lurch
Full Member
Posts: 217
|
Post by lurch on Jul 22, 2007 13:28:16 GMT -5
Hi I've just fitted some R&D valve springs today & have assembled the head complete with new rocker arms ,valves & a high lift fast road cam by Newman here in the UK. I haven't fitted the head on yet but just bolted on the rocker cover & used some 8mm threaded rod through the stud holes .I turned over the cam using the 17mm bolt the secures the cam wheel I'm a little concerned at the force that was required to turn the cam ,I found it quite hard to do & when the rocker went over the top of the cam lobe the valves shut with a almighty thwack I thought the head of the valve was going to snap off !! I was using a socket in a ratchet to turn the cam so the valve would sort of freewheel shut under the presure of the new springs . The R&D spring Kit # VSK110Y are about 10mm longer than the old ones & I have checked all the measurments in the fitting instructions, is the camchain going to be up to the job dont fancy it snapping and the valves hitting my new Wiseco piston ,take a look PS I think Stew Ross is using these springs ? Cheers LURCH  |
|
|
|
Post by StewRoss on Jul 23, 2007 2:47:06 GMT -5
Hi, Yes it takes a bit of force to get these things going doesn't it. I would use a stronger cam chain in any case...as you say it is pretty hard to turn these things over. One thing though, have you set up the springs to the correct installed length...can't recall what they should be right off...have the paperwork around here somewhere. It should have come with the springs. Do some measuring and check it out. Also make sure they can't coil-bind at full lift as well... I'll check up on the stronger grade of cam chain and get back to you. SR  |
|
lurch
Full Member
Posts: 217
|
Post by lurch on Jul 23, 2007 4:10:42 GMT -5
Thanks Stew I have measured the installed hight and its 1.648"well within the 1.625" to 1.670" tolerance , I dont know how to check for "coil bind" as I cant see anything with the rocker cover installed the cam lobe hight is 39.42mm inlet & 39.38 mm exhaust Just as a test I turned the cam over using my torque wrench starting at zero and moving up in 1Nm increments , it went up to 22Nm before the cam would go over full lift , that seems a hell of a lot to me !! but then I've never worked in anything with a cylinder capacity of more than about 250cc usually Multies . just a side note, I have another cam & followers which i bought on ebay ,the followers are a slightly different designe have a raised pad on the part that contacts the cam ,the lobe hight on this cam measures 38.91mm inlet & 38.93mm exhaust thats well below the standard hight that I have in my manual of a minimum of 39.08 mm inlet & 39.10 mm exhaust Phew all these numbers are making me dizzy  Cheers LURCH |
|
|
|
Post by StewRoss on Jul 24, 2007 3:00:09 GMT -5
Heh, heh...have fun with it all. You can check for coil bind at full lift on the cam...if you can't see with a mirror etc...perhaps place a thin feeler gauge between the outer coils and then see if it''s easily removed at full lift...you may need to improvise a little... The cam chain is a DID (DHS) 219FTS...106 links. SR |
|
lurch
Full Member
Posts: 217
|
Post by lurch on Jul 24, 2007 4:48:47 GMT -5
Hi Stew
I have a new camchain, purchased from Kedo in Germany but it reads slightly different ,its a DID (DHA)219FTS(S) 106 links
Would this be the number of the standard chain ?
BTW here's a copy of a email that i recieved from the owner of the company that made the cam , I think its a little to radical for on road use so I'll probably sell it on & look for another less wild cam better suited to my needs
Cheer's
LURCH
Her's what David Newman of Newman cams wrote
Hello Jim
The cam has .320 Cam Lift and the duration I do not know at the present time as the records are on an old PC System
Which is now defunct?
The material is EN40 B Nitrided steel so use the latest hardened followers.
This is a cam that we manufactured for BHIR Racing on the French/Swiss Border so you may be able to get the timing from his website it is the highest stage of performance offered by them for this engine.
If the engine runs OK with the Standard springs us these, try to keep away from heavy poundage springs.
Regards
David Newman
|
|
|
|
Post by christoph on Jul 28, 2007 19:35:34 GMT -5
why is this?
|
|
|
|
Post by fenz on Jul 30, 2007 21:07:58 GMT -5
.320" cam lift is not very much most of the hot cams i have been looking at are around 0.455 to 0.465.
|
|
|
|
Post by colinjay on Jul 30, 2007 22:31:35 GMT -5
Christoph,
Re your "Why is this?" regarding running the STD valve springs with a modified cam if you can.
The theory goes something like this.
If you increase the strength of the valve springs (i.e. use heavy duty springs) they with make the the cam followers (rocker arms) follow the cam correctly and not move away from the cam as it reaches maximum lift. As very hot /wild cam can, at high engine rpm, accelerate the follower (rocker arm) and valve so quickly that as the cam reaches maximum lift the momentum of the valve keeps the valve moving and you get what is called valve bounce of valve float. So for this reason, heavy/strong valve springs are good because your valves open and close under full control of the cam, and hopefully the bike goes as well as the cam designer said it would!
However, like everthing in life, the strength of the valve springs has to be a compromise. The biggest problem with strong valve springs is the amount of load that they place on the follower to cam interface, i.e. the area where the cam and follower (rocker arm) meet. If the springs are to strong, it can result in a breakdown the oil film/layer that is between the surfaces of the cam and follower, resulting in wear to both the cam and follower. This wear, to a point, can be overcome by using hi grade/quality (synthetic) oils that have a very high film strength, but this is only masking the real problem of the valve springs being to strong for the cam and follower design. This type of wear/lubrication problem is more apparent in air cooled engines and is probably one of the reasons that Yamaha modified the rocker arms on the later model SR's. Most people who have worked on SR/XT/TT engines for a while have seen at least one a top end destroyed by over heating/lubrication failure in the cam/rocker arms area.
SO, to get to the STD valve springs. If you have a modified cam in your engine and you don't have problems with valve bounce/float at high rpm then the valve springs are doing their job properly. Conversly, even if you do get some valve bounce/float at very high rpm, if you don't rev your engine to the red line every time you ride, them the STD valve springs will not be a real problem and you will not be placing undue stress on the oil film between the cam and rocker arms.
To go further on the topic, there is a school of thought amougst some engine tuners, notable Dave Degan in the UK (this is the guy who built the Dresda Triumph Tritons in the 60's along with a lot of other racing Triumph twins and is one of the gods of 1960/70's tuning), that actually fit lighter than STD valve springs. The theory being that by designing the cam correctly AND lightening the rocker arms etc, and using very light weight (titanium) valves with thin stems, you don't need a heavy/strong valve spring to keep everthing under control. You also have less stress placed on the oil which results in lesswear etc.
I could go on further, but my lunch time is over and I better get back to work.
CJ
|
|
|
|
Post by canucksr on Jul 30, 2007 22:54:15 GMT -5
I've heard of the "Lighter valve spring" theory before. I think the reason they work well is that the wire is oval, instead of round, and the spring itself is shaped like a cone...tapered at the top. Anyway Cj, that was an excellent tutorial during your lunch.
|
|
|
|
Post by frankyb on Jul 31, 2007 3:01:51 GMT -5
Hi guys, if you think that heavier valve springs may be to strong, and the standard ones may be to light, then split the difference and put an extra valve spring seat washer under the standard spring and try it. It wont change the spring rate, but it will preload it slightly, enough to give the effect of a slightly heavier spring. Cheers Franky b.
|
|
|
|
Post by colinjay on Aug 6, 2007 17:34:27 GMT -5
Hi guys, I was looking for something totally different in the shed on the weekend and came across these two items from the past, which have a passing relevance to the topic of valve springs.  The piston on the right, is a Hi comp piston from a SR500 that dropped a valve. The engine was fitted with a very wild cam and a set of S&W HD valve springs. The head broke off of the valve and trashed the engine. I actually had the cylinder head repaired (it had a good/expensive flow job), but it took a lot of welding and grinding plus having to have a new inlet valve seat fitted. The piston on the left I took out of a late 70's Ducati 900SS when I worked as a mechanic in the early 80's. The rider (not the owner) had fallen off of the bike and the throttle jammed wide open. Proof that even desmodromic valve gear can't save your engine when it is really over rev'd. CJ |
|
|
|
Post by wotavidone on Aug 6, 2007 19:04:07 GMT -5
Colin,
I like your thinking on valve springs. Have seen worn/stuffed cams, broken off valve heads, you name it.
One thing we always look at in the car hot-up area is what the cam is ground for.
The trick, according to the build up article in VMX magazine is to get a new cam rather than a regrind, as this ensures you have a full size base circle on the cam, whereas regrind cams require you to remove metal from the base circle if you are looking to get more lift.
My mechanic mate reckons the end result of a regrind like that is that you end up with the ramp up and down from the cam lobe too steep/sudden, and this contributes to chattering as the cam follower tries to follow the cam. The "cure" for this is to run heavier springs to force the cam follower to stay on the cam properly, with the resultant wear/reliability issues you have touched on.
There is a certain very well-known brand of cam he won't touch due to they always seem to have premature lobe wear, and he reckons too steep ramp- up is the culprit.
So you need to pick a cam, with a full size base circle, that the cam manufacturer recommends a reasonable sort of seat pressure, higher than standard maybe, but not insanely high.
I'm not sure I understand anyone wanting to get an SR engine to rev higher. To me it's all about the mid range and bottom end grunt.
And the one thing about cams ground for low to mid range grunt is they won't have ridiculous lift, so the springs don't have to be ridiculously heavy either.
Getting back to the photo of the springs, I reckon the new ones will not bind. They may be longer, but they have less turns and the wire is thinner. They'll be fine I reckon.
Mick
|
|
|
|
Post by StewRoss on Aug 7, 2007 2:47:23 GMT -5
I have a piston like the one on the left but with a lot more crown missing...a big hole...the exhaust valve broke off and forced its way through! It was a Wiseco 88.5mm HC one. SR |
|
