Hi - Performance Cam for XJ Bikes

Im looking for any information on where to find a hi-performance camshaft for my 81 Seca 750.
I have seen some forums on here of people saying there bikes have been cammed - Anybody know where they are finding these camshafts?
Could they be taking cams out of a bigger engine?
Thanks for any info!

Lawnie

 

What they are talking about is changing the cam lobes to alter the valve opening duration and lift heights.

The real basics - a four stroke is called a 4 stroke because there are 4 phases. Isolate your view of the engine to one piston for a moment.

1) Piston travelling down - sucking fuel mixture into the cylander... Intake valve is open, exhaust valve closed.

2) Both intake and exhaust valves closed - piston compresses the fuel mixture on the up stroke.

3) Power Stroke - near the top of the stroke it sparks and pushes the cylander down with the force of the explosion. Both intake and exhaust valves closed

4) Exhaust Stroke - Intake valve closed, exhaust valve open.


The cam has lobes on it - these lobes open the valves in time with the pistons movement. Changing the shape of the lobe changes the height and the duration of the valves opening.

So - a cammed bike is a bike that has had its cams modified - either by altering the cam lobes or by balancing and reducing the weight of the cam shaft.

If for example you built the intake lobe up a bit you could make the valve lift higher for longer - allowing more gas to enter the chamber - more gas more bang more power.

That is as far as my cam knowledge goes... but I'm sure someone will time in with more detail to what they're doing to the cam lobes or if they're just balancing and lightening the cam... also I'm sure someone will know a shop that can do this for you. The true test would be a dyno of course.

 

Might be a bit of a problem finding performance cams for a bike this old. XJ's represent a very small market for performance parts, so I doubt anyone is making anything for your bike. If by chance you find something, it will likely create a very narrow powerband up near redline, with accompanying losses in low and midrange power, i.e. you will have to wring your bike's neck to be able to find and use the power unleashed by the cams, which is likely minimal anyway without extensive intake, exhaust, porting, rejetting etc. Not worth the time or money. Much easier to get a newer bike, or slot a 900 Seca engine into yours, if you can find one. There may be big bore kits available for that engine, but you would then be back into your original situation of trying to coax out power from an old design. If you want to go fast, there are an enormous number of newer or bigger machines that will do that at less than the price of a pile of engine work.

There is always the option of regrinding your cams, or degreeing your cams, but you have to know what you want, how much clearance you have to play with, where you want to make power etc.

 

I'd have to agree MacMcMacmac ( wow that is a lot of Macs ) -- it could be done but it's not cheap and you'd have to balance the cost benefits - it would certainly be a really cool maxim but it's going to cost more to do than a faster bike would to buy...

If you owned your own shop, or had a shop you could learn how to do this in - then this could be a *cheap* way to get into some interesting mods. If you do go this route really consider improving the oil system... more power is more stress.

 

http://www.webcamshafts.com/yamaha-moto.html#16
this place might be able to help? they add material and grind to specs your looking for

 

I think there is some good advise here.
I think I am going to leave good enough alone, The bike runs like a long tailed cat in a room full of rocking chairs anyway!
Sounds like I would be getting in way over my head.
Thanks for all the info guys!

Lawnie
PS. Im still looking for a good dash bezel for my 81 Seca....!
I would by the whole dash if I had to.

 

hello there you proebely noticed it my my post that said that the bike has been jetted up and cammed i my self would never pay what it would cost to have the cam worked up or re-fabbed. But the guy that did it is a certified yamaha mechanic and has access to just about any tool he needs and did the work him self so im sure it dident cost to much but normely to get a cam reworked it wil cost you about $800 on the cheap side if your luckey but usually right around 1800 to $2000 it about the same as have head work done. relly not hard to do if you know how and have the tools but expnsive to have done do to the tool's costing so much and the posibilty theay could haf to buy you a new head if theay mess it up

 

All most for got to add this info it's not relly cost effective to have it doen but maby some one you know would cut you a deal in return but then agin when changing the cam lob's you are relly messing with how the motor runs you could make up to 50% more power off from this but with more power comes more heat and heat is not somting you want on a air cooled engine. the came work i am refuring to is mild as to what could of been done he said the main thing that was changed was the lift witch in return changed the duration (exaust lob's) is what he said was the big change the intake wasent changed much at all his gole was a little more power and to keep it running cool and cleen

 

Megacycle has 5 cam grinds for these bikes, ranging from street stock to all out drag race, $388 a set, on customer cores. The bes one looks like either the 256-00 at .354 lift and 254 duration or the 256-30 at .375 lift and 257 duration, which needs aftermarket springs. The springs should be changed with a cam change anyway IMO. I used a set of Megacycle .410 lift cams in my Z1 several years ago and got great midrange power and upper end with no bottom end loss that I noticed. Gained about 12 hp with that mod. On our smaller 650's or 750's i wouldn't guess more than 5 -7 hp gain. Roughly about 15% at best. cruzerjd

 

There are a couple things you can do with the stock setup on that engine besides jet kits and pipe, but I only recommend doing these things if you are a skilled mechanic.
The cam sprockets bolt to your cams, you can use a dremel and E-longate the mount holes where they bolt to the cam, no more then 1/4 inch to either direction of the mount hole, keeping the circular pattern as to be able to rotate the sprocket. Definately before doing, scratch mark your stock tightened position as this is your baseline to start.

Understand that playing around doing this, is only going to shift your power and torque locations from your original Dyno curve. If you want more power at a lower rpm then what you have for better roll on freeway power, you can do that, but remember you'll loose that power higher up in the rpm range. This all takes a ton of $$ spent in and out of a Dyno Shop, so I only recommend people with access to this stuff or money is no object people bother with this.

Your engine's cam setup is pretty close to optimum from the factory for what that engine is going to produce.

The other is having about 3 thousands milled off your head, this will boost your compression from the stock 9.7-1 to over 10. but find a knowledgable shop for bike heads, that can give you exact #'s, Attack Yamaha in california was excellent with Yamaha Heads, as they provided the Yamaha's that were in the Superbike shootouts several years ago. I can't find a website for them, so I don't know if they still exist, but reputable performance places like Mr. Turbo, COPE Racing etc. would be good.
How unique that when I started Dragracing, the Seca750 was my first bike I ever dragraced, it's a great bike. Good luck

 

call a rep at edelbrock...they custom grind cams for just about any thing...you may have to sumit the spec.s from yours....but they are right... beef up the cooling system, and oil pressure may need a boost as well...

 

I was Boxing up the spare Engine for My 82 Maxim last Summer and realized the Intake and Exhaust Cam's are not identical. Same Duration, but the Intake Cam has around 4 to 5 Thousandths more Lift than the Exhaust Cam, but everything else appear's to be exactly the same. I've played around with it and there's no Clearance issue's as far as the Camshaft itself is concerned. Certainly I'm not the first Guy to consider Running 2 intake Cam's, has anyone every heard of someone trying it? I think it will work, unless of course it causes the Valve's to clash. Which I have considered that was the reason the Exhaust Cam has less Lift in the first place. But I wanna try it.

 

I have bought some cam gears for my XJ750 Maxim (1982) to eventually change the cam timing by milling the bolt holes for about 3 degrees +-. This will require a degree wheel and knowledge
As stated above it will not increase power but will shift the power band (curve) to a more usable RPM range I.E. low to mid RPM. It will feel torquey (made up word there) so you feel more power down low.
I bought a second set of cam gears (ebay) so if I don't like the mod I can always go back to stock.
Cheers, 50gary

 

Not true. It will likely increase power, simply shifting the peak torque rpm point up the rpm range will do this.
The question is, do you want a screamer or a puller? If your thing is revs and gearchanging then go for more overlap.
More overlap pushes the peak power point up the rpm range, up to a point.
Put simply, the more area under the valve opening duration curve, the more air goes in, the more torque you make, up to a point. So fitting inlet cams to the exhaust? Why not, but the gains will likely be small.
The other thing is, if you shift the “power band” too high up the rpm range, you will run out of airflow capability, so you then start sacrificing bottom end torque for nothing at the top end...

 

I've been doing a bit more Tinkering with My spare Head. Wanted to make sure more Exhaust lift wouldn't cause the Valves to Clash during Overlap and it appears to be a non-issue. The Intake has to be open almost 3/4 before the Exhaust Can touch it. And there is a pretty big difference between the 2 Cam's. If the Intake is at full Lift, the Exhaust Valve can open and close completely without Touching..

 

I'm also pretty sure if I put an Intake Cam on the Exhaust side I'm going to have to install it Timing mark down.

 

Yamaha was smart and put (relatively) hot cams into the Secas from the get-go. If you have a Maxim it's a straightforward swap to put a Seca cams in (though it's just the intake cam that's different). If you wanted a custom grind that's the cam I'd use for a core.

If you're going to use an intake on the exhaust valving then It'd be pretty easy to pop a new timing mark onto the sprocket, rather than flip it and perhaps not have the mark be exactly right. In fact if you're going to do anything with regrinding you'd want to check and perhaps remake the timing marks anyway. The factory ones are fine, but not exactly perfect.

 

If you’re determined to try to squeeze more power out of a 40yr old single valve design then sure, change the cam out. But you really need a dti and degree wheel, and some knowledge of cam timing basics. Then you can start trying different settings (on the bench with plasticine on the piston to check clearances at the extremes of adjustment).
If you end up with the two most radical stock cams, timed in for best power (ie the most bhp), then you might want to look at higher compression, and getting some valve work done to improve airflow. Can you get bigger inlet valves fitted?
This is engine tuning work that is beyond most shops, but can be done at home, if you are prepared to learn. (Except skimming the head, unless you have a milling machine ).
As someone who has spent 40 years modifying production engines, I can guarantee you that there is more power to be had from your engine. What I can’t guarantee is that you will be able to find it. I suggest Smokey Ynick or Dave Vizard books as good starting points for learning - before you make mistakes.
Oh, and if you think you’re making more top end power, you’d better make sure those pots are getting enough fuel, else you will end up walking around with a holed, white piston or two....

 

Holed pistons don't provide much power. Don't ask how I know.

 

I checked the 1982 horsepower output for the Seca 750 it stated 82hp, that's the same as my 82 750 Maxim? It sort of asks the question "if the Seca has a slightly hotter cam why isn't it reflected in a higher HP listing?"
Do you have any specs for this intake Seca Cam? I found one on EBAY for $25.00 looks to be good condition.
Cheers, 50gary

 

Because for the 750 engines, all of the air-cooled engines* used the same camshaft on the intake and the same camshaft on the exhaust (they are different shafts, but the same between engines......there is no "750 Seca specific camshaft")...........all of them EXCEPT for the 1984 XJ750RL Seca exhaust camshaft, which was different (but it was shared with the XJ700 air-cooled engines). Here are the goods:


HCP3841
OEM Intake CAMSHAFT 4K0-12171-00-00
Lift: .346" or 8.80mm
Duration:
Intake opens 38-degrees BTDC
Intake closes 58-degrees ABDC
Overlap: 74-degrees
Applications:
XJ700 air-cooled
XJ750 all air-cooled including XJ750RL
XJ750 Police (37H)



HCP3842
OEM Exhaust CAMSHAFT 4K0-12181-00-00
Lift: .307" or 7.80mm
Duration: not given
Overlap: not given
Applications:
XJ750 all air-cooled (except XJ750RL)
XJ750P (37H)



HCP3843
OEM Exhaust CAMSHAFT 22N-12181-00-00
Lift: .327" or 8.30mm
Duration:
Exhaust opens 56-degrees BBDC
Exhaust closes 26-degrees ATDC
Overlap: 74-degrees
Applications:
XJ700 air-cooled
XJ750RL



MODEL NAME: XJ750RL
STREET NAME: 1984 XJ750 Seca
MODEL ID CODE: 44X (Canada)
FRAME ID: 44X (Canada)
MODEL ID CODE: 45T (Australia)
FRAME ID: 45T (Australia)
SERIAL NUMBER STARTS AT: 000101
NOTE: All XJ750RL models feature an XJ750 engine in an XJ900 frame. Only 601 made for the Canadian market and just 286 made for the Australian market. Engine actually displaces 749cc (1cc larger than standard XJ750 models, which were only 748cc's) and uses a hotter exhaust cam, larger intake valves (= 34mm, or +1.00mm vs. standard XJ750 valves), different crankcase, cylinder jugs, and pistons/rings, the XJ900 type clutch assembly and middle gears set, as well as the strengthened 2nd gear set as used in the XJ650 Turbo, XJ750-X, and XJ900 models. It has been noted that all the Red/Silver XJ750RL models (Canada) seem to have black motors while the Blue/White models (Australia) have silver motors.

 

The first cam is a 38 plus 180 plus 58, equals 276 deg, 346 thou lift - quite a tame cam by any standards.
The second you can discount.
The last one is a 56 plus 180 plus 26, equals 272 deg, 327 thou of lift. The first, the 4k0 would be the best bet, but it’s marginal.
The next question would be, what are the thickest valve shims available? This dictates the maximum allowed to be ground from the base circle of the best cam - my guess would be you need 80 thou to make it worth the bother, but cams are complex, so would need to speak to a cam grinder to evaluate. Longer valves could help, if they exist off the shelf, expensive to buy as race specials, but then you only need 4...
If I was in a fictional one make xj 700 race series I would be looking for larger, longer valves, having the cams reground with a target of 290 to 300 degrees duration and 400 thou of lift.
Then fitting or cutting new seats, blending and lapping, stiffer springs.
Then cutting the piston crowns to allow clearance, with something like 50 thou off the head face to increase compression to 12 to 1.
The engine would need bigger carbs, maybe some opening up of inlet and exhaust ports, K&N air filters, bigger exhaust headers, and a 4 into 1 pipe.
An extra 20 bhp? Maybe...

 

The 750 models all got the same cams.

 

Thanks for that little bit of non fake news. I nearly bought the cam.
Cheers, 50gary

 

So I made a discovery that led Me to abandon this Project. Yes the Intake Cam has more Lift, but on further inspection I found that the Exhaust Cam actually has a little more Duration. I'm guessing this was done to improve Scavenging, and They went with less Lift to Improve Velocity Lower in the Rev range where a 2 Valve Engine Shines. I've concluded that an Intake Cam on the Hot Side will Reduce Overlap and Kill Velocity, and I will See a Significant Loss in Power if the Bike even Runs..

 

Of course it would run. Maybe a little hotter, but it would be small differences. Velocity is built in with the exhaust ports. Ie it goes out with a bang. You have come up with theories to reason why the makers did something forty years ago - fair enough, but it's guesswork really.

 

Could this be of any help? From Megacycle Cams, San Rafael Ca.
CAM VALVE DURATION LOBE INTAKE OPEN/CLOSE RUNNING
NUMBER LIFT AT .040" CENTERS DESCRIPTION AND APPLICATION EXHAUST OPEN/CLOSE CLEARANCE
256-00 .354" 254° 108° OK with stock pistons and springs. Good 19 btc/55 abc .005"
.354" 254° 108° mid-range. Some top-end. Best in stock motor. 55 bbc/19 atc .007"
256-30 .375" 257° 108.5° Should clear stock pistons, but must check. 20 btc/57 abc .005"
.375" 257° 108.5° Best all around road race. Must use #106-Y. 57 bbc/20 atc .007"
256-40 .410" 250° 105° Drag race. Mid-range torque. Great throttle 20 btc/50 abc .005"
.410" 250° 105° response. Use racing pistons and springs. 50 bbc/20 atc .007"
256-20 .417" 268° Road race. Best for top-end. Use #106-Y + 12:1 or more compression.
256-60 .438" 258° Shim under! Drag race. Use #106-Y + 12:1 compression.
Stock .335" 236° Stock XJ-650 for your reference.
.305" 232°
YAMAHA XJ-900 SECA 4-cylinder (1983—1984)
Hardfaced cams, per pair, on customer cores.
CAM VALVE DURATION LOBE INTAKE OPEN/CLOSE RUNNING
NUMBER LIFT AT .040" CENTERS DESCRIPTION AND APPLICATION EXHAUST OPEN/CLOSE CLEARANCE
262-00 .375" 257° 107.5° OK with stock pistons and springs. Street and 21 btc/56 abc .006"
.375" 257° 107.5° road cam for improved mid-range and top-end. 56 bbc/21 atc .007"
262-10 .410" 250° 108° Must use modified pistons and springs. Race 17 btc/53 abc .007"
.410" 250° 108° only. Racing pistons and springs needed. 52 bbc/17 atc .008"
Stock .343" 240° 108° Stock cams for your reference. 12 btc/48 abc
.326" 236° 108° 46 bbc/10 atc

Cheers, 50gary

 

"Hardfaced cams" - I wonder if he built them up with welding rod? That would mean they are steel of sorts. Perhaps I'll try one, I think I have s knackered one here somewhere. Then of course I'd need to get it ground.....

 

No Sir, it has a significant impact. Because the Exhaust Port is much Smaller than the Bore the Gas's have to be Condensed/Compressed to Pass through. Compressing the Gas causes it to Speed up. And because the Valve determines the Size of the Hole the Gas is forced through, it determines exactly how much it needs to be compressed initially which has a huge impact on the Gas's Velocity exiting the Engine... The Exhaust Valve Creates the Velocity that then Builds as it Pass's through the Port.

 

Now for the Cams, as I said the Exhaust Cam has a little less lift, but a little more Duration than the Intake Cam, this means its going to stay open longer. It does this so it's still slightly open when the Intake Valve Opens, this is called overlap. It causes a Scavenging effect where the exiting Exhaust Gas's actually help draw the A/F Mixture into the Combustion Chamber. The Intake Cam will cause it to Open more but close Faster, and if the Exhaust Valve has already Closed when the Intake Opens You're not going to get that Scavenging effect causing a major loss of Power, and it's probably gonna Run like Sh*t...

 

No, they are a finished product, buy and install. Megacycle Cams has been around for years. This is not a backyard business.
Cheers, 50gary

 

Finished product or no, they are based on customers cores - ie reground after hardfacing - this from your post -
"Hardfaced cams, per pair, on customer cores."

@Jerrod Robinson1086 - your theory on thermodynamics and combustion and cylinder heads needs some work. Your definition and explanation of scavenging effect is correct though, but with the difference in numbers on the standard cams the effect will be tiny, hence my assertion that it would run, albeit slightly hotter, maybe.

 

I uploaded the pic from megacycles online brochure - sure they are welded up standard cams, but they are not a backyard outfit as @50gary says. Hopefully the pic makes their options clear. Note they don't have a spec for the standard 700 exh. Cam.
One other thing to note is they use 40 thou as the measuring clearance, which is why their numbers are less than quoted by the factory. Oh, and also in my earlier post commenting on @chacal s listing of cams my mental arithmetic let me down - the 700 exhaust cam has 262, not 272 degrees duration. Ie it is substantially less than the intake cam. So, want more power, fit an intake cam, or have your cores reground, or hardfaced and reground for more still. But if you go to these lengths you want to be gas flowing your head.
Oh, lastly, the frame above the xj cams is for the xs - that had more lift and duration if the info is correct, with the exhaust having more of both - do these fit in an xj head??

 

XJ700 air-cooled and xj750RL (1984) used the same exhaust cam, specs here:

OEM Exhaust CAMSHAFT
22N-12181-00-00
Lift: .327" or 8.30mm
Duration:
Exhaust opens 56-degrees BBDC
Exhaust closes 26-degrees ATDC
Overlap: 74-degrees
Applications:
XJ700 non-X
XJ750RL


They also used a 1mm larger (34 vs 33mm) intake valve than the XJ650/XJ750 engines; exhaust valve was the same as the 650/750 models.

So, to summarize for the air-cooled engines (700 engines vs. the 650/750 engines):

- have the same intake cams
- 700 has a larger intake valve
- have the same size exhaust valves
- 700 has an exhaust cam with significantly greater lift (8.30 vs 7.80mm) than the 650/750 engines


And as long as we are comparing YICS cylinder heads (1982-up 650, all air-cooled 700, all air-cooled 750), they are all the same casting number, so basically all the same head but the intake valve pocket opened up on the 700's ----- and I don't know whether any other changes were done to the intake or exhaust port shape, etc.

P.S. Megacycle has been in business for a long time, so I'll have to assume they know what they're doing.

 

Thanks for that @chacal , confirms its a lesser timing cam than the intake. How available are the 700 intake valves?
No one's questioning Megacycle cams heritage or ability here...