Hey everyone, I'm new to this forum and really the ATV scene in general.

I just bought what I thought to be a cherry/mint 2007 YFZ450 about 3 weeks ago. First thing I did was change the oil and the plugs and gave it a good once over. It sounded great and appeared to run fine. The guy I bought it from said to make a list of parts and he will think about splitting it with me since I literally got 10 minutes out of this quad!

I took the quad to ocotillo last weekend. After 10 minutes it quit running and wouldnt idle. Trailered it home and tore it apart last night to find cylinder wall scoring, smudged/melted metal on the piston, melted/deformed ingition coil, blued and scored cam, and scored cam bearing journals. It's not major damage and I don't think that there is bottom end damage.

I plan on doing all the work myself with the assistance of my father in law who has been a mechanic for years. I really want to avoid buying a whole top end if I can.

MOST IMPORTANTLY, what caused this to happen in the first place. I don't want to spend a bunch of $$$ just to have it happen again!

What do you think about this Namura piston kit: Namura Piston on eBay

What do I do about the blued/scored cam?

Are the cam covers salvageable?

Do you think I'll be able to hone the cylinder?

If not, what do you think about this big bore setup: Big Bore on eBay

Finally, if I do go with a big bore kit, what other mods do I have to do to the bike? Jetting?

Thank you all so much! I look forward to your advice.

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The cam cover looks like it was run dry. How was the oil when you changed it? Really bad or brand new like the guy put fresh oil in and sold it. I would say replace both cams and the covers. Is that orange RTV silicone on the gaskets?

I'm no expert but it looks like someone has been in that thing already.

Sadly... I agree.

The oil wasn't overly dirty but it wasn't fresh either. There was no obvious metal in the oil or the filter.

Any other advice?

Iv only had one of these apart but I never remember orange on the stock gasket. How does the rod feel? Wrist pin? Maybe a oil line got pluged.

looks to be opened up before too

Lack of oil up top.

That motor has seen some HARD miles...

I would say a few things to think of.
1) Oil, Either lack of oil getting to motor or cheep/wrong kind of oil was used.
2) Jetting to lean.

In all I would say with this much wrong in the top end you would be best served going through the bottom end at the same time. Check shims to see where valves are along with the seats. Sorry to say but I would look at all parts before reassembly. It would suck to spend that kind of money just to have it come apart and take out the things you just fixed.

X2
The cylinder has been off for sure. that is not stock gasket materiel.

x3 already opened up for sure. I would document all of this and also maybe take it into a shop to have it professionally evaluated in case you need to try and go after this person for compensation. Did they say it's a stock engine? And never been gone through? Also does the engine case numbers match the numbers on the title?

I was thinking that it may have been run lean and not jetted properly. It has the stock muffler/exhaust with the baffle removed. Would that cause it to run lean enough to do this damage?

I don't think it was jetting issues, more like lubrication issues.. The cam shafts look like they were starved for oil, they look bluish in color which means they were hot. I would send Morgan here a PM and see what he says, he seems to be the engine guru around here for the quad stuff.

Yamabond is grey, not orange.

It appears an oil issue.

dang....you cant even see the crosshatching in the cylinder walls anymore....i'd say sleeve it too while its open...you don't know if its been honed before...

I've never seen damage on a coil like that either. I am going along with lack of oil. Have you changed the oil on a dry sump bike before? Have you read the manual on draining and filling this bike?

Is it an '07, or an '06 purchased in '07? If an '06, look into this oiling situation.

http://www.jtatv.com/ProductDetails.asp?ProductCode=OU-100

the '07 has the oil mod


I just took my top end apart to replace a head gasket with the help of 'The Fog'

From looking at those pics there is some definite lube problems. Those cams got HOT, the cylinder is toast, and I would not trust the bottom end, take it all apart and start over.

Did you buy this from a guy in Fallbrook? $3400?

I recommend factory parts only. Just my .02

Yes-What do you know?

Yes and Yes. I kinda noticed but didn't pay much attention to the coil when I changed the plug, so I believe that these issues existed prior to me owning it.

How do I cross the engine number to the VIN number to see if its a match? Or is the VIN number on the motor too??

I remembered you came on recently and said you bought an 07 YFZ for $3400. I was in talks with this guy to buy this quad. I thought about it for a few days and when I called back to go get it it was sold the day before.

The title of the ad was this: 2007 Yamaha YFZ 450 """IMMACULATE""" - $3400 (Fallbrook)

The guy is an auto dealer in San Diego and also owns an Auto Repair shop. I do not know what recourse you have but I would pressure him hard to pay for AT LEAST HALF! He put the word "Immaculate" in his title which does not exactly describe the bike.

I know in my line of work if you make any sort of statement such as "Immaculate" or "Perfect" or "great" condition, you are liable for your statements should they not be true.

I'm sorry to hear about your dilemma. I went back through my emails to see if he made any statements as to the condition and he didn't, we only talked price.

The cam tops should be dripping with oil when pulled apart, I don't see a lick of oil at all. Did you changed the oil filter? It looks like oil is not getting up there. It was definitely reassembled, maybe no assembly lube was used. I would look into buying a new OEM cylinder rather than resleeving, just as cheap. Also, pull it apart and re do the crank. something isn't quite right.

Another thought, are you sure you put the oil filter in the right way? If you put it in backwards, it will starve the motor for oil. Just throwing that out there just in case.

Yikes not good. If the guy you bought it from was in the car business its 99% more then likely an auction bike. These bikes are bought for a dime a dozen at auctions and anyone can make them look good.

For sure lack of oil. When reassembled the cams caps were not torqued in sequence and were done WAY to tight, and the cams lock up and gal.

My advice, track down the seller, and show him. You are looking at a pretty penny to fix it right. The head and cam caps with need to be line honed, new crank, new cams, new cylinder (re-nikasil that one or buy new OEM, Im not a fan of sleeved cylinders for longevity), new piston, etc etc. If I had to guess I would say in excess of 2 grand

Unfortunately the YFZ head and cam caps are machined together as one so they need to stay together and be fixed. Dont mix and match new caps on your current head.

What kind of oil did you use on this when you changed it? Also what you may no know is if you remove the oil return line on the bottom of the oil tank there is a screen filter. this is something that should be checked. Because of all the silicone used to put this bike back together this filter may have gotten clogged and thus starved the engine. Just something to check. I check mine every other oil change.

I wasn't aware the filter was directional, could you please elaborate? I know the cap has a V to align the filter apon re-assembly.

Failed cam mod?
far as putting an oil filter backwards on these would seriously require a hammer.
the cylinder could be just hours of use and lack of changing your oil or air filter regularly. definitly some sand in them sidewalls. getting color like that in a piston isn't good. Also a fan of factory parts unless its a piston. even then aftermarket doesnt always get it right. As for the coil, thats bad but common. the coils on the 450's like to pop up and if not pushed in correctly against the spark plug what you basically get is an arch spark thus melting the coil. go on yfzcentral and someone should have a coil for you cheap. I use a rubber stopper glued onto it ( I run am IMS desert tank so less clearance. )

What do you mean by less clearance due to the IMS tank?

hE MEANS THE BOTTOM OF THE TANK IS CLOSER TO THE HEAD THAN A STOCK TANK WOULD BE.

I have visually inspected the crank and felt for excessive play and/bearing seizure and don't see any indication of damage. Obviously I have a dilema here.... Spend the money and be safe, or jew out and risk it. I guess as long as its open I should just do it and be safe...

What do you all think about the HotRods replacement crank that comes with bearings etc, for like $220?

What about the CylinderWorks 98mm big bore cylinder, piston, rings, and gaskets for $400. OR should I do a stock cylinder/bore and a Namura teflon coated piston?

And finally, how about the HotCams Stage 3 cams for like $300?


I truly appreciate everyones advice. Thanks!

I like a good running stock bore personally. Morgan's comments above are 150% correct.

I have heard of too many CW cylinders cracking. I would not use one. Replace the crank, OEM or send yours to Crankworks to get rebuilt.

I'm not positive on the Yamaha Quad if they are directional, but on other bikes they are. Just making sure

thats bs. Thats a clean 2 grand if you take it to someone......that guy should cover more then half....especialy if the engine has been apart.

its not a huge deal if a engine blows up and the guy offers to fix it, or if it says that it has issues but "immaculate" is bs.

i sold a 85 i did a top end on, blew up a week later, but i took it back and did a top to bottom rebuild on it. Turns out i didnt gap the rings right.......I eat poo happens but not paying for it/making it right is just low life scum/bs


good luck

The Problem I see here is- you bought the quad, took it home, changed the oil and filter.
If the seller finds this out, you 2 go to court. I would think it would be easy for him to say something
along the line of "maybe you forgot to put the oil back in".
My guess is it had more wear and tear than he thought.

I have to agree with Morgan on this one. If I was the seller I would say you did something wrong when you did the oil change and in court, you would have to prove otherwise.

F it... I'm buying a new stock cylinder ($214), piston & rings ($120), gaskets ($40), etc, cleaning up the cam and bearings, used coil ($20) and calling it a day.

The crank is FINE. The cylinder and piston didnt seize. The cam got a little tight and was enough to stop the engine at idle. With throttle it would run. If I let it cool, it would start and run for 5 minutes on its own. One of the cam cap bolts was almost stripped so I'll helicoil ($50) it. My guess is that the cam bearing was over tight. There WAS oil pooled when I pulled the cover off.

The cylinder/piston damage is just incidental to a motor that probably has been run hard and may have seen some sand in the past, but I am confident that is not what CAUSED my problem. I am glad I caught it now!

I will definetly flush the oil passages and check the oil pickup screen to ensure none of the ghetto silicone came loose.

Thank you all for the advice!

Steve

if you need torque specs let me know. I have them all. i think its 7 NM or something very little for those cam journals in a chris cross pattern. head bolts take a certain procedure as well. like 60NM back off then 20 NM then 90 degree angle torque. dont take those as exact specs but close. thinking off the top of my head. Checkout ordering parts from www.flatoutmotorcycles.com pretty cheap prices. $214 isnt a bad price for a cylinder either.

Thanks! I actually downloaded the service manual from here: http://students.washington.edu/yfz450/yfz450/
So I have all the torque specs and will definetly follow them religiously!

I had a "Shocking" epiphany tonight... FIXED it!!!!!!!!

The cam bearings and cams were seizing from being over tightened and was definetely the problem here. I followed the manual for ignition sytem diagnostics and luckily I actually have another 2007 YFZ450 that I used parts form to eliminate the CDI unit, Coil, etc. before ripping into the motor.

Ok so I rebuilt the top end and cleaned up the cams and cam bearings, ensured proper torque on everything. As part of my mini overhaul, I used my dremel to clean up the melted plastic on the coil becasue it seemed as if it wasnt letting it seat correctly. No sweat... Adjusted the valve clearance and fired her up...

Sure enough it didnt run for CRAP! Spitting and sputtering and dying with any throttle. WTF. I have been chasing my tail for days now. The cams are smooth, the piston and cylinder are smooth, the engine cranks perfect but wont run... Hmm

Ok so Monday I completely disassembe the carb, inspect, clean and reassemble (which has not been rejetted or needled - STOCK). Still runs like (_|_)... At this point Im really getting frustrated.

We couldn’t figure this heap o junk out for anything right… Kinda suspected the pickup coil but the resistance checked out OK. So I decide tonight to see if there is a consistent spark at the plug. I pull the plug and coil out and touch the plug to the frame and hit the starter. I shocked the I eat poo out of myself. I was like WTF? So I layed the coil on the frame and examine spark without me touching—Spark looks good. Hmmm.

So I decide to look in the spark plug hole, crank it, and give it gas to see if gas is entering the cylinder which it was, but oddly enough I hear the sound of an electrical arc… Weird since the spark plug isn’t even in the coil right?.?. Well the coil was laying on the frame…

Check out the tiny pinhole in the picture. It is causing the coil to short out and not provide enough spark to the plug!!! I throw some electrical tape around it, put it together and IT RUNS GREAT! HAHA what a stroke of luck!

Oh and guess what, I have a new coil in the mail and it should be here tomorrow or Friday! Looks like I’ll make it to the desert this weekend afterall!! Totally stoked!

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Wow , sometimes its the small things that drives us crazy. Good luck.....

if you ever need parts or advice on the yfz try YFZTECH there is alot of yfz gurus on there and most those guys drag so they have aton of oem parts
heres a link to check it out http://www.yfztech.com/