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Old 10-26-2011, 03:52 PM   #16
techforlife
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This is getting interesting,,,,,,i actually can stay awake and away from beer reading this...





B
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Old 10-27-2011, 04:11 AM   #17
cyclewizard
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Quote:
Originally Posted by willys View Post
I'm in....I'm at my limit now for information on what next to do to my KLR685 StageII head,ported and polished from airbox to exhaust, bigger valves, Mega Camed, Flatslid, modded exhaust powerplant!!!
I need to know now about how to add compression to a KLR engine with a non adjustable cam timing system! augh!

Subscribed....please advise.....sitting on the edge of my seat!...
I had it 3/4 written out an hit the back button and it all disappeared,,,,,,,,,gawd that pisses me off when I do that.

I'm going to start over..after I get back from Tim Hortons
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Old 10-27-2011, 05:23 AM   #18
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Quote:
Originally Posted by cam14 View Post
Real interested in the finer points of rod ratios. In the context of building a reliable motor, is it really worth the effort to add a long rod and move the wrist pin up to generate a long rod motor. At what point is the rod ratio too short? Since a long rod motor will have more dwell time at TDC, how dose that affect cam timing and demands on lift and duration?

TIA
Cam timing and lift is a good question. I have never heard anyone give this advice,
and I dreamed it up myself. Actually, I figured it out using simple
geometry equations. Any valve lift past 0.25 of the valve head diameter
is basically a waste of time (or lift, more accurately). So, a 2" valve
needs no more than 0.500" of lift. A 1.6" valve head (like an exhaust
valve) needs no more than 0.400" of lift. Flowbench results clearly
demonstrate this when you pay attention to it. Yeah, maybe flow goes up
a bit past this 0.25/1 lift/valve head dia. ratio, but not much compared
with what it does at lesser lifts. I have done flowbench testing where the
flow actually drops off much past the 0.25 ratio point, although that's
a bit unusual. Yeah, most cams you buy have the same exhaust lift as
intake lift and same duration #'s despite the fact on the exhaust side that it doesn't help;
it's just convenient for the machinist to do it this way. Cam duration
(all other things equal) will be affected by the rod length/stroke
ratio. More stroke (for a given deck height) results in a smaller
rod/stoke ratio and that needs a bit more cam duration ... to get the
same timing for piston position (which is what you are trying to get the
valves to open and close for). I've writen articles where a long rod
engine and a short rod engine (otherwise as identical as possible) were
both run on the dyno and the long rod engine gets more horespower with
the same cam. The assumption here is that cam timing is cam timing is
cam timing. But this ignores where the piston is and where the piston is
with a short rod isn't where it is with a long rod at the same crank
angle (like halfway between TDC and BDC for example). So the piston
position with the short rod is NOT the same as it is for a long rod and
THEREFORE with an identical cam the VALVE opening does not occur at the
same piston displacement with different rod ratios. From a piston
displacement viewpoint, a long rod engine gets more cam duration (with
the identical cam setup) than the short rod engine and therefore gets
more horespower ... in addition to lower piston drag which also helps
the longer rod ratio engines. If you get the same valve opening for
piston displacement, the short rod engine needs a bit more cam duration
to accomplish the same actual piston displacement timing. OK, I need a
blackboard to really explain this. The easier thing to do once you get
your bore, stroke determined, and head flowed, is give these numbers to
me C-dub when you want to do your cam, and I will crunch the numbers for you and give you the grind that fits your engines needs. plug plug.......the mods here will probably put me on probation again..


On a big 780XR motor with a ported head I've found it breathes the best at or near 480 lift but not enough to warrant the wear and tear on the valve train, 405 lift seems to be the best all around #'s on big stroker motored XR's for longtivity and power, but if you guys want a cam that large no problem I will do it for you.
The intake valves will come in contact at those lift numbers because of the canted valve design so there are things that have to be done to the head to accommodate these issues.

For smaller displacement 644's to 675 XR's 370/380 lift is plenty..you don't want to over cam your motor. The larger bore and stroke motors can take much more cam than a smaller bore and stroke, the larger bore will mellow the cam compared to a smaller displacement engine with equal cam events.

Now if you want a "large" cam on a smaller 644cc 675 XR than you need to up the comp in the 12 to 13 C.R. range to get it's full effect.
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Old 10-27-2011, 05:42 AM   #19
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Now how do i get all the people i've argued with about 4 strokes to read this Wiz ,that's the kicker.
The long/short rod thing is called dwell angle and yes the fugs can read that too.
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Old 10-27-2011, 05:50 AM   #20
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Another myth I would like to put to rest is the oiling problem people discuss here and over at TT or so they think there's an oiling problem..there's not..it's all in the hands of the opperator.

The only reason" well one of them" people fry there valve train on these motors is they set there idle to damn low, the pump on an XR does not pump enough fluid at low RPM's sitting in traffic........ set your idle to 1500 rpm or more..

If your sitting in traffic on a hot day idling bring your rpm's up to 2000 so the oil can flow and help cool the bike.
When I build a motor or bike for a customer there's a reason why I have the idle set high so don't fricken play with it please... it gives me bad feed back and won't cool properly and you could ruin your new motor...puff it starts to smoke...


Clean your down tube and engine screens and when you pull your side cover off on the clutch side make sure the O-ring and dowel is in place when you put it back on.

One more very important factor here is you have to use a ZDDP additive on these motors or an oil like redline that has a high percentage of ZDDP mixed in the additive package, one other thing is STP has a high content of ZDDP in it also, mix some in there if Redline is not available in your area and Joe Gibbs oil for breakin......
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Old 10-27-2011, 05:55 AM   #21
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Quote:
Originally Posted by Frapper View Post
Now how do i get all the people i've argued with about 4 strokes to read this Wiz ,that's the kicker.
The long/short rod thing is called dwell angle and yes the fugs can read that too.

I've tried many of times myself and I gave up....I usualy just listen and not say much but Mike started a post here that people need to read so this is my .02
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Old 10-27-2011, 05:55 AM   #22
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Dang Paw a dun lernt sumpin new 'agin....

Im redee 4 mohr skoolin
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Old 10-27-2011, 05:59 AM   #23
cyclewizard
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Originally Posted by Wattner View Post
Dang Paw a dun lernt sumpin new 'agin....

Im redee 4 mohr skoolin
Good morning son..
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Old 10-27-2011, 06:00 AM   #24
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Off to Tim Hortons for another cup of joe.. life is good..
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Old 10-27-2011, 06:11 AM   #25
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Originally Posted by cyclewizard View Post
Off to Tim Hortons for another cup of joe.. life is good..
Watch the Joe.... You'll be buzzing' like a 5 dollar pawn shop amp
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Old 10-27-2011, 07:00 AM   #26
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This is all good info. This is what I would assume would be the equivalent to using the degree wheel on a car engine to degree the cam. I always knew it was important just never knew the significance. Listening more closely now.
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Old 10-27-2011, 07:56 AM   #27
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Originally Posted by Krazyjohnny View Post
This is all good info. This is what I would assume would be the equivalent to using the degree wheel on a car engine to degree the cam. I always knew it was important just never knew the significance. Listening more closely now.
I degree all my cams in, on the RFVC motor it's a real pain and nobody wants to do it because the angle of the spark plug hole.

You have to make a special piston stop tool because the angle is sharp and the stopper that comes with most wheel kits is to short.
The piston stopper, on an RFVC head will actualy hit the side wall of the cylinder on the smaller bore 100/102 pistons and makes it hard to stop at TDC, even with the 106mm piston you need to make a new stop.

So I start will a special built stopper to get it close and then I switch over to a dial indicater like you would use to set timing on the older two strokes.

The problem with the cam grinders that sell RFVC cams is "they don't mock" up an engine an degree in there cams, so it's a lot of guess work on there part in which they could be way far retaded or advanced.

To set the cam timing you can slot your bolt holes with a bridgeport mill with the xyz protect feature.
I'm not familiar with the KLR cam gear but I'm sure you could modify it to set cam timing.

If the cam gear has pins you can bore new holes in 2% increments or slot the gears where the pins are, if it has a keyway you can grind a new slot for it..
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Old 10-27-2011, 08:02 AM   #28
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Did you forget about me or did I miss something somewhere?.....augh......which usually happens, me missing the point......augh!

My cams have a .410" lift 250degree at .040"
As said before...KLR685, 1 mm larger valves all round, ported and polishedhead and also the rest of the system to the can from air cleaner, stock base gasket to keep compression stock, same for head gasket, better needle klx needle and 145 main, UNI air cleaner, BigGun header, opened up stock can(soon to be aftermarket) FCR-MX slider 39mm carb.

Now it's possible compression time....can't adjust the cam timing at all easily. the sprockets are single dowel located, it really needs 4 degrees added to it. But that is a very complicated deal by repositioning the dowels to get half a tooths distance or slightly more seeing as each tooth results in 7 degrees of timing.

Please advise....?

Still perched on the edge......
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Old 10-27-2011, 08:15 AM   #29
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That is what I never understood......
This is the most important factor on an RFvc head...squish...Quench, or squish area is typically the flat area on the top of the piston that's almost level with the top of the block deck. It must have a corresponding flat area on the deck surface of the head to qualify as quench.
If you look at a combustion chamber, you will usually see these flat areas, and they will have the volume of the actual combustion chamber between them. When the piston is compressing the mixture, as the piston nears the head, the flat areas on the head and piston come together and force the mixture from those areas to "squish" into the chamber, where the spark plug and burning mixture reside, so you achieve a more complete burn.
The quench area also runs cooler than the rest of the chamber / piston. These lower temperatures are where the "quench" comes from.
When properly designed, the quench areas can have a tremendous effect on the quality of combustion, and allow higher compression ratios, and due to this they are considered "artificial octane" by scientific types.
Bottom line is "properly designed, quench is good".

The old myth that XR's can't run high C.R.'s is just that a myth, if you set your piston and head up right with the .040 to 0.35 deck ht. between the head and piston you'll have less detonation problems than using a 10.5.1 XR600 piston that sits way in the hole.
I mill my heads down to remove the lip and reduce cc's in the chamber, less cc's will give you less spark knock on these motors.
If you want squish pads built into your head to get more artificial octane I can do that to by building a piston with raised pads or by welding new pads into the head, the problem is it comes with a price.

So by just using the age old method of .040 deck clearance will do alot for spark knock and dish your piston to match what C.R. you want leaving an out ring for a squish pad.
The 105/106 piston works good here because it leaves a larger ring for squish/quench.....
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Old 10-27-2011, 08:27 AM   #30
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Quote:
Originally Posted by willys View Post
Did you forget about me or did I miss something somewhere?.....augh......which usually happens, me missing the point......augh!

My cams have a .410" lift 250degree at .040"
As said before...KLR685, 1 mm larger valves all round, ported and polishedhead and also the rest of the system to the can from air cleaner, stock base gasket to keep compression stock, same for head gasket, better needle klx needle and 145 main, UNI air cleaner, BigGun header, opened up stock can(soon to be aftermarket) FCR-MX slider 39mm carb.

Now it's possible compression time....can't adjust the cam timing at all easily. the sprockets are single dowel located, it really needs 4 degrees added to it. But that is a very complicated deal by repositioning the dowels to get half a tooths distance or slightly more seeing as each tooth results in 7 degrees of timing.

Please advise....?


Still perched on the edge......
Sorry, let me address this more accurately...
Have your gears slotted where the dowel pins are located so they will rotate.
You will have to bring them to a shop that has a mill, tell them what you are trying to achieve.
If your gear is held on by a single bolt in the center than have the pin holes drilled a 4degree intervals.
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