I have an 05 YFZ and the motor is giving signs that it worn out. Im thinking of getting a big bore kit since its going to be taken apart but who should I go with and what kit. Who can build it in So Cal. Thanks

714-892-1300

depends on how much you want to spend. there are sooooo many options you can do. many shops in so-cal can do the work for you. its better you do it before it blows. much cheaper. recommend you split cases and replace crank bearings at least and get all the parts inspected.

Well, if I split the cases...i wanna make it a 480-500cc. Its an Alba bike so it has every bolt-on on it that they sold at the time. Its my wife's bike so I imagine the engine isnt in too bad shape but she does drag it. Do you suggest certain brands to purchase for the big bore kit though?

you might want to give mmad in east county san diego a call they know 450s very well.

What part of So Cal are you in? If you are around San Diego, I would tell you to go see Allen Fox of Fox Engine Works. One of the best, if not the best, off-road bike mechanics in San Diego County. He's located in Alpine. 619-445-1415.

if its an 05, id look into keeping the stock cylinder and putting an 06 and later crank. make it a true 450. if you do want to go bigger, Id just do a bore/replate to freshin the cylinder. problem with big bores are thinner cylinder walls to keep em cool plus the pistons have tiny skirts so the piston has more possble walking.Ive read on other site of big bores haveing clearance problems. add an 2007 and later outer side case and oil pump for the oil mod. Im sure any of the repair shops should set you up. being down south and the racing I do, Id talk to Duncan racing. If your more OC or LA, call CT racing. calling those two shops should point you in the direction you want. they will tell you what works well, and what lasts. they have done the experimenting and tested many engine combinations. they both know what works.

Big bore is a great idea once you have exhausted compression or stroke. However, those should come first. If you don't mind buying race gas, go higher compression. If you don't want to buy race gas, stroke it. Either way be sure to tear it down, and at least replace the crank bearings. If you want to PM me with a budget I can help you pick the parts.

Let me help you GWTT. The bore size has nothing to do with the length of the piston skirt. The piston pin placement dictates that mostly. As for the piston "walking", I think you are referring to piston slap, or the piston rocking back and forth as it moves through the bore. The YFZ engine does this irreguardless of bore size because all of the pistons have short skirts. Very similiar to an LS1 in that aspect actually.

Now, as far as the oil mod, the 07 mod is the wrong choice for this application. If the OP runs a larger piston, or a stroker crank the piston will contact the oil squirter. You can clearance the piston, or the oil squirter to make it work, but why? The better idea is to get the older style oil mod done, and just run the updated oil pump.

I use race gas now (108) on all my bikes. I want a complete tear down, I dont want to half (_|_) anything. ive been eyeing the Venom ATV cylinder and piston replacement (12:5 comp). Anyone hear of Gils racing in Rancho Cucamonga (sp?). I wont deal with allen fox...did once and it wasnt a pleasant experience.

I would definetly not use race gas on any modern 4 stroke with less that 12:1 compression. All you are doing is robbing power. However, if you are already using race gas on that bike you might as well bump the compression to make use of it. I would go to a 13-14:1 compression ratio. Stick with a stock bore piston. If you still want to spend $, drop $250 on a hotrods crank fr a little more stroke and you will have a great running bike.

I dont do big bores but thats what I was refering to in the clearance issues. as far as the slap thats also what i was trying to describe. im not the best teacher but I do understand it.for racing hot rods crank, 13:1 or 13:5.1 i didnt know a difference. mild port with stock cams, fuel customs intake and a restricted slip on (for d/b levels) makes alot of power. to where Im running with 525cc ktm's on the start and passin on the up hill sections, put a better flowing exhaust some cams and you'l have a screamer of a 450.

Decided to go with Trinity's 470 kit...............................

Garrett @ Fuel Customs in Pomona does great work and has done all my bikes.

Big engines blow up.

so do small ones... they try harder

Why don't you just sell the 450 and buy a stock honda 400 ex... those bike NEVER break! ahahha

We know, we know, your stock (_|_) Banshee never blows up. Oh wait, that's because you never go to the damn desert.

If you haven't already found someone to rebuild it or even if you have, hit up my shop RND Motorsports. Rich the owner knows YFZ's like no one else, he also has a totally done up 05' and enough parts to build 2 more of them. We have done many performance builds and our Desert race team Chakas Racing just took 2nd place in the Baja 500. We never half-(_|_) anything if there are ever any problems we give it to you straight, no bull. We have the lowest labor rate anywhere $45/hour and very experienced technicians.

RND Motorsports, 1405 Morena Blvd. San Diego, CA 92110 (619)276-7263

wow didnt know u guys were on here. i have had these guys do a couple things on my raptor and was very happy with the work!

I'm just the intern/advertising commitee, but if anyone needs to contact RND Motorsports feel free to do it through me also.

The pro shop

http://www.proshopmotors.com/