Anyone used or using a 250-30 megacycle cam for 750?

staggers

XS650 Enthusiast
Messages
69
Reaction score
5
Points
8
Location
Brisbane, QLD, Australia
Hi all,

I'm wondering if anyone is using the Megacycle 250-30 cam?
They say it needs piston and valve guide modifications!? Anyone know what specific modifications are required?


Cheers
 
I've used them in race engine with excellent results. It will easily support 70 RWHP in a well-prepared engine with proper port work. The Megacycle web site says that you must cut .080" off the guide length. It's isn't a big deal, any machine shop can do the work.
The cam itself is a bit too much for an otherwise stock engine. While not really rough on the valve train, it is more aggressive than their 20 or 00 street cams. The 40 should not be used on a street engine; it will wear your valve train too quickly.

The vintage Shell #1 cam works well on a 750 street engine and can be sourced from Hoos Racing. It's good for up to about 64 - 65 RWHP in a well prepared engine with a decently ported head. All these cams like compression, but with today's fuel, I'd keep it under 10 - 1 and no more spark lead than about 34.

You'll need upgraded valve springs, a free exhaust, clean up the flashing in the ports and, preferably a set of 34mm round slide Mikunis. I say "preferably" because they're big enough for what you're doing, they're cheaper than flat slides, they are simple and there's a ton of information out there for jet sizes, etc. to get you going.

Good luck.
 
As xs650 said great race motor cam, We make 70hp with it. You will need to cut the .080 off the guides or I have Kibbblewhite that are already done. Which if I was going that big I would also put in the bigger valves and do some porting to get the most out of the cam. You can pm me for prices if you decide to go that way.. To get the 70hp we run 10.5-1 pistons with big valve pockets to handle the larger valves we use.
 
I run one in mine valve guides are a must I bought a second hand top end with standard guides, I wondered why there was no valve seals fitted until after I fitted some and found they were being hit, I have run mine with both Wiseco and Hooses JE pistons the JE are much better,
I don't ride mine on the road, but from riding at slow speeds through the pits would say it would be rideable,
I run Dellorto's on mine and have recently increased the intake length to around 4" with a 36mm to 34mm taper, this has increased top speed over the quarter by around 5mph fastest time last time I rode it was 12.18 at 110mph
 
Cheers for that, great info :thumbsup:

My goal is to make a strong, torquey and reliable motor for the street.
I'm not aiming to get max power figures but 65-70 would be great!
Even if it isn't all that smooth to ride, at least it will have a bit of mongrel in it that'll keep a smile on my dial :laugh:

Going 277 as well

Head porting is another thing I need to know more about? as I hear even the pros stuff it up on these heads! I read of D-porting and all sorts on this site, what do you guys recommend for the modified street motor?
 
Because the stock ports are, even for a 750 kitted engine, slightly too large to begin with, you can't really remove any metal unless you really know what you're doing. Even small mistakes can reduce performance by slowing gas velocity down and/or negatively affecting where turbulence occurs.

If you simply remove the flashing in the ports and match the intake manifold to the head so there's no ridge(s) to speak of, that should get you some free power. Again, if you know what you're doing you can fit oversize valves and open up the pockets a bit.

EDCO (Enginedynamics.com) in Petaluma, California does a good job on these heads. And, Hoos Racing apparently offers race tested modified heads. Check them both out.

If you have the cash Michael Morse at 650 Central can sell you a CNC copy Lillie head (an exact copy of the head on Steve Eklund's AMA race winning XS750) which works very well on the street or race track and can support up to 73 rear wheel horsepower.
 
Thanks 650performance, I appreciate your help :thumbsup:

I think for now I'll go with your 1st option just clean up the flashing and match the inlet to manifold
You shouldn't have told me about the Lillie copys haha, now I'm researching the hell out of them.
They are expensive! But I guess if I were to get a professional to vapor blast then port the stock head, machine and install bigger valves, machine the valve guides and put it all together, taking the risk he/she has done it right? Would probably cost me at least 2/3 of the lilly head anyway at least in Australia anyway!? Not to mention the gains probably wouldn't be as good as the lilly in the 1st place?
So I think the lilly option isn't so silly after all :D
 
You'd be surprised what can be achieved with the stock head in the right hands. Get with HotDog look up his long rod build and PM'em.
 
Because the stock ports are, even for a 750 kitted engine, slightly too large to begin with, you can't really remove any metal unless you really know what you're doing. Even small mistakes can reduce performance by slowing gas velocity down and/or negatively affecting where turbulence occurs.

If you simply remove the flashing in the ports and match the intake manifold to the head so there's no ridge(s) to speak of, that should get you some free power. Again, if you know what you're doing you can fit oversize valves and open up the pockets a bit.

EDCO (Enginedynamics.com) in Petaluma, California does a good job on these heads. And, Hoos Racing apparently offers race tested modified heads. Check them both out.

If you have the cash Michael Morse at 650 Central can sell you a CNC copy Lillie head (an exact copy of the head on Steve Eklund's AMA race winning XS750) which works very well on the street or race track and can support up to 73 rear wheel horsepower.

Just wondering if these Lilli CNC replicas are a copy of a Lilli OU-72 or a modified standard head?
I read up on the OU-72 heads and seems they have a higher stack and lower valve cover? And use shorter rockers than stock?? Is that right?
Would the Lilli CNC head require those shorter rockers too?

Cheers mate
 
Last edited:
using a heidens 277 camshaft which he says is same as a m/cycle 250-20 ,found it to be a very nice cam through all the rpms but never found that real cam oomph so emailed jerry and asked what rev range it should be..normal disclaimers depending on carbs /exhausts etc but says about 8000 revs so if the 250-20 cuts in there hate to think what the 250-30 would be like ,could be fairly useless for street use ,mines 750 kit,34vm carbs ,worked head ,hi ratio gears etc etc ,if had the choice again would most probably gone for a shell 1 grind but cleaning up the head really worth while
 
Let's all so set the record straight for the last time I hope..it is OW-72..not OU, When I went out to buy Shells business he had 2 stilling in the shop. I asked what he wanted for them and he said $7000.00, I wish now I had them. Thanks Gary
A little history
Sold on Bill of Sale
  • Shell 750 cc Yamaha Racing engine
  • Flatslide carburetors
  • One of about 30 Factory OW 72 Yamaha Racing engines built
  • Shell Thuet chassis and swing arm
  • Built by Shell for Factory Yamaha effort
  • Kenny Roberts flat track racer
  • Later ridden by Hank Scott and Wayne Rainey
  • Shell pipes
  • All components period correct and in as raced condition
  • Engine # 447-711664
  • Sold on Bill of Sale
  • Shell 750 cc Yamaha Racing engine
  • Flatslide carburetors
  • One of about 30 Factory OW 72 Yamaha Racing engines built
  • Shell Thuet chassis and swing arm
  • Built by Shell for Factory Yamaha effort
  • Kenny Roberts flat track racer
  • Later ridden by Hank Scott and Wayne Rainey
  • Shell pipes
  • All components period correct and in as raced condition
  • Engine # 447-711664


In the 1970s, the AMA National Championship motorcycle races were among the most keenly watched sporting events in the U.S., thanks to movies like “On Any Sunday” and television coverage of the racing season. As such, racing was an excellent advertisement for the factories, who were willing to invest tidy sums in engine and chassis development, as paychecks for star racers. The biggest star in ’76 was ‘King’ Kenny Roberts, who held the No. 1 plate for two years prior and was eager to retain his crown again. Roberts rode for Yamaha whose street-based XS650 engine was the basis for the company’s flat track racer, competing against the pure competition Harley-Davidson XR750. As H-D squeezed more HP from its V-twin, Yamaha tuners like Shell Thuet bumped against design limitations of the production XS650 cylinder head, halting at around 70 HP, and Kenny Roberts was not amused. Roberts had Shell Thuet fired as Yamaha’s tuner, and brought Tim Witham, owner of S&W Engineering, out of race retirement in hopes he could extract more power. Witham addressed the cylinder head issue directly, by designing a totally new head, which he estimated should make 90 HP, 5 more than the XR750. Yahama cast 25 of the entirely new heads for homologation as a new model. The factory sent machined but bare castings to California in batches, and Kel Carruthers built up running engines as required by the AMA, and even installed a racing engine in a fully road-legal machine. The new model was dubbed the OW72, and did indeed produce far more power than the street-based XS650 was capable of. The 750cc OW72 was serious competition for the mighty H-D XR750, winning plenty of races under Kenny Roberts, Hank Scott, and Wayne Rainey. This 1976 OW72 was Kenny Roberts’ racer, built by Kel Carruthers with the Witham cylinder head. It was later raced by Hank Scott, and Wayne Rainey, and features flat slide carbs, a Shell Thuet racing chassis, swingarm, and pipes. This OW72 is effectively a factory Yamaha dirt-track racer, built specifically for Kenny Roberts to retain his No. 1 plate. All components are period correct and in as-raced condition, and the engine number is 447-711664. Kenny Roberts declared this OW72, “the best thing I ever rode.”
 
Interesting read on the ow72. I wonder after that effort and result why Yamaha decided not to continue with the racing effort.
 
Here is some Yamaha racing engine info. OW72 Article in the Aug 76 cycle world.
Link; https://thexscafedotcom.wordpress.com/tag/racing/

I'm confused about Shell Thuets involvement with the OW72 head and engine and the modified frame for the race bike, (as per the quote from that sale of the bike in post #11)..

If Shell had been fired and the development done to the frame was by someone else, (as per Cycle world article on the OW72), how is it an AMA Kenny Roberts OW72 Race bike ridden by Kenny Roberts in 76 can be sold as a Shell Thuet frame when the frame isn't his.
 
Let's all so set the record straight for the last time I hope..it is OW-72..not OU, When I went out to buy Shells business he had 2 stilling in the shop. I asked what he wanted for them and he said $7000.00, I wish now I had them. Thanks Gary
A little history
Sold on Bill of Sale
  • Shell 750 cc Yamaha Racing engine
  • Flatslide carburetors
  • One of about 30 Factory OW 72 Yamaha Racing engines built
  • Shell Thuet chassis and swing arm
  • Built by Shell for Factory Yamaha effort
  • Kenny Roberts flat track racer
  • Later ridden by Hank Scott and Wayne Rainey
  • Shell pipes
  • All components period correct and in as raced condition
  • Engine # 447-711664
  • Sold on Bill of Sale
  • Shell 750 cc Yamaha Racing engine
  • Flatslide carburetors
  • One of about 30 Factory OW 72 Yamaha Racing engines built
  • Shell Thuet chassis and swing arm
  • Built by Shell for Factory Yamaha effort
  • Kenny Roberts flat track racer
  • Later ridden by Hank Scott and Wayne Rainey
  • Shell pipes
  • All components period correct and in as raced condition
  • Engine # 447-711664

In the 1970s, the AMA National Championship motorcycle races were among the most keenly watched sporting events in the U.S., thanks to movies like “On Any Sunday” and television coverage of the racing season. As such, racing was an excellent advertisement for the factories, who were willing to invest tidy sums in engine and chassis development, as paychecks for star racers. The biggest star in ’76 was ‘King’ Kenny Roberts, who held the No. 1 plate for two years prior and was eager to retain his crown again. Roberts rode for Yamaha whose street-based XS650 engine was the basis for the company’s flat track racer, competing against the pure competition Harley-Davidson XR750. As H-D squeezed more HP from its V-twin, Yamaha tuners like Shell Thuet bumped against design limitations of the production XS650 cylinder head, halting at around 70 HP, and Kenny Roberts was not amused. Roberts had Shell Thuet fired as Yamaha’s tuner, and brought Tim Witham, owner of S&W Engineering, out of race retirement in hopes he could extract more power. Witham addressed the cylinder head issue directly, by designing a totally new head, which he estimated should make 90 HP, 5 more than the XR750. Yahama cast 25 of the entirely new heads for homologation as a new model. The factory sent machined but bare castings to California in batches, and Kel Carruthers built up running engines as required by the AMA, and even installed a racing engine in a fully road-legal machine. The new model was dubbed the OW72, and did indeed produce far more power than the street-based XS650 was capable of. The 750cc OW72 was serious competition for the mighty H-D XR750, winning plenty of races under Kenny Roberts, Hank Scott, and Wayne Rainey. This 1976 OW72 was Kenny Roberts’ racer, built by Kel Carruthers with the Witham cylinder head. It was later raced by Hank Scott, and Wayne Rainey, and features flat slide carbs, a Shell Thuet racing chassis, swingarm, and pipes. This OW72 is effectively a factory Yamaha dirt-track racer, built specifically for Kenny Roberts to retain his No. 1 plate. All components are period correct and in as-raced condition, and the engine number is 447-711664. Kenny Roberts declared this OW72, “the best thing I ever rode.”

Great little bit of history there Hooser.
Yeah I did notice people call them OU or OW's but I'll take your word for it that OW is correct.

I was trying to find out on my last post if the Lilli copy CNC head from XS650 central was a copy of the OW-72 head or is it based of a standard head that Harry Lilli modified?
 
Great little bit of history there Hooser.
Yeah I did notice people call them OU or OW's but I'll take your word for it that OW is correct.

I was trying to find out on my last post if the Lilli copy CNC head from XS650 central was a copy of the OW-72 head or is it based of a standard head that Harry Lilli modified?
It is a copy of the standard xs650.
 
Also reason Yamaha pulled the plug was they could not win, they went where they could as well as Roberts over to Europe and Road Racing where the money was.
Here is some Yamaha racing engine info. OW72 Article in the Aug 76 cycle world.
Link; https://thexscafedotcom.wordpress.com/tag/racing/

I'm confused about Shell Thuets involvement with the OW72 head and engine and the modified frame for the race bike, (as per the quote from that sale of the bike in post #11)..

If Shell had been fired and the development done to the frame was by someone else, (as per Cycle world article on the OW72), how is it an AMA Kenny Roberts OW72 Race bike ridden by Kenny Roberts in 76 can be sold as a Shell Thuet frame when the frame isn't his.

The frame was Built to his specs, even though Yamaha designed the ow-72 there was a lot of extra work going into them after that buy Shell and others.
 
using a heidens 277 camshaft which he says is same as a m/cycle 250-20 ,found it to be a very nice cam through all the rpms but never found that real cam oomph so emailed jerry and asked what rev range it should be..normal disclaimers depending on carbs /exhausts etc but says about 8000 revs so if the 250-20 cuts in there hate to think what the 250-30 would be like ,could be fairly useless for street use ,mines 750 kit,34vm carbs ,worked head ,hi ratio gears etc etc ,if had the choice again would most probably gone for a shell 1 grind but cleaning up the head really worth while
The 250-00 would be a better cam for street and pull harder up top than the shell. If you want the OOMPH,go flat slides 3 to 4 inch spigot manifolds really work the head and step the headers,why no one offers these types of headers is beyond me, it;s the perfect balance for bottom end while not choking off top end pull performnace
 
The 250-00 would be a better cam for street and pull harder up top than the shell. If you want the OOMPH,go flat slides 3 to 4 inch spigot manifolds really work the head and step the headers,why no one offers these types of headers is beyond me, it;s the perfect balance for bottom end while not choking off top end pull performnace
step the headers??
 
Simplest approach first 6 to7" 1 1/2" straight shot to first radius turn of 1 5/8" to second radius turn final straight shot 1 3/4". You could also add in a balance tube for more low to mid range performance. Also the inner tube steps where welded act as a anti reversion,kinda hard for a lower negative pressure backing up to re enter a higher pressure point.
 
Back
Top