Intake or compression stroke timing?


21 replies to this topic
  • Hart0506

Posted March 19, 2015 - 09:49 AM

#1

I apologize for dragging this topic out again but I have been surfing and couldn't get any real clarification.

So I bought a 08 yz450f and decided to shim the valves this winter. All the valves are in spec and I'm setting the timing. My question is does the engine fire on both compression and intake stroke tdc's? If this were the case it would not matter if while on tdc of intake stroke, I could take the tension off the cam chain. Rotate both cams 180 degrees opposite each other, now making that the compression stroke with the marks lining up with the engine case and 13 pins between 12 o'clock marks. Come someone help me out? Just wanna make sure I don't shag something up by doing so.

Also, I kept tension on exhaust side of the chain while setting exhaust cam, kept the tension between the two cams while setting the intake cam, but when I install the tensioner again the intake cam seems to roll slightly under the edge of the case. Is this normal?

Appreciate everyone's help!
Cheers

  • grayracer513

Posted March 19, 2015 - 10:02 AM

#2

If you know that the 4 stroke requires two full rotations of the crank to complete a cycle, and you know that the ignition is triggered at the crank, you have the answer to your first question.  The engine fires every time around.  Only the camshafts determine which upstroke is compression and which is exhaust, so you cannot make the same mistake as you could if the ignition fired only once in 4 strokes.  It matters not in the least which TDC one uses.

 

To your second question, the timing marks are just marks, and not terribly precisely located, and they will rarely line up just exactly.  The condition you describe does, however call into question whether your timing chain is "stretched"  (actually, the stretching is the result of the cumulative wear in each of the several pivot pins).   It's also worth noting that the engine is extremely easy to rotate in the 6 or so degrees right around TDC, so the best practice is to roll the whole thing back about 10 degrees from TDC, then forward again to align the flywheel marks, then reread the marks on the cams.  The question for you to answer now, it whether it would be closer to lining up if you moved the cam one way or other.  Probably not.



  • Hart0506

Posted March 19, 2015 - 10:21 AM

#3

The guy I bought the bike from replaced the valves cam chain and tensioner before I bought it from him with minimal hours after swapping it so i don't think it's stretched. I tried rolling it back 10 degrees and re reading but same issue. Tried rotating intake cam back a tooth and reapplying the tension but it's way off then. If I line them up directly with the engine case the tdc mark is about 5 degrees off ccw . I tried moving both cams 1 tooth ccw and applying tension again but it seems way more out of whack when I do that

  • Hart0506

Posted March 19, 2015 - 10:32 AM

#4

ImageUploadedByThumper Talk1426789919.178756.jpg

This is what the marks are doin when it's at tdc and tensioner in

  • Hart0506

Posted March 19, 2015 - 10:34 AM

#5

[attachment=229729:ImageUploadedByThumper Talk1426790060.059749.jpg

This picture is a bit better

Attached Thumbnails

  • ImageUploadedByThumper Talk1426790060.059749.jpg


  • Hart0506

Posted March 19, 2015 - 10:36 AM

#6

ImageUploadedByThumper Talk1426790159.145815.jpg

This is what the lobes look like at tdc

  • 03yzf450-kuke

Posted March 19, 2015 - 12:03 PM

#7

Set it up to where the marks are closest to where they should be. Myself I have never seen them line up perfectly even with new chain

  • 03yzf450-kuke

Posted March 19, 2015 - 12:06 PM

#8

From that last picture if motor at tdc I would say you need to bring intake can back one tooth. Exhaust lobes and intake lobes should be a mirrored image at tdc

  • grayracer513

Posted March 19, 2015 - 01:11 PM

#9

Exhaust lobes and intake lobes should be a mirrored image at tdc

 

No, they should not.  The picture here is correct.

 

To the OP: your engine is timed correctly, assuming TDC.  However, you will notice that not only the intake, but both cams are rotated back slightly.  This means one of two things; either the chain is in fact longer than it should be, or you may not be using the correct mark as a reference.  The flywheel will have 3 radial marks on it.  As viewed through the timing port, the first two marks from left to right are usually joined by a horizontal line.  These are for checking ignition timing at idle using a strobe light. The third mark is TDC.

 

lobes_zpsfs9tdgrj.png



  • Hart0506

Posted March 19, 2015 - 01:20 PM

#10

I guess the chain may need replacing. It was running like a top last summer though. Started 1-2 kicks cold and usually 3 kicks when hot. No popping or bogging. I can't get the damn thing to start now. I'm positive the timing and clearances are correct. Brand new air filter. She's getting a strong spark. I thought the float might of been stuck but it's fine. Is there a trick to getting a bike started after having it completely dry? She's topped up on all her fluids. She just won't go... Got the choke pulled and kicked it like 20 times. Not a gig

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  • grayracer513

Posted March 19, 2015 - 01:30 PM

#11

The timing being off that amount will not cause it to be so hard to start.  What frequently does happen, though is that as the fuel in the carb dries out, it will leave a film in the pilot jet metering orifice.  The jet can even appear unobstructed, and can pass air through it, but still be effectively blocked.  The orifice in a #45 pilot, for example is .45 mm.  That's .0177".  If a film of varnish only .001" thick develops in the pilot, that reduces the jet from .017" to .015", the size of a #38.  Running a #38 jet in your bike would make it run pretty much like crap unless you were above 8000 feet, and be very hard to cold start, and the films that form are rarely that thin.

 

Read this: http://www.thumperta...o/#entry6879695



  • Hart0506

Posted March 19, 2015 - 01:36 PM

#12

Thanks. I'll try popping the pilot and main jet out and give them a quick rinse and see if that helps me out. I'll keep ya posted.

  • Hart0506

Posted March 19, 2015 - 02:16 PM

#13

ImageUploadedByThumper Talk1426803211.014731.jpg
Every time I turn the fuel on it immediately starts coming out this drain even though I have this scew turned all the way in. I don't know why? Any input would be great. This is the only reason why I can't start my bike right now. All the fuel is draining right out

  • grayracer513

Posted March 19, 2015 - 02:20 PM

#14

Thanks. I'll try popping the pilot and main jet out and give them a quick rinse and see if that helps me out. I'll keep ya posted.

 

That won't clear a clogged pilot.  Read the link I posted.



  • Hart0506

Posted March 19, 2015 - 02:27 PM

#15

So would I just stick the wire right up through the jet where it is in the carb and confirm it comes through the other side? Not to familiar with carbs just yet. Still learning. Any explanation for that last post I made about the drain? It's closed all the way but the fuel just drains right out of it as soon as I turn it on

  • grayracer513

Posted March 19, 2015 - 02:42 PM

#16

Yes.  The float is stuck.  That, or there is something on the needle seat holding it open.  The drain hose connects to a standpipe in the carb that sits above the normal float level, but lower than the carb's airway. When the level gets higher, it runs down and out.  The drain screw you point to taps into the side of the standpipe passage and opens to the bottom of the bowl if you loosen it.

 

The pilot jet will have several cross holes in it, which should also be free of obstructions, but the main concern is the very small orifice at the small end, where the fuel is actually metered.



  • Hart0506

Posted March 19, 2015 - 02:51 PM

#17

I had the bowl off and the float is moving freely as well as the float needle. The bowl couldn't of filled that quickly. I only opened the fuel cock for a split second and the fuel just goes straight out that overflow I'm gonna pop off that bottom cover and have another look at the float needle. I'm thinking I'm gonna need to haul the carb off and give it a overhaul.

  • Hart0506

Posted March 19, 2015 - 03:25 PM

#18

Yes. The float is stuck. That, or there is something on the needle seat holding it open. The drain hose connects to a standpipe in the carb that sits above the normal float level, but lower than the carb's airway. When the level gets higher, it runs down and out. The drain screw you point to taps into the side of the standpipe passage and opens to the bottom of the bowl if you loosen it.

The pilot jet will have several cross holes in it, which should also be free of obstructions, but the main concern is the very small orifice at the small end, where the fuel is actually metered.


So I found the issue. The bowl is cracked where that drain plug screws in. I guess I was a bit too aggressive last time I opened and closed it again. Can you buy the bowl seperately? Or is there another fix for this. Some kinda sealer/adhesive that's not soluble in gas?

  • grayracer513

Posted March 19, 2015 - 08:37 PM

#19

The bowl's not available from Yamaha, but you should look at Sudco



  • Hart0506

Posted April 15, 2015 - 07:36 AM

#20

So I fixed the crack in the bowl with some jb marine weld for the time being. But the damn thing still won't start. Got the fuel on choke pulled out and I'm twisting the throttle as I'm kicking the thing over but she won't go.. It's getting some fuel because every 4 or 5 kicks it backfires. Does this mean I'm way to lean and should consider bigger main and pilot jets?





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