou aceptable clearance should be put in the bin.

they cant have that clerance.

were they mesured 90degrees from the gudon pin?

besids excess clerance wears at the bottom of the bore(when the rod is at its greatet angle.

if you pull the pistons out and its not all polished at the base of the bore then its a piston ring/machining fault.

that wear can hapen by iether detonation or forein mater(most common)

im aware that evreyone makes mistakes in the autotrade.

is it scratched up in that photo, any verticl grooves.

anyway back to the pistons, i use trust ones(os vresion) they specify .05mm(0019thou)

most yank ones are around the 3-4thou

if they are a cast piston it should have 1.5-2thou generaly.

al i can say is they are great. but i had o virtualy watch the block being bored so they were at the corect clerance. try convincing an engine builder whos been puting engines together for 20 years that that is the right clerance!! they always want to make them 3 or 4 thou.

id get the block and pistons in question mesured up elsware. to get a more acurate reading.

whats the ring gaps like? did it breath heavily?

what size is the bore, .5 or 1mm etc oversize?

basicly what im saying is that 90% of these problems go back to poor block preperation/piston instalation/cant read a micrometer/had the runs etc.

the other 10% is tuning and filtration and oil suply.

perhaps your block was water damaged and needed extra honing to remove the rust.

ive seen this alot. man picks up "good" block from the wreckers for 100 bucks but doesnt know its been sitting around for a year or so out the back.

im not sticking up for acl but this has poor block prep written all over it.

maybe they pooped up the piston install. tap tap scratch f**k get me some wet and dry!!! and a new ring compressor.

tread lightly legaly. im sure they have more money than you. and getting sued for slander isnt much fun. what if there soliciter has read this thread.

anyway i know it sux but get it mesured up corectly and get the specs on the pistons.(clerance range and ring end gaps, ring land clearnce etc) then you will have more solid ground to step on

[the_tonkau]

OK lad's, sorry for the delay. I have confirmed the piston to bore clearences. 4 thou and 1 10th as it was assembled and after running it in it was pulled down and was measured at 4 thou and 7 10ths. I initially said 7 thou instead of 4thou and "7 tenths" , my mistake . A stated early in this thread the engine builders work was never at doubt and that's why I said both they, and the acl where happy with those tolerences. We have decided to rebuild it with custom slugs with a comp of 8.5:1. 4 weeks away but worth the wait I'm sure!

[jaik]

What a shit ending to Snow White and the Six Pistons

JK

[Beer Baron]

this still doesn't explain what the problem was?

[ebola]

explanation and resolution? Lots of emotion just fizzling. So exactly what is happening now?

[R31Nismoid]

this still doesn't explain what the problem was?

Much to what i was thinking... all this hoo-haa and we are yet to hear why or what

If we dont then this thread is going bye byes

[someonestolecc]

What a shit ending to Snow White and the Six Pistons

JK

<{POST_SNAPBACK}>

From now on I'm only going to read posts by JK and have a cack

But Duncan's right we'd like to know what happened. Proengines made some good points about unlikely to be a manufacturing fault so we'd like to know what it was.

[Sydneykid]

ACL race series pistons are not forged, hence why they only handle low boost.

I should know been selling ACL parts for years.

<{POST_SNAPBACK}>

There are both forged and cast ACL Race Series Pistons available, we use the forged ones

cheers

[pt138]

There are both forged and cast ACL Race Series Pistons available, we use the forged ones

cheers

<{POST_SNAPBACK}>

:lol: Hi Tonkau, Read this string and as a few of the other members have suggested, you know very little about what you wrote on ( before your edit ). I would suggest you buy a copy of Fast Fours ( October 2005 ) and learn something about pistons first before opening ones mouth.

[R31Nismoid]

its very typical of what you see on these forums from time to time.

Ah well.

Case seems closed to me

[the_tonkau]

..........Fairly typical commments from forums users...yes.....mmmmm..... sounds like you should seek nourishment from a penis.

Waaaaah

As usual SK and a few others are trying to keep it useful. Thanks to all who had constuctive input. All parties agreeing to disagree. Custom pistons going in 3 weeks and oil gallery issues being seen to while in bits! Not giving in and looking forward to a 3 litre hybrid that doesn't rattle or spew oil out of the breathers!

Cheers

[browny]

you know very little about what you wrote on ( before your edit ).

I think I've missed something??

[GTR32]

so....what was the outcome....? (seems to be an echo in this thread)