$3500 top end overhaul

[monaro308]

It's the avergae punter cost's we are talking here,not competitors race bike as we all know they are maintained better ie silly money thrown at it including the ever important sticker kit.
I reckon if my WR450 threw a leg out of bed and destroyed top and bottom end....i pretty sure it "may" end up as a parts bike.
This is a VMX site and yes all you will hear is stories about arthur and martha's bike......but if you jump on thumpertalk.com....and read what is going on everyday......there are a few asking the question...."i am thinking about buying a 2 stroke again,i had a ride and had a ball,it was very light and so on...
Anyway.....2 Vs 4 strokes can only be answered when you have to pay for that next major rebuild.

[jack82]

Unfortunately there's little choice for someone looking for a weekend trail bike with decent suspension, electric start and a solid low maintenance engine except for the DRZ/KLX clone bikes of a couple of years ago or perhaps a Euro 2 stroke. What do you guys suggest?

XR650R........Yeah I know it's not lecy start but they are a great,bulletproof,low maintanence allrounder.I use mine for everything from single track to multiple day rides.......mainly around Dargo and the VIC high country.Very versatile bike.......I"ll never sell it.....

[Marc.com]

XR650R and 400s were awesome unbreakable bits of gear that really got the job done. DRZ400 was also same era. I guess the makers can't win, when they build soft bikes everyone is hotting them up, when they build hot ones everyone is bitching. 

The CRF450X is probably a good thing as Honda changed the valves and softened the cam timing, but finally the motors are pretty light and built light compared to the more solid lumps that were in the XR650/400/

[tony27]

Thats the reason for the difference between a xr & crf, the xr has a lot more metal to move around which limits power so the state of tune is lower. Never seen the piston in a xr or drz but i'm guessing there will be more skirt on them

[mx250]

[Nathan S]

Thats the reason for the difference between a xr & crf, the xr has a lot more metal to move around which limits power so the state of tune is lower. Never seen the piston in a xr or drz but i'm guessing there will be more skirt on them

Surprisingly, the (virtually non-existant) length of the skirts are rarely the source of the dramas with these bikes - if anything, the pistons are one of the few items that shows signs of being near the end of its life, before going boom.

The real killer is the valves - this is caused by very aggressive cam profiles, and thin valve stems. As a far more knowledgable mate said "These things close their valves with more force than a Holden red motor would with the worst possible valve bounce you could imagine" - he was exaggerating (I think!), but the point is still clear....

Add in 'Australia's super fine dust' and often low quality titanium, and its a wonder they make it out of the dealer's driveway.

The other semi-regular killer seems to be blow big ends. This seems to be a mix of poor maintainence and the fact that the rods are quite highly stressed. Whereas a 2-stroke rod or an old-style 4-stroke rod can be basically expected to last forever (at least until a worn big end bearing damages it), many of the newer stlye 4-stroke rods seem to have a finite fatigue life - so they can break/blow even if the big end bearing is healthy.
(I am happy to defer to greater knowledge/experience on this one).

[Lozza]

The fine particles from the clutch plates do big ends no favours and cause premature wear.KTM use different oil for transmission and engine.The valves are coated in titanium not full titanium as that requires a berilliyum copper valve guide and seat (@$200 each plus fitting). The factories found coatings that would not need the seats/guides, that is why you never lap valves in today.The use of valve saver is recommended a lot these days.
I don't think the roller bearing v's plain bearing makes that much difference, Honda MotoGP engines were quoted as having a 300km service life before being sent back to Japan for a rebuild.You would expect a MotoGP full factory engine to be designed and built  'right' from the outset.Your rebuild on a RC211V would be a fraction more than $3.5k
A 500cc 2T GP bike would use 3 sets of pistons/gaskets/o rings in a weekend, replaced at the end of each day..............at the track by the teams mechanics.

[ChrisACT]

MotoGP engines each have to last 3 rounds this year.  I wonder if they will.

[crash n bern]

I think the problem with the modern 4T is that their trying to 2T them to attract 2t riders.   They're using 2t bottom ends, short stroking them and making them rev to 13,000 rpm.  What do you think will happen? 

Unfortunately it makes the bikes suck for 4t riders.  I had a WR250F and I had to ride it on redline to get any go out of it.  That's not why I ride 4T's.  I want low down lugging that a long stroke 4T is all about.  They don't make that anymore.

I bought a 2000 KTM520 back in 2001.  It's done a lot of K's and has had one top end rebuild that cost $1,300.  All my mates ride KTM's and all have had good runs out of them with occasional top end freshen ups all running at around $1,000 - $1,300. 

When the  KTM 4T EXC'S where first released in 2000 It was stressed by KTM and the magazines that these where high maintanence  race bikes and not to be bought by joe average trailrider.

If you want a performing reliable 4T trailbike with good suspension consider a KTM LC4

Firko, the bike for you would be the 96+ ATK with the offset crossover frame. Low seat height, good handling, as light as a modern 4T.  Just feel heavier to ride because of the flywheel inertia.  You would just have to upgrade the suspension, but a set of later model KTM forks will slip right in.

http://www.bikesales.com.au/all-bikes/private/details.aspx?R=3148852&__sid=126A4AB6195E&__Qpb=true&Cr=0&__Ns=p_RankSort_Int32|1||p_Make_String|0||p_Model_String|0||p_YearMade_Int32|1||p_PriceSort_Decimal|1&keywords=&__N=1432%20604%201430%201429%201428%204294964316&seot=1&__Nne=15&trecs=1&silo=1400

And Frosty, XR600's where notorious for eating choke butterflys. Taking the choke out was part of the pre ride setup back in the day.  They're getting cheap now and would be worth snapping up.

[firko]

Firko, the bike for you would be the 96+ ATK with the offset crossover frame. Low seat height, good handling, as light as a modern 4T.  Just feel heavier to ride because of the flywheel inertia.  You would just have to upgrade the suspension, but a set of later model KTM forks will slip right in.

Great minds think alike........I've owned both 406 2 stroke and 506 4 stroke ATKs over the last few years but have sold 'em both before I could get them to Australia. I'm a bit concerned about getting an import registered without ADR certification. I've had a few different opinions but nobody''s given me a definitive answer. I guess I'd get the official answer with a phonecall to the RTA but it hasn't got that far yet.

I've ridden a few ATKs and they're brilliant but I have to question the "low seat height". I love the lugging power of the big Rotax stroker..what a motor! Ditto the forks. The standard Paolis are a bit of a pig to set up but once done they're pretty good. I just sold a pair to a bloke in Bendigo who's putting them in a BSA B50 of all things. Methinks they'll be back on the market again soon. .........you've got me thinking again. If I can get one registered, I'd even consider the later ATK250 2 stroke, with electric start. They're as cheap as chips in the USA.

[frostype400]

Funny you should mention the xr600 eating choke butterflys my mates did it a while ago but still wasnt a big $ job to have it fixed.

[crash n bern]

Firko, Bert Flood bought in quite a few 406's, 605's and 250LQ's from '94 on.  The 406's weren't complied but the 605's and 250's where.  Some of the 94 and '95's where plated as 96.   'The 605's came in cross country which had no compliance or dual sport which had compliance.  Talk to Dave at BF imports he knows a lot about it.  May even be able to still comply them.

The '95 models where very tall.  You had to be 6' plus to feel happy on it.  One of the negative issues that came up about it.  At 6'2" It was tall for me.
 But the 96 and on (like the one in the link) had a very low seat height to address this, as they had completely redesigned the frame.  Frank White had sold the factory and the new owners tried to boost sales with a new design. ( Frank White has since bought it back.) 
 I'm not sure what year the Paolis came on board might of been 98 or so.  Most of the ones Bert Flood sold had the WP forks and rear shock.  But the WP forks where the 40mm ones that I believe don't have any low speed compression dampening.  They're OK, but a set of 2000-2004 WP off a KTM would fit straight in.  The other issue is the rear shock is pre PDS and as it's a non linkage setup there could be some  improvement  made there.

Dirtbike magazine tested the 95 ATK in their 600 shootout.  They said the rear end skipped around like a lizard on a hot grill and for the money (The ATK was the dearest bike.) They hadn't gelled all the components into a complete package.  I bought the bike anyway and found it to be true. The 96 handled a lot better.  Oh and the XR600 won the shootout as best bang for your buck.   The ATK sold here for $300 more and was way sexier than the XR so I went that way.  In hindsight I should of bought the KTM620.

So Firko if you want a registered one, there are quite a few in the country that come up for sale fairly regular.

Frostype I mentioned the choke issue because I read your post.

If you need any ATK info feel free to PM me to save hi jacking this into an ATK thread.

[CamP]

I've had three new CRF450's since 2003, put over 500 total hours of motocross on them, and never had a valve cover off any of them. I would have gone through ten 2T top ends in the same amount of time.

[kristan]

I rebuilt my crf. new piston, inlet valves , springs and retainers, main bearings, all seals, brand new stroker crank, gaskets, hour meter for just a little over a $1100. all parts from US ebay.
cant complain!

[GMC]

Funny thing is I was talking to some old guys last year, yes much older than me
They claimed that they lost interest and became disillusioned with MX when those unreliable and expensive to maintain, high maintenance 2 strokes took over the game