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MCB Performance

Member Since 13 Jan 2008
Offline Last Active Mar 05 2021 10:31 AM

Posts I've Made

In Topic: Reason for engine failure

12 February 2021 - 08:30 AM

Are those pistons from the same engine !? They are VERY different designs (other than both being forgings).


The top is an Italian forging (78-26) and the bottom is also but using the Lt wt die (2115). 


WIll need more pics to help here but as one poster has already pointed out...very dry.


- Scott @ MCB

In Topic: Which brand of piston would you use in a 2006 Renegade 800

10 February 2021 - 09:40 AM

Thanks for the order (Brian?).


1 - As you can imagine, our logistics mgr. has his hands full this time of year but has still managed to keep us under 48 hrs shipping window all year! Not to mention his incredibly high standard for packaging. Your order should leave very soon.


2 - As far as break-in well... like everything else in the world it simple but complicated! I glanced at the vid Charles posted and although he outlines the need for caution his assumptions with regard to RPK and Ra are a bit too generalized for my tastes. 2-stroke hone finish is critical and ours is proprietary. For instance Plateau means nothing if your "valley" angles are broad enough to not hold oil, or what about the fact that most 2-stroke rings are chrome faced. There is very little break in wear going on with regards to those chrome ring faces, BUT you better believe if the wrong finish is on Nicasil they will NOT play well together!  Sunnen 732 (n-series) was something developed back in the day to help a chrome coarse finish accept better Ra. If your bores arent STRAIGHT AND ROUND none of this coversation matters! Lastly if you want the BEST seal then a precision lapped ring with M3 facing is the king and will seal better than ANY other but then you would need to fixture a torque plate for the cylinders.... See all those silly holes in those cylinders? Guess what happens when you bolt them all together! Guess who's cylinders stay round longer......CASE REED. There is SO much more here to discuss its really out of the range of anything but a full blown 2 day class and thats just on ring seal. 


3 - No one is talking about breaking in a crankshaft and ITS needs. THATS what needs the additional oil folks. People that slather pistons during assembly are just kidding themselves.


4 - To make it simple the testing has been done and regardless of the Industry the consensus and data all points to the same break in procedure: increasing load over increasing time (this assumes all the other parameters are controlled by the way)


5 - Daag - Thanks for the shout out, I spend a large portion of every day helping folks and when their ears are open and their capabilities match, they are usually very successful.


- Scott @ MCB

In Topic: Which brand of piston would you use in a 2006 Renegade 800

09 February 2021 - 02:26 PM

Honestly? I don't recommend using any crankshaft that has been exposed to coolant as it is a fairly rapid reaction and generally due to its surfactant nature once its in there, its in there. Same goes for catastrophic top end failure, its not uncommon for that debris to migrate into the rods and mains and not be seen with the naked eye. 


I had one customer that had a major coolant leak tell me he was "back in" with no tow and it was eating so much coolant he didn't think he was going to make it back to the cottage. He made it, said temps didnt really spike too badly, disassembled the engine that evening and observed ALL the bearings were all destroyed and had a "bound" feel to them all. I asked if there was any prior coolant usage and he said unequivocally no.  This was a 2000ish mile original owner 800 Etec. Is it the same as simply splashing some downstairs vs running it? Maybe not, but why do you think ALL the mfr's caution you to drain AND evacuate the cylinders when performing a top-end service....


That being said, lets say you have a known good crank assembly with very low miles etc etc, In that case if cost is an issue and you want to try and reuse a potentially contaminated crankshaft remove it from the cases and CAREFULLY flush the non-sealed bearings with a very light weight oil (ie - WD40) or petroleum based solvent. You will likely never get out all that is embedded and the additional danger is flushing it into the inner seal areas, but it may give you some piece of mind.


Lastly remember to NEVER use compressed air on roller bearings.


- Scott @ MCB 

In Topic: Which brand of piston would you use in a 2006 Renegade 800

08 February 2021 - 09:06 AM

Please try to limit any roller bearings exposure to any type of glycol (Ethylene or Propylene). It is highly corrosive in that situation and can quickly lead to bearing failure. Further the silica content can spall the bearings when operating temps are reached. 


Oh and by the MCB has lots of piston and crankshaft choices and I hear they are pretty decent guys..... ;)


- Scott @ that place

In Topic: Recommended ring end gap

31 December 2020 - 11:37 AM

The reason for a mfr. giving a range of acceptable ring gaps is three fold.


1 - Accommodate production tolerances (remember the gap changes as a funtion of Pi)


2 - Accommodate wear and increase "serviceability" (see Pi above)


3 - Let the consumer know that the dimension is very "flexible"


In the real world the ideal gap is dependent and calculated from multiple influences (i.e. Ring material,  Ring temps, intended usage, boost, etc.)  Tailoring this dimension has direct benefits on durability and life expectancy.


There are lots of "rules of thumb" with rings and many are just simply lore or based on 4-stroke environments. But the one I've told for more years than some of you have been alive is.... Too much ring gap and no-one will ever know, too little ring gap and everyone is going to know.


That being said and relating to the OP, .008 is too tight and .024 is too loose. Also setting the second ring 10% smaller in a dual ring application that has properly cut ring lands has several benefits. 


Heck filing rings alone is a 2 hr dissertation.


Happy New Year !   -   Scott @ MCB Performance