T-u-R-b-O Posted August 22, 2006 Share Posted August 22, 2006 Hi guys, I recently purchased race pistons from MAHLE designed for hard abuse on the RB25DET... i took standard bore pistons and slightly honed the block... at first when I received the pistons they seemed very good and the pistons rings are amazlingly strong... they also have some special coating on them... Now the bad points: 1) Due to them being race pistons, they are not fully round... dont know the right english term for it, but their surface on the side only has around 50% contact with the cylinder wall, which means that when pistons and oil are cold, that they have an extreme knock since they "tilt" from left to right... 2) thanks god that I installed the first piston as a test and spun the crankshaft to check all clearances... what happened? the MAHLE pistons do not have a housing for our stock RB25 oil squirters and mine broke off... this seemed kind of strange to me, since the pistons itself is designed to support the oilsquirters... so i had to replace the broken one and really customize the other squirters and the pistons themselves in order to make both fit in the block... very time consuming and unnecessary work for pistons which where build to go into the RB25... everything fitted, checked the clearances and started the engine (hopefully leaving the oil squirters alive)... very loud "tack tack tack" noise from the pistons... lets the engine run for 30min to get the right temperature... once oil temp passed 80degrees, the knock from the piston reduced quite a bit... after 500 KM of hard driving, the compression is straight 10 across the board so the pistons seem to be doing their job... well, hope this could be of some help, and i suggest that you go with wisecos or something like that, cause otherwise you will have to do quite a bit of fusing around to make the Mahle pistons work... Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/ Share on other sites More sharing options...
Amaru Posted August 22, 2006 Share Posted August 22, 2006 Thats exactly what you get for buying a high grade forged piston. The strength is determined by the silica content which expands with heat. The pistons are ovalled so when they expand they become a perfect circle. If they were this shape when cold they would not work at high temperatures once expanded (they would jam in the bore because they would physically become to big). Its not a problem, its something you have to live with when using high quality forged pistons. Arias are exactly the same. As for the oil squirter, had the exact same problem with Arias pistons. Machined a little off the oil squirters and they cleared it fine. Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2430924 Share on other sites More sharing options...
Mik Posted August 23, 2006 Share Posted August 23, 2006 The skirts on Mahle pistons are too short for street use in my opinion Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2431049 Share on other sites More sharing options...
R31Nismoid Posted August 23, 2006 Share Posted August 23, 2006 I think Amaru has hit the nail on the head. I find it funny too, saying "use wiseco instead" when your probably going to see the same thing. Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2431940 Share on other sites More sharing options...
T04GTR Posted August 23, 2006 Share Posted August 23, 2006 ok, what is the recomended piston to bore clearance for these pistons. bearing in mind that a "good" un damaged stock bore will have around 3-4thou clearance. honing gives you another 1-2 thou on top. so you could have up to 6thou clearance or more. in regard to the oil squirter issue. thats more a suplier fault. as the recess clearly wasnt milled into them. i know some american and european parts arnt a true fit. i tend to stick to the sulpiers who "specalise" in theses engines. if i was going to build up a chev i wouldnt go to tomei and ask them to make me some pistons lol, id go je or a american product. etc etc the reason they rattle is because of the high silicon content. BUT this often isnt the best way to go. that is why american pistons are rattely,and these obviously. jap pistons are superior in there design and metalergy and often have the same silicon content but requir only half the clearance. and dont rattle typical clearances for say. a JE piston is around 4 thou. for a trust/grex/os piston are 1.9thou wich is a factory clearance. and why they are twice as expencive. mahle pistons afre very good. they were good enough for the 1450hp turbo 1.5 liter bmw f1 engines all pistons are barel shaped when cold. just make sure yor clearances are ok. otherwise it will breathe to much. mesured at 90degrees fron the gudion pin hope that is of some help Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2432855 Share on other sites More sharing options...
T-u-R-b-O Posted August 23, 2006 Author Share Posted August 23, 2006 i am aware of the clearance fact and that this is why the pistons can knock while cold... the stupid thing is that I didnt even get one of those data sheets with the pistons which states the clearance etc... we recently put together a SR20det in our workshop with Arias pistons which require 0.1 clearance which is alot... on my engine i have stock bore, and the clearance after honing was max 0.03 at the last cylinder... the others had 0.01 - 0.02... i also said to get wisecos because i have seem them fit on the little brother from the RB25 (the CA) and I had no issues with clearning or high knock... i just bolted them in, and worked perfectly... CA18 also has identical oil squirters as the RB25... a question... could somebody tell me how i can tune my engine now, because i am hitting amazingly high knock readings (255 and up) with these pistons? Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2432885 Share on other sites More sharing options...
rob82 Posted August 23, 2006 Share Posted August 23, 2006 i am aware of the clearance fact and that this is why the pistons can knock while cold... the stupid thing is that I didnt even get one of those data sheets with the pistons which states the clearance etc... we recently put together a SR20det in our workshop with Arias pistons which require 0.1 clearance which is alot... on my engine i have stock bore, and the clearance after honing was max 0.03 at the last cylinder... the others had 0.01 - 0.02... i also said to get wisecos because i have seem them fit on the little brother from the RB25 (the CA) and I had no issues with clearning or high knock... i just bolted them in, and worked perfectly... CA18 also has identical oil squirters as the RB25... a question... could somebody tell me how i can tune my engine now, because i am hitting amazingly high knock readings (255 and up) with these pistons? I dont know the old fashion way of just listening to the motor to detect knock!! Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2432950 Share on other sites More sharing options...
Risking Posted August 23, 2006 Share Posted August 23, 2006 I would not let you anywhere near my engines after reading the above posts! 500Km's of hard driving on a fresh engine?? Also when your assembling such an engine you should have been aware of the side effects to using such products. Id also have to agree with TO4GTR in saying with a jap engine generally the Japanese have them alot more wired than the americas. Pistons are not going to effect your Knock readings unless you have changed the CR?? If the piston to bores are that bad it could be the knock sensor picking up piston slap! Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2433568 Share on other sites More sharing options...
R31Nismoid Posted August 23, 2006 Share Posted August 23, 2006 nothing wrong with driving it hard on a fresh motor. what are the reasons it cant be done? Once the rings a bed, there isnt a whole lot more too it Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2433580 Share on other sites More sharing options...
Risking Posted August 23, 2006 Share Posted August 23, 2006 Dont get me wrong, I agree with you, once the rings are bedded and its been checked over it "should" be sweet. However when you have an engine that rattles and has been built like this Id personally tread carefully for a bit longer even if you are 500% sure its piston slap. Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2433613 Share on other sites More sharing options...
T-u-R-b-O Posted August 23, 2006 Author Share Posted August 23, 2006 I would not let you anywhere near my engines after reading the above posts!500Km's of hard driving on a fresh engine?? Also when your assembling such an engine you should have been aware of the side effects to using such products. Id also have to agree with TO4GTR in saying with a jap engine generally the Japanese have them alot more wired than the americas. Pistons are not going to effect your Knock readings unless you have changed the CR?? If the piston to bores are that bad it could be the knock sensor picking up piston slap! i honestly couldnt care less whether you will let me near one of your engines... be aware of side effects of using such products?? for example that pistons made for my engine breaking off factory oil squirters?? also, i could care less for such unnesseccary comments like yours, since i was trying to prevent people from building them it and breaking of all oil squirters... and not to discuss whether mister superman will let me near of his precious engines... Nico ps: there is absolutley nothing wrong with driving a fresh engine hard from the start... i drove ~100km normal, and then build my way up to the serious HP... all down to ~500km... Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2433938 Share on other sites More sharing options...
r33_racer Posted August 23, 2006 Share Posted August 23, 2006 yeh alot of race teams...drags, circuit racing and even f1 i think dont bed an engine in for 1000ks before using the motor. They do like a half hour test of running it through the rev range and away they go. Saw something on fox about a f1 team bedding their motor in after assembly and they just had it on an engine dyno and for about 15 mins it just went through different parts of the rev range screaming its head off and that was it...they said it was good to go into the motor for any further tuning and then off to race. Its not like its a big deal to do a set of rings in a competition/worked motor for reliable and consistent power. We didnt do a proper bed in in the rb30det...about an hour of free rev range running, change oil and did it again and then bam to the track for thrashing Piston slap will show up on the knock sensors....the piston goes through the same motion as it would with pre ignition, its knocking itself against the bore, except its doing it on its own cause of sloppy clearances. Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2433962 Share on other sites More sharing options...
Swiper the Fox Posted August 23, 2006 Share Posted August 23, 2006 for greater oil squirter clearance....place the correct sized copper washer under it (between squirter and block) for extra clearance (Aries pistons require this mod) Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2433978 Share on other sites More sharing options...
Muz Posted August 23, 2006 Share Posted August 23, 2006 Sorry everyone but I just have to ask a silly question. Tomei are recognised as a leader in RB engine hardware, was the only reason for not using them cost? cheers Muz Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2434064 Share on other sites More sharing options...
r33_racer Posted August 23, 2006 Share Posted August 23, 2006 Sorry everyone but I just have to ask a silly question. Tomei are recognised as a leader in RB engine hardware, was the only reason for not using them cost?cheers Muz how are they a recognised leader in engine hardware? How are their pistons so much greater then say ACL, CP, Arias, JE, Mahle(with acl) and everyone else? If you can make 1000hp using CP pistons that might cost you $1500 or 1000hp using tomei pistons which might cost you twice as much(honestly dont know but im guessing they are not cheap) what does it really matter? Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2434223 Share on other sites More sharing options...
Mik Posted August 23, 2006 Share Posted August 23, 2006 how are they a recognised leader in engine hardware? How are their pistons so much greater then say ACL, CP, Arias, JE, Mahle(with acl) and everyone else? If you can make 1000hp using CP pistons that might cost you $1500 or 1000hp using tomei pistons which might cost you twice as much(honestly dont know but im guessing they are not cheap) what does it really matter? Have a look at the price of Tomei pistons...not that much more than say CP's or JE's. And the advantage (for a street car anyway) is the ability to run 0.002" clearance...so they don't rattle Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2434283 Share on other sites More sharing options...
r33_racer Posted August 24, 2006 Share Posted August 24, 2006 (edited) I ran .002" clearance on my cp's in the rb30det. And I know cp's are in the country and a days freight away, and quite a few companies all stock them now. Tomei you could have to wait for a shipment from Japan, and that can always vary as has been my experience with parts from Japan, unless ofcourse someone is stocking them. Edited August 24, 2006 by r33_racer Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2435210 Share on other sites More sharing options...
T-u-R-b-O Posted August 24, 2006 Author Share Posted August 24, 2006 for greater oil squirter clearance....place the correct sized copper washer under it (between squirter and block) for extra clearance (Aries pistons require this mod) i also thought about doing this, but then the squirters would hit the crank... would be great if the exact copper washers would get supplied with the pistons... Nico Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2438037 Share on other sites More sharing options...
B-Man Posted August 24, 2006 Share Posted August 24, 2006 Its not a problem, its something you have to live with when using high quality forged pistons. Arias are exactly the same. I never had any slap with my Arias Pistons - I think the clearances have to be 100% spec'd as per Arias recomendation to avoid this - also use the rings that come with the pistons - not gapless rings or anything for these. Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2438102 Share on other sites More sharing options...
Mik Posted August 25, 2006 Share Posted August 25, 2006 i also thought about doing this, but then the squirters would hit the crank... would be great if the exact copper washers would get supplied with the pistons... Nico You can space them about 2mm and still have plenty of crank clearance... Link to comment https://www.sau.com.au/forums/topic/131389-attention-forged-mahle-pistons/#findComment-2438442 Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now