What do you think is the best motor ever fitted to a dirt bike?

[OverTheHill]

Sorry Firko, you got me going. Gosh [bullet proof DT1's] i must be on a different planet down here [nz], [Brutes we are] just about every DT1 we sold new that got raced had gearbox trouble with rounded off dogs & soft selector drum groove high points. Broke the 1968 coarse tooth third gear & put it out the bottom of my own one & did the same 30 years later with a 360 but running that same type first DT1 box. Liked that gearbox because the ratios right through to top were evenly space where the next [DT1F--on] had like an overdrive top, but i still managed to round off dogs on 3rd & 5th in particular on the later box. Anyway, the first pic up here looks exactly as mine came out of the box, color & all. One day i'll show you what it looks like now [be in the RAT bike forum i think]. Still goes just like it should. I used to run EP90 diff oil in the box to dry & cushion the shock of full song clutchless gearchanges [what a brute] Despite all that i still love em & am still surrounded by various variation of the original 44 years later. "My vote goes toooo mmmm the DT1. ps. few of us broke the square s/rm too, pissed of now i threw the original frame & arm out about 20 years ago. Fk it i took many trailer loads of all sorts of bike junk to the tip back then. Depressed again now. I'll give a plug for my T100 metisse back in "67--now 'that' was bulletproof. Jeez the RH main [which was a press in bush thingy] was so flogged out that it just can't have had 'any' useful oil pressure but didn't worry it a bit & never stopped. Cheers.

[Simo63]

Okay so I know these don't figure too highly on our current hit parade or "must have" bikes but you can't deny the Honda flat single four stroke motor as fitted to early Z50/70/90 and 110 bikes has probably introduced more people to dirt bikes (and bikes in general) than any other motor ever built.

As bullet proof a motor as ever built and able to withstand years and years of abuse yet still start up and take some more.  Well done Honda   

[OverTheHill]

yes, taking husky's, back in my metisse days. When Gunnar Lindstrom was down here, we were out practicing or marking out a local club event for the weekend as i recall & he said here, do a few laps on this. [semi works 360 or maybe just one out of the box but think he bought it with him after doing Xmas Hills] anyway ruined me for life that did & basically felt half the weight & twice as powerful as the metisse. I was right confused after that i was.

[OverTheHill]

talking honda 50's [pushrod model] hell we had one for a 'tow bike' to tow in bikes from around town that broke down. It got DEATH but once again--never gave up. Can't say quite the same for the Honda 55 pushrod farm bikes we sold [before ct90's]as the Brute kiwi farmer used to 'twist' the gearbox mainshaft [or layshaft] through it's length & couldn't change gears [wouldn't slide along]. Still vote for them though as just Great motors & not designed for 20 stone size 14 boots riders with no feel for poor little motor, Around town riders on honda 50's had a problem with condensation in the [never changed] oil & the selector drum, being high up used to go rusty to the point of not changing gear. Change the oil & put a T bar on the selector drum retaining bolt [above final drive sprocket], give it a few whizzes back & forth to free it up & all good for a year. [I vote Honda this time--being greedy]

[brebel]

85 CR500 Loads of grunt but still flexible enough to trail ride

All watercooled CR500 engines! best 2t of all time.

[oldfart]

Suzuki 250  TS -RL -TM  Donk  they don't come any tougher or reliable....

[GMC]

Pick any of the Rotax disc valved engines. Pull clean everywhere, lug happily and still have an MX hit up top. Well made too.
Surprised anyone has put up anything different!

Having ridden a few Rotax engined bikes of late I would have to agree.
The CanAm I borrowed for Tallarook had an impressive motor, pulled nice down low and still had good power up top, very smooth

[yamaico]

I totally agree about the Yamahas but what about the old XR75? Absolutely bullet-proof.

[NSR]

I reckon one of the best dirt bike motors would have to be the Rotax disc valve.  
From the early 70s though.  They were still holding there own in the late 80s.

I would say you could do a list of bikes as long as the Yamaha motor.  Was there anything they weren't used in?  

 
    

[Tim754]

Agree with the DT/RT yamahas, but..... in the 125 VMX stakes I would go straight for the Suzuki TM125. Maybe not the power of the Honda's or even the RM's but go out race all the season without piles and piles of repairs, tuning and general expensive time consuming crap.   (Sorry about TM400.......

[80-85 husky]

The KDX 250 83- 85would be my all time 2 stroke motor favourite, tractor like low down running through a flatish strong surge that was so easy to ride. Pity about the brakes...

But....but nothing beats the early air cooled 500 husky 4 strokes. They rewrote the book on stunning hp, huge flexibility and an exhaust note that made the xr and tt's sound like a step thru. Once you learnt to start them of course , they were fantastic. I got banned from a club event on one once because I was waiting for the club 4/ champ on his sponsored xr 600 to catch up so I had someone to race... it would have cost him the championship if I had beaten him?? I cant figure it out either but it put me off club racing that's for sure. the old boys club syndrome is pretty petty.

But that husky motor, what a stunner, smooth bottom end, quite responsive, not all inertia like the TT and XR's were but building to a 125 rush when the cams cut in..... Woo Hoo....

[Husky500evo]

When I first saw this thread, I straight away thought of the rotary disc Rotax motor. Used in Can Am, SWM, ATK and probably plenty of other brands that I can't think of at the moment (like Portal). The 250 in particular makes a broad range of power that would give most big bores a hurry up. But I also later thought about the '83 Husky 500/510 fourstroke. Most people seem to credit/blame the Yamaha '98 YZ400F for the start of the latest fourstroke revolution. But I think that the Husky 510 was the start of the modern competitive fourstroke. I may be drawing a long bow, but I think that even the latest KTM fourstrokes can trace their heritage back through Husaberg , Husky 610s and right back to the original Thomas Gustavsson designed Husqvarna air-cooled fourstroke. 

[Lozza]

I reckon one of the best dirt bike motors would have to be the Rotax disc valve.  
From the early 70s though.  They were still holding there own in the late 80s.    

Then went on to crush the opposition in road racing, the air cooled Can Am/Gori/Aprilia/SWM/Kramer/Puch 125cc engine eventualy(through the type 128/129 evolutions) became the basis of the the Aprilia RSW 125.

[evo550]

If we're not confining this to just vintage bikes I think the most recent offering of the KTM/BERG 300 2t would have to be one of the best engines ever to fire a shot! Power like a steam train yet could easily be ridden by anyone due to the amazingly linear deliver, its not so smooth it almost feels like an electric motor!!

I agree on this for the modern era.

Bingo !!
The Maico brigade are quite ?

[EML]

All the Euros are quiet except for Rotax, not too many Hondas getting a cap except little 4 strokes and the mighty CR500.
All of the Yams have gearbox issues
Most impressive are the rotary disc valve engines
Not many big 4 strokes getting a gong
Good thread though