I have a 2021 Yamaha YZ450F I got the bike with damaged to the cylinder, head and valve cover along with one of the cams was broke so after I got a new cylinder, head, a new valve, cover, and a new cam and put everything together. The bike start and I wrote it up and down the street fine but as soon as I started the exhaust coming off of the motor so I guess you’ll call it. The header starts getting hot really quick like within the matter of 2 to 5 minutes the rest of the motor seems to be fine and normal temperature. It was getting hotter before but I replaced the valve adjusting pad to be in spec. and went down in size and now it just doesn’t get hot as fast as he would before but he still does within the matter of 2 to 5 minutes before it was like within a minute so now that it’s starting to get hot just not as fast but within that short timeframe, is that normal or is there something else I should look at? I also replaced the ECU because the bike did not have one when I got it so I don’t know if the mapping can be off or something else but the bike seems to be fine except for that exhaust getting hot , I can use any advice or any help would be gladly appreciated
All 4-stroke MX bike exhaust headers get stupid hot very quickly. If you let the bike sit and idle for 2-5 minutes you'll be lucky it doesn't start pushing coolant out the radiator overflow, as it does not have a fan and needs to be moving.
I get that I’m aware but my 2014 crf 450r dose not get hot close to as fast as my yz. But it’s not the more the is hot it’s just the exhaust header
IF you're uncertain, would be good to check that your waterpump is working, that your cam caps aren't overtightened and that your cam chain adjuster is giving you good tension. Also check engine oil pressure.
As FGR says, bike is not meant to sit idle and will heat up QUICK!
Yeah.. one way to know for sure if it is an "abnormal" amount of heat is get an infrared temp gun and compare header temp to a known good YZ450.
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Ok cam caps are to spec 7.4 ft lb, cam chain has good tension I have not checked water pump and oil pressure cud it be that exhaust cam I couldn’t get both cams to line up the exhaust cam is like a tooth below the mark I can not get it to be in the right position once I let the tensioner tighten up I loss where it should be
Any other parts that you replaced that you did not post? Some very important parts are missing.
4 stroke MXers have had header glowing since the 1st YZ400F
If the exhaust cam is too advanced, then that's very likely why you're getting hotter at the exhaust. You need to go back and figure out why it's not lining up. Maybe a new cam chain.
Replaced cam chain now it lines up better but still getting hot
It takes like maybe 10-15 seconds for the header to get WAY too hot to touch. Is the pipe getting glowing red? Also letting the bike idle for 5 minutes is a overkill. I let my bike idle 2 or so minutes then slowly cruise to the track entrance. First lap is a sight lap so I am just putting around with no real load on the bike. 2nd lap bike is safely warmed up.
Tuning will effect pipe temp more than any other factor.
Thank everyone for the help. So here is my update so I was starting to think maybe that’s just how these Yamahas are home so before I finally took it out on a ride, I I switched out the plug for one that is more suitable for hot weather since it’s been really hot lately so after I change out the plug, I then started up the bike. I noticed it wasn’t seeming to get that hot so I decided you know where I’m gonna take it out for a ride and see how it gets when it’s actually on a ride not just up and down the street and then I decided just in case it does get hot maybe I should do this with cooler weather so I waited till night, or at least until the sun went down and I wasn’t so hot and I took it out and it didn’t seem to be getting hot just like a normal temperature. I would assume at the end of my ride my leg closest to the exhaust seem to not even be as hot as it would’ve been if I was riding my Honda CRF 450 so I want to say the problem is no longer an issue in the bike in a long as it’s hot, I don’t know if it was a spark, plug or what or maybe it for me actually getting it out there instead of just riding it up and down the street going through first and second being that I live in a small cul-de-sac
Swapping plug heat ranges is nothing more than a band-aid for improper tuning. More fuel would be the way to go instead. Truly you have not indicated that was necessary either, only that you pipe is "Hotter Than A Honda" and may be totaly acceptable. You are barkiing up the wrong tree. Sounds like you do most of your riding in shorts.
4-stroke exhausts get really hot. It's a function of the material and the fact that the pipe doesn't expand, like on a 2-stroke. (Part of the 2-stroke tuning magic is via the expansion of the exhaust gases, which makes them cooler.)
It would not surprise me to find out that a 2-stroke exhaust pipe is about 200 degrees and a 4-stroke is at least double that.
I joke to all my friends that the designers came up with one more thing to make me hate 4-strokes: "In addition to making it heavier, louder and stall more easily, let's make it BURN THE SHIT OUT OF YOUR LEG! YEAH!"
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