YFZ Central banner
1 - 9 of 9 Posts

·
Registered
Joined
·
14 Posts
Discussion Starter · #1 ·
Hi all!

New to the forum, and I love the abundance of information on the site. I recently purchased a 2006 YFZ450 (Special Edition-50th anniversary). The quad has a Hot Rods stroker kit as well as a 98mm Big Bore up to 501cc, along with HMF Comp Exhaust and jetted fairly rich. There is about 5-6 hours on the rebuild and such and it is running fine, but happened to blow the head gasket (boo!)

I am replacing the head gaket with a cometics 98mm, and KMS Performance Stud Kit instead of OEM head bolts. Everything has been measured and nothing is warped, it seems the gasket that came with the kit just didnt hold up very well or someone didnt break it in properly...

My question is what would be proper procedure regarding the break-in time or methods to have the best luck with the new H.G? Like riding patterns, certain amount of time before going full throttle on it, etc.
Thanks for any feedback all. 8)
 

·
Registered
Joined
·
592 Posts
Welcome to the forum! Sounds like a nice build, but I'd be weary of the Hot Rod's stroker though... Culprit of a lot of failed builds. Also heard they are hit or miss, so you may be ok.
 

·
Registered
Joined
·
124 Posts
Regarding the break-in, I bring the new motor up to 150 then cool it down. Bring it up to 200 then cool and bring it up to 210 and cool it before busting out WOT. Regarding the YFZ head studs, you will have to install the two on the inside up-side-down so before you put the motor together use a cutting wheel or metal cutting saw and cut a notch on the ends of those two studs to accommodate a standard screw driver. You will be thankful you did whenever you have to remove the head with motor in frame. Good luck.
 

·
Banned
Joined
·
1,160 Posts
Hot rods head gaskets are known to be not that great. I'm rebuilding my motor right now. Bought a hot rods bottom end kit will all the gaskets. I used an OEM Yamaha head gasket instead of the hot rods.
 

·
Registered
Joined
·
9 Posts
Here are 2 issues I have had in the past related to failed head/base gaskets... 01 raptor 660 blown head gasket. raptor and yfz450 both use a MLS (multi-layer steel) head gasket. MLS head gaskets require a very smooth surface to seal properly. any machining (flycutter or the like) marks that can be seen or felt on the sealing surface of the head or cyl will cause a gasket failure (I'll comment on the fix for this later if this is your issue).
Issue 2, 06 yz450 new top/bottom end rebuild with hot rods crank kit and gaskets. Hot rods base gasket is paper and OE is a MLS gasket. problem... there is an oil passage between the cyl base gasket and the case. This oil, over about a season of riding, will soften the base gasket, causing a clog and catastrophic engine failure. My advice, use a MLS base and head gasket.
My break in procedure is similar to 660's, with a little less precision on temp. The big thing during break in (imo) is heat cycles. I start the engine and let it run at a slightly higher than normal idle until the cylinder(not the head) cannot be touched for more than a second with a bare hand. Shut off the engine and let the entire engine cool to ambient(room) temp. Repeat this process once or twice a day for 3-5 days. This hot/cold cycle helps all the dissimilar metals find their "home". I change oil and filter after break in. After break in I normally take a 15-30min ride at 1/2 throttle or less. From there if it has not shown any signs of issues, I let it have it. I have been a professional auto/truck mechanic for 20+ years and have built several 2 and 4 stroke atv/mc engines using this process and I have yet to have a failure due to break in. just my .02
 
1 - 9 of 9 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top