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