Engine rebuilds ?


18 replies to this topic
  • genjuroq

Posted September 30, 2008 - 01:45 PM

#1

So, from what I've tried to read is that the modern 4 stroke MX bikes require rebuilds more often than say a 2-stroke 250. Or if not more often, at least as often but at a higher cost. I'm looking at getting an '06 450 to use as a trail / play bike. Am I really going to be in for rebuilding my engine often? How often should I plan for based on the fact I won't be racing it?

Thanks,
Gen

  • Family Man

Posted September 30, 2008 - 01:56 PM

#2

Depends on how fast/hard you ride.

  • genjuroq

Posted September 30, 2008 - 02:16 PM

#3

Well, hm, I dunno. I want to ride every couple weekend. 4-6 hours each time. Wooded trails and sand dunes. Nowhere near race pace.

  • grayracer513

Posted September 30, 2008 - 02:26 PM

#4

Well, let's see, on my son's YZ250F, I did the rings once, and the valves twice in 2 1/2 years (bought used in '03, no previous work). The second valve job I attribute to improper seat work on the first one.

Then I had an '03 YZ450 that I bought used in '04 that never had anything done to it at all (never even needed a valve adjust), other than one timing chain for maintenance up until the time I sold it in January of '08.

I bought my son's '06 YZ450 new in June of '06, put a timing chain in it last spring, and while he's at boot camp, I'm going to replace the head gasket on suspicion of causing coolant loss, and throw in a set of rings, 'cause he really does ride it pretty hard. That will end up costing me $70.

My own '06 had two rides on it when I got it used in September of '07. It's not due for anything yet.

So, yeah, they are expensive to overhaul, when that actually becomes necessary, or when something goes bang, but don't worry about it too much.

  • llamaface

Posted September 30, 2008 - 02:56 PM

#5

Well, let's see, on my son's YZ250F, I did the rings once, and the valves twice in 2 1/2 years (bought used in '03, no previous work). The second valve job I attribute to improper seat work on the first one.

Then I had an '03 YZ450 that I bought used in '04 that never had anything done to it at all (never even needed a valve adjust), other than one timing chain for maintenance up until the time I sold it in January of '08.

I bought my son's '06 YZ450 new in June of '06, put a timing chain in it last spring, and while he's at boot camp, I'm going to replace the head gasket on suspicion of causing coolant loss, and throw in a set of rings, 'cause he really does ride it pretty hard. That will end up costing me $70.

My own '06 had two rides on it when I got it used in September of '07. It's not due for anything yet.

So, yeah, they are expensive to overhaul, when that actually becomes necessary, or when something goes bang, but don't worry about it too much.


your post would be more helpful if you listed the hours on those bikes.

for the original poster, it seems like many folks who are trailriding (or even doing some racing) are getting 200+ trouble-free hours out of yz450f's. My research leads me to believe that the yz is by far the most trouble-free modern 4-stroke engine, followed closely by the ktm RFS engine (used up through 07, and still used by Beta).

200 hrs is at the far end of what most would consider reasonable for a 2-stroke engine as well. The 2stroke has the advantage that even a spaz like myself can put a new piston in. I'm probably not qualified to replace valves on a 4stroke, but if money is tight, you could probably do most of the grunt work yourself and just bring the head to a qualified mechanic.

Anyhoo, I am looking at getting a yz450, and based on what i've read and heard, and my experience with other bikes, I think I can expect 200-300 hrs of service (a little less than a year) before having to spend any dough. (i'm pretty easy on motors for whatever reason).

  • grayracer513

Posted September 30, 2008 - 03:17 PM

#6

your post would be more helpful if you listed the hours on those bikes.

Are you running an hour meter?

  • llamaface

Posted October 01, 2008 - 06:31 AM

#7

Are you running an hour meter?


Yeah, all my bikes have an odometer that also lists rolling hours. Probably only 99% accurate since it counts the downhills where i'm coasting with the engine off. I personally have hard time keeping track of when to change tranny oil, check valves, etc... on 3 dirtbikes and 2 streetbikes without some way to keep track. If you don't use one, then never mind, but maybe try to give more info like how often you ride and for how long and how hard ?? Perhaps the long-time members of this forum already know that info about you, but we newbies (the ones who could most use that info) don't know.

When people say "i've had the bike x years and done nothing to it" the interested researcher has no way of knowing if those people ride once every 2 months at the track for an hour or so, or practice twice a week and race every weekend year-round, or ride 10-12 hrs/week in the dez, or what. I think that kind of info is fairly important in assessing durability and reliability. I try to always mention my style of riding (smooth, low revs, easy on the engine) so that people know that the large number of problem-free hours my bikes see may not be applicable to someone who revs higher, or goes slow enough in technical stuff to overheat the bike, or whatever.

  • grayracer513

Posted October 01, 2008 - 07:07 AM

#8

Hours in and of themselves tell only a part of the story, anyway. 5 hours of rolling around casually in the woods are nothing like 2 hours of racing in the desert, which is probably not the equivalent of one hour of A or B level MX racing. So, it's not as totally informative as some might think.

My son and I average around 100 hours a year of hard recreational riding, desert racing, MX practice sessions, etc. The recreational riding includes playing in the dunes quite a bit, too, and that can be pretty demanding on the engine.

  • llamaface

Posted October 01, 2008 - 07:28 AM

#9

Hours in and of themselves tell only a part of the story, anyway. 5 hours of rolling around casually in the woods are nothing like 2 hours of racing in the desert, which is probably not the equivalent of one hour of A or B level MX racing.


100% true, that's why I like to know both hours/miles and type of riding in these discussions. Thanks for the additional info.

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  • Wiz636

Posted October 01, 2008 - 08:49 AM

#10

From my own personal experience two strokes have always cost me more in maintenance than my two YZ450's. I do quite a bit of offroad racing and fast trail riding when I'm not racing. Maybe it's because when I ride two stroke bikes I am always 'on the pipe', I don't know, but I end up having to do top ends about three times as much as on my YZ's. Yes, doing a top end on a thumper is more $$ but with proper maintenance it does not have to be done very often.

Add in the cost of premix (which can add $2.00 - $3.00 per gallon depending on what premix you use) then thumpers come out less expensive to operate as far as I am concerned.

  • genjuroq

Posted October 01, 2008 - 08:51 AM

#11

Excellent information guys. Thanks so much.

Gen

  • grayracer513

Posted October 01, 2008 - 08:59 AM

#12

Yes, doing a top end on a thumper is more $$ ...

I don't know if I totally agree with that. I have seldom done a top end on a two stroke other than a CR500 that did not need a piston. OTOH, most of the YZF tops I've seen apart had pistons that looked virtually wear free, and I would and have put them back together with just the rings. As I said, rings and gaskets and a new pin only add up to $60 plus shipping, and while I haven't seen the inside of it yet, that's all I'm planning on doing to the 450.

However, the pistons, when needed, aren't cheap, and doing a valve job on one is a whole other proposition.

  • KJ790

Posted October 01, 2008 - 09:14 AM

#13

I have done the math, and also kept track of what was spent for my bikes. In the end they come out about the same for me. I used to rebuild my tow strokes every 30 hours. It would cost me $100 for a piston, rings, wristpin, gaskets, etc. I rebuild my four strokes every 50 hours (to be safe). It costs me $150 for the same parts (piston, rings, wristpin, gaskets, etc). It costs a little more, but I rebuild less often so it is a wash. To replace the valves on a Yamaha it will be about $350, but if you change the air filter and oil regularly they should last a long long time (I've never had to replace the valves in any of my yamaha's). I always ran 20:1 premix in my two strokes, so the oil cost is about equal for me between a two stroke and four stroke.

  • Wiz636

Posted October 01, 2008 - 10:16 AM

#14

I don't know if I totally agree with that. I have seldom done a top end on a two stroke other than a CR500 that did not need a piston. OTOH, most of the YZF tops I've seen apart had pistons that looked virtually wear free, and I would and have put them back together with just the rings. As I said, rings and gaskets and a new pin only add up to $60 plus shipping, and while I haven't seen the inside of it yet, that's all I'm planning on doing to the 450.

However, the pistons, when needed, aren't cheap, and doing a valve job on one is a whole other proposition.


In terms of replacing rings/gaskets I certainly agree. I was factoring in a few other things such as cam chain, valve seals, and shims (if necessary). Replacing valves definitely drives the cost way up but it seems that with our YZ's it is so infrequently necessary that I would still wager that over the life of the bike that the operating costs are completely in line with a smoker.

  • grayracer513

Posted October 01, 2008 - 11:15 AM

#15

In terms of replacing rings/gaskets I certainly agree. I was factoring in a few other things such as cam chain, valve seals, and shims (if necessary).

Point taken.

  • llamaface

Posted October 01, 2008 - 01:33 PM

#16

Add in the cost of premix (which can add $2.00 - $3.00 per gallon depending on what premix you use) then thumpers come out less expensive to operate as far as I am concerned.


I spend about the same on premix and tranny oil(per hour of riding) for my 2-stroke as I do on engine oil for my 4-stroke.

I don't think it's the top-end costs that kill ya so much as valve replacements. Also many people (like me) are a bit more intimidated about working on a 4stroke, and special tools and stuff to deal with valves and camchains.

Fortunately, yamaha is among the most durable in that respect, but honda owners can expect to spend alot on valves. I noticed that dirtrider's kawi 450 had a rod failure at 90 hrs, so they recommend inspecting and replacing that fairly early. lol, 90 hrs is less than 3 months ride time for me in the summer!!

At any rate, I'll find out later this year when i get a 450. I find that with my riding style, I can pretty routinely go 200 hrs on a modern 2-stroke without problems. My 300 had 14,000 hard offroad miles when I sold it (900-1000 hrs), and i did the top end 3 times in that span, and never had to look at the bottom end.

Otoh, I know a norcal trail maniac and isde vet that had over 30,000 hard offroad miles on his yz400. I do not know what he had to do for maintenance over that time frame, but he was one of those guys that takes a mig welder on vacation and does all his own work.

Hopefully, based on kj790's excellent experience and record-keeping, I can get a longass time of trailriding and racing out of my 450, and I can come on here to get my hand held for new rings and camchains and stuff. :lame:

  • grayracer513

Posted October 01, 2008 - 01:55 PM

#17

... and special tools and stuff to deal with valves and camchains..

Unless you get into replacing the valves, you're talking about a feeler gauge, a 1/4" torque wrench, and a flywheel puller.

:lame: Hardly exotic stuff. A good beam type 1/4" wrench can still be found for under $80.

  • llamaface

Posted October 01, 2008 - 02:13 PM

#18

Unless you get into replacing the valves, you're talking about a feeler gauge, a 1/4" torque wrench, and a flywheel puller.

:lame: Hardly exotic stuff. A good beam type 1/4" wrench can still be found for under $80.


yeah, i was thinking more of replacing the valves. And at least on some bikes, cam chains require a special tool to rivet them together.

  • Wiz636

Posted October 01, 2008 - 02:15 PM

#19

Unless you get into replacing the valves, you're talking about a feeler gauge, a 1/4" torque wrench, and a flywheel puller.

:bonk: Hardly exotic stuff. A good beam type 1/4" wrench can still be found for under $80.


I fabbed an adapter out of an old chainsaw sparkplug wrench that allows me to use the cheapo Craftsman automotive valve spring compressor on my YZ. :lame:





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