2012 Apex motor build

[machzrobbie]

Well after taking a few of the newer Apex motors apart - every one that has had some decent boost to it has had cracked pistons. I decided its time I took mine apart and inspect it and build it a bit stronger. Sure enough all my pistons had cracks in the skirts, on was right up to the bottom side of the piston. I decided a while back after building a couple of motors with aftermarket pistons that burnt oil that I wanted to stick with yamaha rings, so I talked to Dave at Hurricane about building a piston that could use oem rings. Below are the pistons.

 

[machzrobbie]

After measuring the block,I found that cylinder # 4 was pretty ovoaled, so new block is on its way. Plan is to drill and tap new block for long head studs, and install new rods and pistons.

 

[sledracer]

How hard were you pushing the original motor with stock yami pistons?

 

[machzrobbie]

pump gas most miles at 12-14 pounds - motor has been raced at 19 lbs on race gas for one summer and the odd timein the winter

 

[mbarryracing]

Robbie,
Do you think you cracked the skirts on the stock pistons trail riding or when you wicked it up for asphalt?
What CR are your new pistons?

 

[machzrobbie]

Robbie,
Do you think you cracked the skirts on the stock pistons trail riding or when you wicked it up for asphalt?
What CR are your new pistons?

Probably is, but the motor out of my 06, and stone's motors out of the older apex's took more abuse then this one with the older style pistons and none of those pistons cracked. All of the new style pistons I've removed have had cracks in the same place and one of stone's 2011 motors had a failure which I believe may have been a piston breaking. Dave made to new pistons at 10:1 - I/m going to install 2 head gaskets to get me back down to 9

 

[rxrider]

Oh pretty cool piston
and not soo cool piston in the last pic.

 

[machzrobbie]

Pictures of block with long head studs

 

[machzrobbie]

Got the motor back together today and started installing it back in the sled - I wanted to get it together today so I forgot to take more pictures. I want to thank Dave from Hurricane for supplying the parts and advice on the package and getting the pistons made. Really looking forward to seeing how the package works!

 

[machzrobbie]

Sleds together and running, going to try and get it out for a ride tomorrow!!

 

[kviper]

Hi Rob! Do you think the crack's came from bad fuel on the trail or from high cylinder pressure/ high boost? Deto censor may have stoped detonation but would have done nothing for extream load from high boost?
Have you had any strictly low boost 5-7 LB motor's apart and if so was there any sign of crack's?
Thanks, Kevin

 

[kviper]

Would have also been interesting to see what change there would have been after some more mile's? Maybe not much?

 

[wantboost]

So can you buy new blocks from yamaha?

 

[machzrobbie]

My personal opinion on the pistons is the new generation are not as strong as the 06-10. If you look at the skirt they are just a bit thinner, and I think if someone plans to push the boost that they should be changed. I have taken a non boosted motor( 6000 miles )apart to install rods before the turbo install and the pistons were fine, so it is definatly stress from higher boost. If you plan on trail riding with low to moderate boost you may be ok - i know there's one running around with higher mileage that's been boosted all its life.

Yes new blocks are available from yamaha, but they are not cheap! Another option is to re plate them if they aren't too bad

 

[kviper]

So I shouldn't have any issue's at 5-7 LB.