XJ650RJ (Seca) Valve CLearances.......

In studying oh-so-carefully my tattered and torn Haynes manual for the XJ650/XJ750 models, I come across a curious spec and was wondering if anyone had any insights.........

It seems that ALL XJ550/650/700 non-X/750/900/1100 models use the following valve clearances:

Intake: 0.11 - 0.15mm
Exhaust: 0.16 - 0.20mm

EXCEPT for the 1982 XJ650RJ model, which uses a different Intake valve clearance specification:

Intake: 0.16 - 0.20mm

That's quite a huge difference, and is the same as the exhaust valve clearance spec. I can understand why exhaust valves have more cold clearance built into them.....the exhaust valves heat up more, expand more, so they need more cold clearance to compensate. But why the huge clearance on the intake side, and for just this one model (actually, Haynes also says that the XJ650 UK models also use this increased intake valve clearance spec too).

Since the 650RJ shares the same valves, shim bucket, shims, etc. as all the other models, I was wondering if the above clearance specification is correct, or one of the infamous Yamaha Factory Manual/Haynes "we just copy what the factory says" mis-prints.

Any thoughts?

 

I checked the XJCD service supplement for the XJ650 Seca and it is 16-20mm for both intake and exhaust. Can't answer why.

 

This post is timely!! I've recently been thinking that those specs are not ideal! I adjusted my valve shims this past summer to RJ specs and the performance dropped and added a lean pop during decel. I'm going to try the other specs this coming summer - you know, cus I can.

 

This gets stranger and stranger. In my copy of the Haynes manual, page 31 says that the XJ650J and XJ650(UK) has the following valve specs:

Intake: 0.16~0.20mm
Exhaust: 0.16~0.20mm

The factory sticker inside the left side cover on the bike gives these specs:

Intake: 0.11~0.15mm
Exhaust: 0.16~0.20mm

The Yamaha XJ650J Supplementary Service Manual (dated 02-87) specs follow the specs printed on the sticker inside the left side cover on the bike. So I don't know where the Haynes people got their info. I think I'll go with the Yamaha dope especially since Fraps posted his experience. But why does my Haynes call for the odd spec on the XJ650J and in chacal's Haynes it shows that spec for the XJ650RJ?

Cheers,

Phil

 

Phil, that sticker on your cover should be the correct specs. I don't know why the 650 Seca would use different intake clearances than every other single Yamaha engine in the same engine series.

 

Hi chacal,

Yeah that bothered me too. I think I'll stick with the Yamaha specs on this one. As soon as I recover from that last parts order I want to order a copy of your Yamaha manual. That fuse box really did the trick!

I should be in good shape to ride the thing now when the weather gets better. Its showing +4 with a wind chill of -15 so I'm still hibernating! I want to ride it for a couple of weeks just as it is so I have some sort of before to compare the after with.

More later,

Phil

 

Oh man! I just setup mine using those wrong specs from the Haynes manual. Oh well, it is running pretty good.

Bruce

 

0.11 ~ 0.15 Intake and 0.16 ~ 0.20 Exhaust.

 

I remember it this way from 25 years ago...4-6 6-8 thousandths! Easier to rmemeber this way.

 

Yeah, I think the consensus is that, once again, the Haynes manual and the original Yamaha service manual (at least the version on the XJCD) is wrong....what a surprise!

 

the more clearance the longer the valve stays on the seat, transferring heat
read that someplace once, i guess it makes sense, but it can't make much differance

 

Too little clearance and the valve doesn't sit on the seat at all. Valve doesn't cool, plus it gets heated on the back too as the buning gasses blow past it. Lowers compression.....causes infertility, dandruff, heartbreak of psoriasis and all kinds of other bad things.

 

This has me thinking. I have 2 haynes manuals supposedly identical but one has obviously more detail - evident in the pictures at least. I'll have to see what it says about the valve specs. I remember thinking - how can the RJ have the same intake and exhaust specs while every other XJ listed has differing specs? Oh well, we'll see this summer.

 

Hmmmmmmmmmmmmmmmm, we might try comparing print dates and ISBN numbers. My Haynes was printed in 1994 and the ISBN is:

1 85010 353 4.

Anyone have any different numbers on their Haynes manuals?

Cheers,

Phil

 

Glad I saw your post. I have the same manual as you. I have my valve cover off now and checked the clearances. When I looked at my Haynes manual I also questioned the intake clearances.

My clearances are as follows:
Intake .10 .11 .13 .08
Exhaust .18 .20 .18 .18

If I follow the Haynes manual where the range of clearances for both intake and exhaust states .16-.20 all my intake valves are tight.

If I follow the consensus of the correct intake range being .11-.15 I have two tight valves.

I don't have a sticker inside my left side cover (the one you take off to crank the engine over, right?)

I think I'm going to go with the .11-.15 intake range. Comments?

 

The sticker might be on the inside of the right side cover.

But etiher way, trust me, the info on the stickers for all US model XJ650 models is the .11-15mm for the intake, and .16-20mm for the exhaust.

Whew! Better set those clearances to spec right away!

 

I tend to agree. I just checked one of my favorite resources, the Yamaha factory parts fiche. The XJ650J and RJ use the SAME CAMSHAFTS. I could see the clearances being different if they used different cams but they don't. Gotta be a perpetuated typo.

 

Thanks Chacal - Got my parts order. Everything in great shape. The valve shim tool worked great. I'm sending you an order for the shim I need, now that I know what the right clearances should be thanks to this post!

 

I trust you guys completely, so much so I called Yamaha America today. :wink: :lol:
They tried to have me call the local dealer but, after some conjoling I ended up speaking with 3 reps and an engineer.
Yamaha America says THE FACTORY MANUAL IS WRONG.
.11-.15 is the correct intake clearence for an XJ650RJ.
NOT .16-.20, this is the exhaust clearence.

So I'll be doing the shims again. :roll:
It's really not the shiming that bothers me, it's the synching and chopping, that I worked so hard on last year to get right that pisses me off. :evil:

Before I called Yamaha I was at the shop getting the bike inspected and put the question to the guys.
The most interesting answer was that, in the old Honda CB-F's it was recomended to loosen up the intake clearence to improve power at higher rpms.
Just about everyone agreed that on a 27 year old bike you wouldn't be able to tell the difference anyway.
What do you guys think about the last two statements?

 

Yes, the factory manual is wrong, and the sticker inside the side cover is right, and Yamaha actually issued a tech service bulletin early in 1982 to notify dealers that the service manual is wrong..........

But how in the world you ever got past the receptionist at Yamaha is one of those ethereal things that are truly unknown and unknowable. Perhaps you should have bought a Super-Lotto ticket today also...........

How would loosening the valves (= more clearance?) help power at higher rpm's? What was their theory regarding this technique?

 

There were alot of people talking but, I will try and explain it the best I can.
The theory was:
This would be for timing.
On the old metric bikes the cams were not adjustable in degrees.
So having the intake valves open later would improve Hp at high rpms.
It seemed to me that extending the duration a valve was open or advancing the timing might have an effect on Hp.
This would retard the timing if I understand correctly.
I find that if I'm not 100% sure that I'm correct, I don't challenge guys who have been around bikes there whole life.
Getting schooled at the shop in front of a crowd is no fun.
That's why I asked you folks what you thought.

 

Well, loosening the valves (increasing clearance) would not give more DURATION, it would give less (duration is the total amount of crankshaft rotational degrees that the valve is lifted of its seat---or, in other words, in contact with the camshaft and being actually rasied by the camshaft).

Increasing the clearance means that the camshaft would have too move that much further, rotationally, before it began to LIFT the valve up, and would also set the valve back down onto its seat (fully closed) earlier.

So larger clearances would REDUCE the duration.

However, given that cam lobe profiles tend to be one of increasing the lift RATE after the first few degrees of contact---in other words, the lobe is profiled to give a "gentle" amount of lift at first before it rockets the valve to it's fully open position, and vice-versa on the closing side----by increasing the clearance, you have changed the rate at which the valve opens, and that rate is, deep in the dark bowels of the art-science that is cam and combustion and cylinder head design, one of the "tuning factors available to camshaft engineers.

Changing the clearances would, indeed, change the valve opening (and closing) TIMING, as that is the definition of when the valve starts to open in relation to where the piston is BTDC. If you increase the clearance, the valve opens a bit later, and thus the piston is that much closer to TDC.


Now, perhaps by increasing the clearance on the intake side (this decreasing the duration that the valve is open, but changing it's opening rate----once it finally started opening, that is!-----to a quicker rate) while at the same time making a similar or OPPOSITE change in the exhaust valve clearances-----or, maybe doing the exact opposite------would now allow you to explore the benefits of changing the valve OVERLAP, which is the amount of time (rotational degrees "time", that is) that both the intake and exhaust valves are open at the same time.

These are all tuning "tricks" that, like re-jetting for pods, could be explored on a trial and error basis.

Or just cut new cam profiles and experiment.


In this realm, it really helps to have a room-full of flow benches, trained theoretical and practical engineers, and lots of computing and graphical design power and intelligence available to be able to run lots and lots and lots of simulation trials.

Electronic valvetrains, where you can change all these types of factors (as well as valve overlaps, total lifts, lift profiles, etc.) are really swell to have when you start messing around with these sorts of things!


This is the kind of stuff that Top Fuel drag racers, Formula 1 engine designers, and Superbike builders really get wood over.........or, if they are not successful at it, get migraines and "Fired!" over........ 8O

 

Thanks Chacal that made it a little clearer as you could tell I thought this would reduce duration, which it does, and could not see the benifit.
Makes me feel a bit better to know people at the shop aren't just talking out there a$$ to me because they feel I won't understand.
Still as an answer to why Yamaha would have set the intake clearence looser, it's pretty good theory. :wink:

 

Honestly I don't think "loosening the clearances" will improve high-rpm power in most cases; maybe there was something about the cam profiles on the CB-F series that made sense for that bike but in general I dunno...

 

I had to though a new post on here in case someone like me is doing their valve clearances for this spring. I only decided to check to make sure I using the correct specs because chacal's chart with the valve shim tool didn't have a provision for the JX650J model. :?

Well I have to say xjbikes search worked awsome for me again!!!
The first thread I clicked on was this one and man am I glad I did...

Thanks again guys,
James