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Author Topic: Yam RD "Blue Dream"- Ride,Maintain,Tune  (Read 47074 times)

Offline jpmobius

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #240 on: May 25, 2016, 10:39:50 »
The heads you have are very hard to seal.  O rings are the way to go as you can machine a flange into the heads to match the recess in the cylinder which will center the head in the cylinder.  The stock arrangement allows for a very sloppy fit and makes accurate squish clearance impossible.  With the centering step in the head you can then simply cut a groove for the o ring and you have the best situation possible. 
Yamaha changed the gasket design when they made the 400.  It is the same as your 250 where the gasket surrounds the head bolts.  This is not needed at all for sealing the combustion chamber, but does allow for tightening the bolts without bending the head so much.  On your 350, the bolts are outboard of the gasket.  When you tighten the bolts, it bends the head over the gasket which causes the head to bow upwards in the center between any two bolts and thereby looses clamping pressure on the gasket.  Of course the result is leaking.  This gets worse using the early heads which have the inside cooling fin interrupted for the bolts, and much worse when you machine the heads making them thinner.  And of course even worse when you improve the chamber and squish increasing the pressure.  And of course, more torque make the problem worse, not better!  So you can see you have your work cut out for you - very difficult indeed to get these heads to seal. 

But with some determination and more than a bit of luck you may see success.  Try this.  Get a piece of glass and some #400 wet sandpaper and carefully lap the sealing surface of the heads.  Probably you will easily see they are bent.  Just make them flat removing as little material as possible, but don't leave a trace of a low (high) spot.  Anneal the gaskets as a last step before you install them.  Copper work hardens very rapidly which will happen with any cutting, filing or bending.  Make sure they are perfectly flat before annealing, and don't flatten them out if they curve a bit when you anneal - let the head flatten them when you install them.  After annealing, spray them on both sides with copper gasket sealer like permatex copper-coat.  Let them dry, and then give them another light spray right before you install them.  Torque the head bolts VERY carefully in three stages up to spec (do not exceed 20 lb-ft under any condition!!!!  I think the factory spec is 16 lb-ft).  Excess clamping pressure will absolutely cause the gasket to leak!  Run the engine up to temp and let cool down completely and re-torque.  Then take a very easy ride just long enough to bring the engine up to full temperature, let cool completely and re torque.  Repeat the ride and cool down and re-torque.  If the head bolts do not need additional tightening to achieve the torque value, take the bike for a long easy ride and check again.  Once the torque values are maintained you should be good to go, but don't be surprised if the heads start to leak again if you ride like a madman!  This tedious regimen has worked well for me on well tuned engines with the stock gasket set up - good luck!
« Last Edit: May 25, 2016, 10:44:27 by jpmobius »
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0

Offline TranceMachineVienna

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #241 on: May 25, 2016, 11:00:58 »
Yamaha changed the gasket design when they made the 400.  It is the same as your 250 where the gasket surrounds the head bolts.  This is not needed at all for sealing the combustion chamber, but does allow for tightening the bolts without bending the head so much.  On your 350, the bolts are outboard of the gasket.

Thanks for your advice!

Youre expertise is completely right, i never had sealing issues with my stock RD250F head gaskets, whatsoever.
I will try the new headgaskets,follow your instructions and O-Ring will be a winter project,possibly with a better combustion design to come too (still have the completely stock RD350 heads on my shelf to work on).

Since my mains look like they are spot on:Should I mess with the needle position in any way,how will this affect the mid range of the engine performance?

Offline jpmobius

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #242 on: May 25, 2016, 11:19:44 »
You will just have to experiment with the needles.  Be sure to adjust the pilot air for off-idle performance as a part of fooling around with the needles.  You could potentially even want to change pilot jets if you want to "fix" something you don't like off-idle.  You can spend a LOT of time fooling around with different needles (and all the rest of the adjustable parts) and not find perfection.  Sometimes I think it is better to have a campaign geared to having as few undesirable characteristics as possible instead of requiring perfection across the board!  A lot depends on how you ride.  If you blast around all the time you won't notice that it carburets less well when going slowly and vice versa.  Sometimes it can be quite challenging (impossible?)to get really good performance for both situations, so just fool around with it until you like how it drives the way you usually ride.
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0

Offline TranceMachineVienna

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #243 on: May 25, 2016, 11:28:58 »
You will just have to experiment with the needles.  Be sure to adjust the pilot air for off-idle performance as a part of fooling around with the needles.  You could potentially even want to change pilot jets if you want to "fix" something you don't like off-idle.  You can spend a LOT of time fooling around with different needles (and all the rest of the adjustable parts) and not find perfection.  Sometimes I think it is better to have a campaign geared to having as few undesirable characteristics as possible instead of requiring perfection across the board!  A lot depends on how you ride.  If you blast around all the time you won't notice that it carburets less well when going slowly and vice versa.  Sometimes it can be quite challenging (impossible?)to get really good performance for both situations, so just fool around with it until you like how it drives the way you usually ride.

Thanks!

I guess my mid range cruisung at the moment is mainly biased by my way too small sprocket (2 teeth less than stock).It was plainly stupid to put that one on,when I roll the throttle at low speed I get nice torque but then the bike just "jumps" back and forth...so I definitely need to undo this (gonna go back 1 teeth less than stock,it worked well on my stock 250 setup).

For now I will stay with my needle setup (R5 setup with Dave F mod, feels really smooth).Question was more about the needle position?How does the needle position change mid range perfomance?

Offline jpmobius

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #244 on: May 25, 2016, 12:43:53 »
There is no trend I am aware of.  I tend to look at it this way:  The top end is controlled by the main jet so that is fixed regardless of needle or position (not absolutely, but in general) and the bottom is controlled by the pilot (again, not absolutely, but mostly, in general and for discussion).  The taper of the needle is fixed (which is why considering other needles is often needed)so lifting it higher in the slide makes the mixture richer across all throttle openings within its operating range.  Likewise lowering the needle will lean out the mixture.  So let's say you raised the needle one clip position and now the 3/4 throttle mixture is much better, but now the 1/4 - 1/2 throttle is too rich.  That will tell you you want another needle that has a more gradual taper so it will be larger diameter at smaller throttle openings than the one you are using but have the same diameter at the wider openings.  This sounds simple enough, but unfortunately the carburetor delivers different mixtures depending on the engine rpm and throttle opening.  To understand how this impacts the practical world, consider going WOT at say 4000 rpm.  You will be running exclusively (sort of) on the main jet, but snapping the throttles open at 4k will result in very low airspeed through the venturi, and fuel delivery will be much less than at 10k when the engine is using much more air.  With large venturis,  air speed may fall so low that fuel delivery slows enough to stop the engine.  Similarly, when you snap the throttle closed at high rpm the airspeed is comparatively great and over fueling is the result - though often without much consequence.  Lesser versions of this same situation are continuously happening as you ride and you naturally adjust the throttle for smooth performance.  So in reality, you have a very hard time getting close to perfect jetting under any condition except constant rpm and constant matching throttle opening.  Any time you either open or close the throttle the jetting needs will be different than what is needed once steady state is achieved at the new throttle opening.  That is why digitally controlled fuel injection systems work so well.  You can factor in the current air volume, engine rpm and especially important the rate at which you are moving the throttle and construct a formula to deliver the correct amount of fuel for those conditions.  So with our simple carburetors, we just have to experiment to get the best drivability.
« Last Edit: May 25, 2016, 12:45:44 by jpmobius »
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0

Offline der_nanno

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #245 on: Jun 14, 2016, 02:55:44 »
Hey guys!whats the right way to anneal my copper gaskets:
I used to use a blow torch on them on a flat surface until they discolor.should i wait till they cool down or throw them into cold water?

Dip them in water and repeat once more. This way you also remove all the old carbon on it and the second time is for uniformly annealing the copper headgasket. (Not this critical with a small ring like this, but think of the huge Z1000 headgasket...)

Hey guys!

Long story short:

I canŽt get my right cylinder to seal right.Had along rideout last weekend,oil is slighlty dripping out of the right head when I push the bike hard, so i guess there are a few possibilites now:

.)Go O-Ring on the heads (more machine work)
.)cut out the "right" headgaskets out of 0.8MM and 1MM copper sheet, so that finally the tinkering with the squish mod is coming into play,the stock gaskets has 1.35MM so I wanŽt really using the squish we had planned yet.

I will try this in this order:
->New Headgaskets out of 0.8 and 1MM and if this fails IŽll probably have to go O-Ring

Or simply ask your tame engineering monkey, whether he has run into those issues?  ;D

He'd show you a picture of gascacinch and tell you, that together with the correct torque, it's the dog's danglies.

Oh and based on my notes, you want 0.65 and 0.75mm headgaskets.

... and port work. We all want port work on our two-strokes, don't we.

Cheers,
Greg
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Offline TranceMachineVienna

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #246 on: Jun 24, 2016, 11:00:04 »
So guys!

thanks again for chiming in!

I have a question on a different kind of mattter:my clutch is awful hard to pull, and iŽm definitely not a sissy (had a ducati before the RD and it felt smoother).

I have a new clutch cable, a new Domino clutch lever (the stock one was wobbling around already), everything is nicely lubed and I still have the feeling that i need to squeeze the ish out of this clutch.
is this normal with these clutches?
is it possible that my clutch springs are too hard?

Offline der_nanno

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #247 on: Jul 03, 2016, 05:11:46 »
Hello!

Well, having ridden your bike, I do admit that your clutch is a bit on the stiff side. Normally I'd say stuff like have you oiled the new cable, etc. But in your case, I am inclined to suspect that probably the push-lever assembly needs a bit of cleaning and maybe some dressing up of the teeth and a good bit of lube. If that doesn't cut it, I'd take the clutch pushrod out and inspect the hardened ends for wear. It didn't feel like strong springs to be honest, more like a scratchy lever the last time you've let me drive it.

Cheers,
Greg
Real freedom starts with the freedom of thought.

My Blog:
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My Mule TR1.1 build here on DTT:
http://www.dotheton.com/forum/index.php?topic=75458.0

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Offline datadavid

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #248 on: Jul 04, 2016, 07:16:14 »
No, it should be a light pull with stock springs. I put in some harder springs in mine and its still not very stiff.

Offline jpmobius

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Re: Yam RD "Blue Dream"- Ride,Maintain,Tune
« Reply #249 on: Jul 04, 2016, 10:38:09 »
There are a couple of possibilities.  I'd offer the opinion that RD's have a pretty medium to easy pull - whatever that means - stock and in good order.  If the clutch springs are stock and the clutch itself is ok, obviously the trouble would be in the actuating mechanism somewhere.  Cable routing and length are a common problem.  If the bars have changed, usually the cable need to as well, and often the routing needs to follow a different path than stock.  One way to check it is to remove the tank and all cable interferences and try the cable operation as loose and with as large radius curves as possible to see if the pull is better.  If it is noticeable than that is at least part of the problem.  I think cable routing and length is a lot trickier to get right than most people seem to think it is.  If the throw out mechanism is damaged or worn its operation can be affected.  I'll assume you have everything lubricated already.  Not much can happen with the push rod as long as it isn't bent.  Since you changed the lever, compare it to the stock one.  A very small change here can make a big difference.  The length, and angle of the lever and the distance from the pivot to the cable purchase have a big impact on the leverage ratio and ergonomics.  It is entirely possible to keep the same leverage but have a seemingly stiffer pull just because of the angle between the grip and lever.

It is pretty easy to have non stock springs in a used bike.  RD's don't need a stronger clutch until you noticeably increase the output, but that doesn't stop people from thinking they need one if they are hard on it, ans RD's are famous for having a hard life!  Round up some stock springs if all else fails - I wouldn't hesitate to check out used ones.
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0