Yam RD "Blue Dream"- Ride,Maintain,Tune

ha i say if you practice you should be able to get it up on a wheelie in 2nd and gearchange thru 5 on one wheel ;D
srsly though being able to upgrade over the winter to a 350 is like cheating !!
not a lot of bikes you can do that with
as far as the combustion chamber sure it would be a good idea to check basic volume now, record the number, but if someone has machined the dome or squish,then you need to check the profile and squish clearance on your assembled engine..with the pistons you will run,clay solder or wax i like the solder, some of the very fine solder, 4 strands twisted like rope and they squish easy
whatever you decide you want should be exactly the same on both
too much fun !!

Haha xb this is exactly what i am looking for....was kinda hard till now with the 250 pulling off wheelies (1st gear and a loooot of clutch ).
Could you elaborate more on the solder method?
How do i exactly measure then the distance to the piston tdc?

Thanks man!!

Ryan Stecken said:

Haha xb this is exactly what i am looking for....was kinda hard till now with the 250 pulling off wheelies (1st gear and a loooot of clutch ).
Could you elaborate more on the solder method?
How do i exactly measure then the distance to the piston tdc?

Thanks man!!

Click to expand...

just google 2 stroke squish then click images
lots of ways to measure it but the large solder can be taking a lot of force rolling thru tdc to form it
3-4 strands of fine small solder just twisted together like rope takes much less force to form in the squish
the idea is very simple , make a model,pattern of an area dimension,that otherwise would be tricky to measure
to make sure the squish is even putting the solder at 4 places hold it to ther piston with grease

Or just nick some modelling clay or cookie dough, whatever you have in the house. 8)

Cheers,
Greg

der_nanno said:

Or just nick some modelling clay or cookie dough, whatever you have in the house. 8)

Cheers,
Greg

Click to expand...

If this use corn starch as a release

ive tried clay and wax they are hard to pick and too soft to handle a measure .;.
the twistedsolder makes the process more gooder,easy wise you can pick it up and ram the caliper jaws shut on it it dont dent like klay it foolproof thats ,thats all

Yup.

Yep, solder to measure the squish clearance. Your modified heads (those are either very early RD or R5) look to have way overly wide squish bands. RDs have exceptionally sloppy fit being located by the head bolts only. You will need to fix that if you are going to bring the squish clearance to a desirable figure (.038"). The sloppy fit makes it possible and likely that the head will not be centered over the bore and the squish will be too small on one side and too large on the other due to the slight dome of the piston and taper of the squish. The best thing to do is to machine the head so it has a flange that sits down inside the gasket recess on the cylinder. This will exactly center the head on the bore and keep the squish clearance uniform all the way around the cylinder. You can also solve the head sealing problems by machining a groove for an o-ring at the same time. Once you have heads that seal and align properly you can cut the squish for proper clearance. Check it with the solder at four points (12, 3, 6, and 9 o-clock) to be sure you have uniform clearance. Then you can cut the combustion chambers for an appropriate volume for the fuel you will be using.

jpmobius said:

Yep, solder to measure the squish clearance. Your modified heads (those are either very early RD or R5) look to have way overly wide squish bands. RDs have exceptionally sloppy fit being located by the head bolts only. You will need to fix that if you are going to bring the squish clearance to a desirable figure (.038"). The sloppy fit makes it possible and likely that the head will not be centered over the bore and the squish will be too small on one side and too large on the other due to the slight dome of the piston and taper of the squish. The best thing to do is to machine the head so it has a flange that sits down inside the gasket recess on the cylinder. This will exactly center the head on the bore and keep the squish clearance uniform all the way around the cylinder. You can also solve the head sealing problems by machining a groove for an o-ring at the same time. Once you have heads that seal and align properly you can cut the squish for proper clearance. Check it with the solder at four points (12, 3, 6, and 9 o-clock) to be sure you have uniform clearance. Then you can cut the combustion chambers for an appropriate volume for the fuel you will be using.

Click to expand...

thank you guys for helping me out!

so if i understand correctly i cannot use these heads for my 350 barrels since the domes are too wide,or is possible to bring them back to a smaller diameter?

Anything is possible, you can weld them closed entirely and re cut them to your specs.

Likely you will have to do nothing different than what you would do to stock heads. Anyone familiar with this sort of work should easily be able to alter the ones you have correctly. The first thing to do is bolt them on and determine the squish clearance you have now. That will tell you where the mating surface to the cylinder needs to be and that surface can then be machined accordingly as can whatever angle you want the squish band to be. I match the crown of the piston, but I believe slightly more angle is used by many. If you are going the o-ring route you will not have to account for the gasket. If you wish to keep using the gasket, I suggest you also machine the tops of the cylinders so you can use RD400 gaskets. You will have a nearly impossible time getting the stock 350 gaskets to seal, which are a problem on a stock bike if it runs well. The heads you have are the least desirable as they are the least stiff, and you will be making them thinner with the modifications making this issue even worse. The best plan is to keep the head as thick as possible, machine a step in it to fit the gasket recess in the stock cylinder and cut a groove for an o-ring. All the issues will be solved and the heads you have should be just fine and seal with no problem. 350 cylinders are actually better to work with in this regard as they have the step to locate the gasket and you can use that to center the heads. 400 cylinders are flat on top and require pins to locate the head which is a pain to do. Altering the heads is one of the best mods you can do for an RD. My totally stock (points and everything!) '74 model has this done as its ONLY modification and it is very fast (for a stocker!)and super reliable.

hey mobiuos maybe some more big words for me ? i am ruunning low on big words
just be sure they arent made up ones ok ?
and as always the information you provide rivals that of kevin cameron
i had thought about suggesting 2 dowl pin type locators but there doesn't seem to be a good place for them and they would fiddly and a pain to deal with
my other thought,just to throw out ideas,would be using a pair of the head bolts across corners as dowels by turning them down slightly and shrinking on a short sleeve that would rest at the joint
that may also require match reaming the holes but no matter the step is the proven winner
carry on

Make sure your base gasket is stock or stock height, check port timing then squishy squishy... then you can adjust things topside or bottomside, but if changing deck height re check port time...

To center the head you can cut a wood plug the size of the bore or close and wrap with even layers of tape to make snug, drill a dowel hole init the center the size of a spark plug and and glue a dowel init, slide the head onto the dowel, slide the wood plug into the cylinder and use the two alignment holes: in the 400 gasket to mark the top of the cylinder, take it all apart drill two 1/8" or whatever holes just deep enough to use two alens to align the head

yeah good work minds alike, i have acually done it with a i cant remenber quite but similar rube goldberg methodology on a couple off road racers back in the day
and as long as it within 10 thou of perfect is a good job

Machinists think in thousandths mechanics think in hundredths... tomatoes and catsup

Ryan Stecken said:

thank you guys for helping me out!

so if i understand correctly i cannot use these heads for my 350 barrels since the domes are too wide,or is possible to bring them back to a smaller diameter?

Click to expand...

It's pretty much what I told you, when you showed me the heads the very first time at your dad's shop. That said, I could surely weld them up for you and then re-machine them. But in all honesty: Let's first build the engine, check the actualy squish, come up with a PROPER way of sealing the bl**dy lot and then we take it from there. That said, you still have the 250 lids, which AFAIK should be unmolested, which in the same turn means, we can put them on my lathe and shape the combustion chamber the way we want 'em to.

Cheers,
Greg

I was going to suggest that as well - your 250 heads should also work fine as a base for making the new ones. Maybe I'm not seeing it in your pics, but it does not look like you will need to weld anything up on the 350 heads. Certainly you would want to machine them to fit the cylinders and get the squish clearance first and then see where your volume is at. If too big at that point then obviously you would have to add material, but I'm betting that by the time you get it to that point you will be taking more material out to get the compression down to pump gas level.

Yeah, they are a bit tricky to pin. I turn a piece of aluminum plate to fit the bore very closely, and bolt it into a little fixture that threads into the spark plug hole. Not as accurate as it might sound - there are a few components and precision is lost but plenty good enough to be a lot better centering the head than the sloppy head bolts! I just drill between the fins near two of the head bolt holes with the heads bolted to the cylinders and then put in a couple of split/spring/tension pins for dowels. Never thought about shimming the head bolts - you could get a nice tight fit (maybe have disassembly issues if corrosion gets in there (Suzuki 750!)) but probably not have the head centered - just repeatable off center. If you could figure a way to machine the head off the bore center it would work great though!

Well if you have a lath then get an old over bore piston and cut it for a centering tool... with a little motor honey you will have a hydraulic effect auto centering it gnats ass.

I don't know how we ever ripped these apart as kids and made em run again... will this RD be heading to Mars soon?

Tune-A-Fish said:

Well if you have a lath then get an old over bore piston and cut it for a centering tool... with a little motor honey you will have a hydraulic effect auto centering it gnats ass.

Click to expand...

Never thought of that with the motor honey - genius!

good points to consider i hadnt thought about that but we use the threads for turning in the lathe so unless the stud hole areconcentric to the plug hole my method has an ishoe but you know what i would bet that that is a tolerance that was always held those oversize holes being on a concentric layout it could easily be seen when spinning in the lathe
mobius you would hear it as the lathe tool hit the holes if they were uneven it would sound like a harley !!!! hahahahahahahaaha