CR450F Top End Update

[EricGorr]

CR450 Top End Maintenance Update

The Honda CR450 that I’ve been maintaining for District 16 expert Tyler Smulders, has required a bit more top end care because of usage and typical abuse that can’t be avoided in racing. If you read this forum you may remember an article that I wrote in the spring regarding servicing the piston and rings. This is what’s happened since then.
Tyler accidentally over-revved the engine by downshifting one too many gears in an effort to let the engine absorb the G-force of a hard landing from over jumping a plateau jump.

The stock rev limiter only works on acceleration, there is no protection when downshifting. One of the intake valves floated beyond the limits of the valve spring and clipped the piston crown and shattered the intake guide. The fragments bounced around in the engine and damaged the piston and head. I was surprised that the cylinder didn’t get scared. I replaced the head, piston, and one intake valve, spring, collets keepers, and gaskets. The parts were very cheap. Service Honda sold me the head for about $215; compare that to an YZF, which is a staggering $750 for a new, bare head.

One minor problem that I had when assembling the new head, the shims that I needed were on back-order. In fact I ordered a complete set of shims for the CRF and I finally received all the shims at the end of June. Instead of waiting for the Honda shims I went to a local multi-franchise motorcycle dealer and matched up a shim with the same diameter from another common street bike. I’ve shimmed the valves three times over the course of about 200 riding hours. The valves were tight each time. That’s a bit often compared to an YZF, but considering the difference in cost of the parts, the Honda head is designed to be disposable like a piston. For the low price of a head it doesn’t even make sense to port it or refinish the seats and replace the guides like the old XRs. In my opinion, that’s a good idea. Most of the YZF heads that I see for service in my shop have never had the valve clearance shimmed and they’re real clapped-out. The Japanese manufacturers have been struggling with the American dirt biking public over maintenance of high performance 4-stroke singles. Hey guys, that pitch that the magazines give you about 4-strokes being no-maintenance is a myth. These engines aren’t the 1975 Country Squire station wagon, they’re 1/10 of a Formula 1 racecar engine! They need the oil changed frequently and the valves adjusted periodically. Consider this, the average cost of an engine rebuild in my shop for an YZF is $1,000 on a 2-3 year old bike. For the west coast hop-up shop currency exchange rate, multiply that times 1.9 You guys can buy a lot of oil and filters for a grand.

Big Bore Alternatives
Its been about six months since the cover of MXA featured a test on a Wiseco kitted CRF with a 500cc displacement. Here is the status of that project. Wiseco in Ohio offers an exchange program whereby you send them a clean core cylinder and they send you a modified cylinder. This is how the cylinder is modified. The cylinder is bored and fitted with a forged aluminum liner then TIG welded at the top. The stock cylinder wall isn’t thick enough to support the 101mm piston and that’s the main reason why a liner is required. The cylinder bore is plated with nickel composite by Millennium Technologies in Plymouth Wisconsin. A Wiseco piston kit and Cometic gasket kit is supplied in the kit. The part number for the kit is CK137 and retails for $995 without a core exchange. Wiseco is in the process of casting a new cylinder with larger water jackets in an effort to reduce the price down to the $750 range. I have one of the lined cylinders on order and will report to this forum my experiences with installing and riding the bike with this kit in the near future.

 

[OMEGA]

That really gets me to thinking, as well as every other privateer trying to decide between the 2003 CRF and YZ.
Cost effectiveness weighs big in that decision.

 

[marcusgunby]

Eric thanks for pointing out the maitenance requirements on the new 4 strokes-i keep banging on how they actually require alot of care.2 strokes now days IMO are very robust-my 125 gets airfilter clean every ride, gearbox oil every other ide and piston ring at 6 races, piston is 12 races-this work doesnt require many hours at all.If anyone is buying a 4 stroke for less downtime IMO they are misinformed.

 

[bigred455]

My opinion only,4strokes have more moving part's, valves, cam chain,etc.More moving part's, better of a chance something go's out.Eric I understand your article is not to discourage anyone from buying a 4 stroke.I thought about it hard after I rode a crf and yzf they were both sweet.I just think their is too much involved with the motor compared to a 2 stroke. FINAL DESCISION 03 KX 250 COMING. GOOD ARTICLE.

 

[MxKid512]

Eric,
That price difference is very interesting. I had no idea. 500 dollars is a lot of money to save when you're rebuilding an engine. Thanks for the info.

 

[crkid]

I love these new threads you've been starting like this one and the one about stroking engines. Expanding my knowledge and answering questions I hadn't thought to ask. Thanks. :cool:

 

[kev_rm]

Eric, I think all these things coupled with the fact that 2-stroke top end maintenance is *so* ridiculously easy... I think it's 6 of one, half dozen of the other.

 

[EricGorr]

Your comments are all interesting. Overall I think that the magazines have started this "4-strokes are easier, better, and less maintenance" conspiracy in order to appease the Japanese manufacturers and lure in more ad bucks.

Maybe some resaponsible magazine editors would be willing to invest editorial pages towards raising people up the learning curve by writing articles like these and ones geared towards preventing catastrophic melt-downs. I find it disturbing that so many people part-out their 2-3 year old YZF because the engine blew up and they can't afford to fix it. Its partly due to the high parts prices that Yamaha sets on this model, and the fact that the magazines focus on the favored few aftermarket companies as experts in hopping-up and repairing these engines for outrageous prices. NAAHH I guess that will never happen!

Instead we'll keep writing and posting threads to address this topic on DRN

 

[Hondaxrguy]

Originally posted by EricGorr
Instead we'll keep writing and posting threads to address this topic on DRN

I look forward to reading them!

It's nice to see a useful write up about bike maintenance. The cost of replacement parts is rarely considered in the purchase of a bike IMHO. :|

Jeremy

 

[Matt_H]

So how often should a person checking up on the valves?. I believe its not only the mags that say there're maintaince free, my dad and I went to look at a yz250f and the dealer said that they've never had to touch neither the 426 or the 250 since they have come out. Know that I've read what you have to say makes me kinda wonder about the dealer.

 

[BRush]

Originally posted by EricGorr
...I find it disturbing that so many people part-out their 2-3 year old YZF because the engine blew up and they can't afford to fix it. Its partly due to the high parts prices that Yamaha sets on this model...

I'd sure like to see rebuild costs given more visibility when the magazines do their tests. That would at least put pressure on companies like Yamaha to moderate their parts markup.

 

[EnsignB]

I think I remember Dirt Bike magazine in the '80s showing prices for the parts to rebuild at least the top end on the 2 stroke motocross bikes. Haven't picked up one of their magazines lately, but it would be nice to include this info on all bikes.
-----
Brandon

 

[hapanese]

I was considering buying a YZ 450f until now. The CRF is still a possibility. Thank you Mr. Gorr.

 

[2smoke]

Two Smoke says: Hehehehehehehehehe!!!!!!! Eric Ive been telling these 4 bangers for a couple of years now that to get that 4 banger going so hard they cut up a formula one engine........they all still think a bit of a oil change, the filter and voila....the original no maintenance bike. Too many grew up on XR's!!!!!

 

[patpipes]

I don't know of anyone who has had a Yamaha head wear out yet, I check my valves and they are fine plus it starts everytime. If a former 4 stroke world champion can ride one for 2 years without problems it should last me 6 years. Might want to check around with the thumper national riders to see what bike is the most reliable!

 

[P. Pinestraw]

I know a guy who races a CRF450 in THREE off-road race series and, including practice, has put over 160 HARD hrs. on the bike & hasn't even adjusted the valves. He plans on adjusting the valves in late July & replacing the piston and rings about X-Mas time or thereabouts. By the way, he is a "B" or intermediate rider. Very fast & highly skilled.

 

[marcusgunby]

pat i think the problem with the head comes from poor quality or not often enough oil changes-this means although the engine isnt at fault the replacement costs are significant.

 

[SFO]

Honda has done an excellent job at making their parts affordable in an effort I believe to get people to adhere to their maintenance schedules.
I think the cassette head is a great idea. It also stops the head rebuilders in their tracks when a new head is so cheap.
The honda valves are also designed to be replaced, not refaced, so you must replace them too.
I believe with the current crop of ti valve heads the engineers have pushed the envelope as far as seat pressure and valve acceleration.
The result is that when these springs get tired they no longer control the valve properly and the errosion of the face and the seat is accelerated.
I would/and do, replace my valve springs with every rebuild. The yamaha springs are cheap, less than 10$ each.
There are many spurious viewpoints regarding blue vs. red and 2vs.4 stroke and I think perhaps the real issue Eric was commenting on was how surprised he was that the honda parts were affordable compared to yamaha parts in regards to a bare head.
It seems that two the most frequent topics I see on the 4smoke boards are
I don't need to folow the service schedule because my motor is in spec, and my motor blew up honda/yamahas are junk.
The measured specifications are not the end all for the service intervals.
Service life=fatigue cycles on things that cause catastrophies.
Rods and valve springs are two items that replacment (I believe) is the only way to insure non-failure.
Heck a complete cr-f crank is only 200$ right?
It is a real can of worms to create your own service schedules.

 

[dell30rb]

okay, so what regular maintenance should be done to keep these things from grenading? So far I've heard religious oil + filter changes, and valve adjustment?

Please enlighten me.

 

[Thump]

Eric,
The YZF is a great deal more expensive but does the super light piston of the Honda require any more frequent top end rebuilds or maintenance than the YZF?

 

[SFO]

Originally posted by dell30rb
okay, so what regular maintenance should be done to keep these things from grenading? So far I've heard religious oil + filter changes, and valve adjustment?

Please enlighten me.

I am unsure I could enlighten you but am reminded of an experience I had working for a firm that built stern drive units for offshore racing boats.
After every race there was 100% disassembly and inspection of the stern drive units which resulted in zero failures.
When I questioned the intensity of service intervals my employer said that when they built racing engines every moving part was replaced after every race and proceded to show me cases of carrillo rods that ran one race.
It seems to me like finding the middle ground between replacing broken parts and replacing what appear to be good parts is different for every rider.
If the goal is 100% reliability I would start with suggested service intervals.
I am pretty sure Hendricks doesn't run the same motor two weekend in a row.
The "middle ground" of end user vs. factory servicing is a very difficult to define.
Almost like recommending a motor oil :eek:

 

[motometal]

for those of you talking about situations where four stokes went years without maintenance, this doesn't surprise me at all! Many modern two strokes will run for years and years without a mechanical failure, and when they do get rebuilt, it will still be cheaper than a rebuilding a tired four stroke.

I'm not saying one is better than the other, but I'm tired of the common opinion that two strokes just self destruct and fly apart after 20 hours (or whatever the book says).

If you want to see some fine examples of old faithful two strokes, just go to your local sand pit or open riding area on a Sunday...there are two strokes from the 80s that have never been rebuild that still run great!

 

[Anssi]

Originally posted by motometal
If you want to see some fine examples of old faithful two strokes, just go to your local sand pit or open riding area on a Sunday...there are two strokes from the 80s that have never been rebuild that still run great!

Exaggaration seems to be the order of the day. No two-stroke that has been run, say, 1 hour/week since the 80s without rebuilds will run great. It might run, but no-one in their right mind would call it great.

 

[Ol'89r]

Eric.

Do you think it would be a good idea to machine a set of silicon bronze guides for the CRF head? We ran those on our old flat track engines. They came stock with cast guides and it only took one missed shift to destroy a head. With the silicon bronze guide, you could bend a valve and nick the piston but they didn't shatter.

On our own racing engines we would pull them down every 2 races to do a topend and every 4 to 6 races on the bottom end. Of course, we didn't have the money to do a complete rebuild after every race like the factory teams.

We re-used many of the old parts, but had them tested and treated each time using Magnaflux and Zyglo testing proceedures and then had them shot peaned.

Today, there are better testing and treatment proceedures available. I would think this would be a better way to go instead of just replacing everything.

But then, what the hell do I know???? :confused:

 

[motometal]

anssi, you will note that I didn't specify that the bike had been used weekly.

basically I am agreeing with Eric that the magazines, and others, have really exaggerated the low maintenance aspect of the modern four stroke race bike.

At the same time, many are stuck on the mindset (which may have been accurate 25 years ago when two strokes were air cooled) that two strokes require frequent top end maintenance. This simply isn't true.

I will say that logic and physics tell us that, all other things being equal, there will be parts (such as the piston) in a two stroke engine that won't last as long as the same parts in a four stroke engine. Why? well, for starters, more force (or equal force) over a smaller area equals more wear. And since two strokes require significantly smaller pistons to make equal power, it's only logical that there will be greater wear, all else being equal.

If the top end lasts twice as long, but costs three to four times as much to rebuild, I would hate to list "low maintenance" or "low maintenance cost" as a benefit of a four stroke. "infrequent maintenance", well maybe...