2018 YZ450F Engine Rebuild

[M5-]

So I thought I would take the opportunity to let guys know what I'm finding inside my 165+ hour YZ motor. It may have as many as 170 but whatever you get the point. At the end of last season I lost second gear and ended up riding my "B" ride for the remainder of the season. As expected the cog gears for second are worn and rounded off. As well the shift fork is bent by .5mm and twisted. It also has some pretty good wear on it. The remainder of the cog gears all look fine even though Yamaha changed them all for 2020. The cheapest repair would be replace the 2 gears and one shift fork. I scored a complete 2020 trans with 3 hours on it so I'm swapping the works. As for the FX 5th gear, buy the 2 gears and all new circlips and they slide right on. Instant close ratio YZ 1st-4th with a 15% FX 5th gear OD. Going to be awesome.

After all the crankshaft talk, mine at this hour level is still perfect and totally in spec. I bought a new one anyways because they are cheap but I would have no issues running the old one.

The cylinder has had one light hone at 80 hours and a new piston. It still measures good, another light hone and new piston, good to go doesn't even need a replate. Stock rocks. My cylinder guy says he can tell I've been doing enough oil changes by the lack of wear.

The head looks great for the hours. I dropped it off at my head guy for a port job to match the Hot Cams I'm going to run, new seals, check the guides. Good to go. Funny thing, head guy had the exact same comment about the oil changes as the cylinder guy.

The clutch is pooched. The frictions measure 3.01 mm which is 50% but it has been super hot at some point because the steels are a nice shade of blue, like as in really blue.

The starter clutch has gotten hot at some point as well, it seems to still be fine but it's getting a new one.

One of my trans bearings is rougher than I would like but overall the bearings in the bottom end seem great. It's getting all new bearings anyways, why would you not at this point.

Basically if your trans all seems fine, do top ends every 100 hours or less, run good oil and change oil in the 5-7 hour range and just ride the pi$$ out of it until the trans fails, I wouldn't crack the bottom end until it shows some reason to do it.

M5

 

[wwillf01]

Are you going to treat the trans at all before putting it back?


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[M5-]

I thought about cryo (sp?) but if I can get those kind of hours out of it as is then I can live with the shifting characteristics. I know treating it would make it shift better and probably last longer but I had to draw the line somewhere. This bike will become the "B" ride next season and I will get something new. I do like the look of the Beta.

M5

 

[Brayjay]

Unless I missed it what did you run for oil?

 

[M5-]

I've been running T6 for years. It clearly woks fine.

M5

 

[M5-]

I just thought I'd provide an update on the rebuild. I got 2 days on it last week before I got sick as hell so I had to take some time off. The main differences over stock are the cams, head porting, Airforce velocity stack and the transmission mod.

First off, if you are going into your YZ at any point in the future add the FX 5th gear. The motor just settles in and cruises on the trail, no more screaming in 5th. I decided to let-er-rip and my sled buddy clocked me at over 70 MPH, 50 MPH is effortless. I'm running a 14 tooth on my Yeti kit so it was pretty quick to begin with, now its crazy fast, scary actually.

I added Hot Cams stage 2 cams and I had LRX Performance port the head for me and I added the Velocity stack, all mods designed to flow more air, all on the stock bore. The thing that surprised me about this combo is how much bottom end it added. The thing just pulls right through the rpm range. I was expecting all top end but this is a huge bonus/improvement. I haven't checked the valve overlap specs on the Hot Cams as compared to the stockers but I'm sure some of it is that. The Velocity stack dyno data advertises more bottom end torque so some of it may be from there. I didn't change my tune from last season but I have now. I suspect my old tune had way to much top end timing so I've written a new one, we shall see, I'm hoping for more yet. Really a dyno is the only way to truly set it up but I don't have one. It would be nice to have an A/F setup with data logging but for now its the ass dyno.

M5

 

[Answ3r]

I've been running T6 for years. It clearly woks fine.

M5

I've ran T6 in tons of machines for years, but on a KTM since it ask for 10w50, I'm concerned about running a 5w40 that is known to shear to a heavy 30 in a gearbox. Kinda wonder how the engine would like a thinner oil when hot.
Yam calls for 5w30 in winter and 10w40 in summer IIRC ?

 

[M5-]

I think a lot of it comes down to frequency. I change my oil depending on the days of riding and it usually happens between 5 and 7 hours of run time. Any good quality synthetic oil should be able to last that long. If my engine called for heavier oil I would probably run that grade just because I can be a little anal about that stuff. I kind of look at the Yamaha as the Chev LS of bike engines. Does it make the most power, no but its reliable and easy to live with and isn't all that fussy if you look after it. The KTM is more the BMW/Mercedes style engine, a little closer to the edge hence the added power.

M5

 

[Answ3r]

I think a lot of it comes down to frequency. I change my oil depending on the days of riding and it usually happens between 5 and 7 hours of run time. Any good quality synthetic oil should be able to last that long. If my engine called for heavier oil I would probably run that grade just because I can be a little anal about that stuff. I kind of look at the Yamaha as the Chev LS of bike engines. Does it make the most power, no but its reliable and easy to live with and isn't all that fussy if you look after it. The KTM is more the BMW/Mercedes style engine, a little closer to the edge hence the added power.

M5

100% with you on that.
It's just that "thin" winter oil are hard to come by in the 50 hot weight.

 

[GlennRMK]

I think a lot of it comes down to frequency. I change my oil depending on the days of riding and it usually happens between 5 and 7 hours of run time. Any good quality synthetic oil should be able to last that long. If my engine called for heavier oil I would probably run that grade just because I can be a little anal about that stuff. I kind of look at the Yamaha as the Chev LS of bike engines. Does it make the most power, no but its reliable and easy to live with and isn't all that fussy if you look after it. The KTM is more the BMW/Mercedes style engine, a little closer to the edge hence the added power.

M5

I disagree. Seems like the KTMs are tough from what I've seen.

It seems like the 2018+ Yamaha engines might be the worst from the last few years? Maybe they fixed them for 2020+ and/or 2023? Seems like I read about a lot of crankshaft failures.

My buddy has 2016 450 SX-F with over 400 hours on the original piston. He had FE501 with over 300. All hard snowbike use. His brother has a 2017 450 SX-F with about 300 hours on the original piston.

I don't care to go that long but its nice to know its possible. I'm at 160 hours on my 2019 Husky and plan on doing the piston around 200 hours.

 

[M5-]

I'll be honest with, I really don't know where this YZ crank failures story on 2018's YZs came from. The crank is the same part number all the ways back to 2010. The same guys who say the 2018 YZ has crank issues but the 2014-2017 was bulletproof haven't checked the part numbers. When dissecting Yamaha part numbers the 11400 or whatever it is for the crank I can't remember off the top of my head is the one that counts. The BR9 (2018 YZ) or the 1SL (2010YZ) indicate the series that's all the other numbers are all revisions. The latest on a new series will all be 00-00 until they make a change then it becomes 01-00 etc. Its the same crank. In short that is all internet BS as in my buddy heard that his buddy had a buddy who said his other buddy knew a guy who read the cranks were bad. ALL BS, FULL STOP.

I had to split the cases so I just threw in a new crank and rod while I was in there. Now I don't need to think about the crank until at least 350 hours if I were to actually keep the bike that long. You can buy a complete YZ crank with rod brand new from Yamaha for the same price as a KTM rod alone plus then you still have to rebuild the crank on the KTM, I know I've done it twice on my KTM. Putting in a new crank when you have the cases split on a Yamaha IMO is a no brainer even if the old one measures perfect which mine did. 170 hours is 170 hours no matter how the crank measures.

As for pistons I have no doubt the YZ would go 200 hours on a single piston but I'd be surprised if it didn't oval the bore. Will it fail at 200, no I doubt it, will it cost more to rebuild, probably if you need to Nic the cylinder and hone it back to round. Same for KTM, Honda, Suzuki, whatever brand there's a reason the manufactures have piston replacement interval recommendations. For the price of it a new piston, timing chain, hone job every <100 hours is my schedule. I have my 2 bikes on alternating rebuilds in the off season so that way I always have a newish one and only need to freshen 1 per year.

I did not mean to imply that KTMs are fragile because they aren't but they do tend to run tighter tolerances which IMO simply means take better care of it. Each to their own. I'll just ask this question, would you buy a used snow bike with 160 hours on it and no rebuild? I wouldn't because going through my head is "Time Bomb" maybe that's just me, again each to their own.

On a side note, I have friends who are terrible at maintenance and don't maintain their sh!t. The perfect bike for them is the 501 or the 500 KTM. Those are the reigning champs for durability without replacing anything. I think you could fill the crankcase with salad oil and they wouldn't fail, I hate how they ride but they are tough I'll give them that.

Well on a good note at least this hasn't turned into another oil thread, lol. yet

M5