[Don3rd]

Hello everyone, new member here, first post!

I tore into my 2005 brute today for a top end rebuild. I bought it with around 2k miles (I don't remember exactly) and now it has around 2600.

To start with symptoms: It has always ran OK but felt like it didn't have all the power that a brute force 750 should. Always smoked a little, exhaust smelled kinda funky, and goes through oil. So, I figured a top end rebuild was due (pistons, rings, gaskets, valve seals, whatever else).

I checked compression and both cylinders were at 56 psi (spot on) but I thought that was a false positive due to carbon deposit buildup helping the compression. So, I turn the motor to TDC rear (the TR on the crank rotor was lined up in the timing inspection hole) and pull off the rocker cover. Come to find out, the rear camshaft appeared to be 180 out. The timing marks on the camshaft were lined up with the head surface, but the arrow was pointing down instead of up. The front camshaft was lined up properly with the arrow pointing up. I took out the cams and pulled the heads. The pistons and cylinders look great - no scoring or scratching AT ALL. This is my first rebuild but in my opinion I would say they look damn near new.

Is it possible that the previous owner did a top end rebuild and the rear camshaft was installed 180 out?

Or is it possible that the arrow was put on the wrong side?

I am confused because I would think the motor would hardly run well at all (and possibly bend the valves?) but I've had it up over 50mph.

For reference, when the piston was TDC, the cam lobes were pointing up which I think would be wrong? That explains why there was no clearance between rockers and valves when I checked valve lash. I just thought it had never been done before. I want to make sure I have it right when I put it all back together.

Sorry to rant, just trying to give as much info as possible. Let me know what you guys think!! Thanks!

 

[dman66]

Did you watch the rear head exhaust valves open then close, then watch the intake valves open then close, then go another roughly 3/4 of a turn on the engine, then check the cam position ? Looks like you are on the wrong stroke - the piston is down in your pic.

Here's a link for when we check valve clearances :

https://www.google.com/url?sa=t&rct...ScjXlbCFyj7TPvkbhycT_w&bvm=bv.131783435,d.dmo

 

[NovaKaw650]

Since you've torn it apart now (I'm assuming you've removed the cams), there's no way to know if it was out 180 degrees. It could have been dead on.
The crankshaft makes two turns for every one turn of the camshaft. The TR mark goes by the window twice for every one rotation of the cam. So it could have been right on.
The only way to know if it's out 180 (other than the sound and lack of power) is to compare the TDC/top of the power stroke of each cylinder. They should be .75 and 1.25 of a crankshaft rotation apart. If one cam is out 180, the two cylinders will fire .25 and 1.75 of a turn apart. A quick babang, and then a long gap before the cylinders fire again.
As far as the arrow goes, I don't remember ever seeing an arrow on the cam sprocket.

 

[NovaKaw650]

It also looks like it's time to search for my valve adjustment method again.

 

[dman66]

The intake valves are known to get out of spec as to where they can start to pull up through the head, so checking valve clearances is a must. If you install new intake valves and valve seals, you wont have to check them as often. Where both spark plugs fouled with a lot of carbon or just one of them ? If you did not disturb the piston jugs, you should be able to re torque the heads back down good. The piston and cylinder look good to me. Check the cam lobes for wear score marks.

 

[NovaKaw650]

While the following is specific to valve adjusting, it gives an explanation of the engine cycles.

The simplest, most surefire method to adjust the valves and NOT do it on the wrong cycle:

Pick a cylinder. Remove the adjustment access covers. Rotate the crank in the normal direction of rotation and watch what the valves are doing; watch for the exhaust valves to open and then close, then the intake valves will open and then close. Once the intake valves have closed, start watching the flywheel for the TF or TR (depending on what cylinder you are doing) mark to come around to the viewing port (about 1/2 turn of the crank). Adjust all the valves on that cylinder.
Now do the same process for the other cylinder.
Done.

 

[kickstart]

I've been researching and digging into this a lot the last week or so lol, and from what I gather, if the timing arrow is down instead of up, the cam is 180 degrees from correct, and it should run like crap.

If the cams are installed properly, the rear lobes should be flat (or down in other words) across the shaft when the TR mark is in the window, and front lobes should be flat (or down) when the TF mark is in the window. You don't really even need the arrow mark to look at if you understand this (that's why the aftermarket cams don't have an arrow), but you can probably see that the arrow points to the flat, or down position on the lobes. If it doesn't, the flyweights/sprocket on the end of the shaft have been installed wrong.

I've also learned that when setting cam timing, the crank is supposed to be turned clockwise as opposed to being turned counterclockwise for adjusting the valves.

Kawie's training video on timing cams.
https://youtu.be/cBJicCPBC8M

Another good one:
https://youtu.be/mKGpQu8NJiI

 

[kickstart]

Another good video of it:

https://youtu.be/oZEVdiq00BQ

 

[kickstart]

This video shows valve adjusting just like how Novakaw650 describes. It also shows what the cams look like when timed right:

https://youtu.be/wmlQ52zZokU

 

[NovaKaw650]

I've been researching and digging into this a lot the last week or so lol, and from what I gather, if the timing arrow is down instead of up, the cam is 180 degrees from correct, and it should run like crap.

I just realized why I never noticed the arrow,; all I ever look at is the cam lobe position, lol.

Re-read my first post above.
Don't get caught up on whether or not the arrow (and the lobes) are up or down at this point. If Don3rd had rotated the crankshaft one more turn when he first looked at it, it would have appeared fine.
What matters as far as the cam position/timing, is where the cam timing is in relation to the other cylinder.

 

[Don3rd]

Ok, I guess it's possible that I was 180 out on the crank... I thought TR meant you were TDC on the rear piston, I overlooked that the crank rotated twice for every 1 rotation of the cams. (I am a beginner with this stuff)

Luckily I paintmarked my chain and sprocket in the position it was in just to be safe before I pulled everything apart. The picture of the piston was actually the front cylinder. When I pulled the head off the rear cylinder the piston was at TDC.

Reading back through the service manual, I did the rear rocker case first where it only says to rotate the crank 270 and stop at TR. What I missed is that it tells you to do the front rocker case first and the manual says to turn the crank until you hit TF AND the cam lobes are pointing down (ensuring that you are on the compression stroke).

That's a big time small mistake on my part, thanks for helping me realize that! Appreciate the feedback guys!

Any other pointers for what I'm working on is appreciated too!

 

[Don3rd]

Update: In talking with my coworkers, I still haven't found a smoking gun on the oil burning. So since I'm in it this far I'm going to check the jugs for cross-hatching. I'm told cross-hatching is good? Then I will probably pull the jugs and see if the rings are in spec, even though compression was good. My buddy had good compression in his raptor but then checked his rings and they were junk, so I think it's worth a check since I'm this far in it anyway.

 

[NovaKaw650]

The cylinders are nikasil coated and hard as a rock, so I don't know how much marking you will see.
That being said, if an engine is burning oil, and you can see a bold cross-hatch pattern on steel lined cylinders that have enough running time to be broken in, then the rings haven't seated, and it needs to be honed again and a new set of rings installed.
The cross-hatch marks should be nearly gone once broken in.

 

[Don3rd]

You clearly know a lot more about it than I do. Just checked my jugs, and I don't see any cross-hatching or scoring whatsoever. Is that a good sign? Also checked my diameter at the top of the cylinder and this is what I got:

Rear cylinder front to back 3.345in
Rear cylinder side to side 3.345in
Front cylinder front to back 3.345in
Front cylinder side to side 3.346in

My jugs are still installed, so measurements are subject to error but I tried to find the max in each direction and should be pretty damn close.

In your opinion, should I remove jugs and look at pistons? For the small cost I'm thinking it might make sense to just do the rings while I'm here. What do you think?

Also, both cylinders had 56 psi compression before tear down.

 

[Don3rd]

Here's another question for ya... I will be rebuilding the carbs as well. Does that mean I should automatically synchronize them? The manual says you can disassemble without buying a synchronization unless you touch the pilot screw. If I avoid touching the pilot screw do you think I'm safe without synchronizing? It's just another $40-$50 for a vacuum gauge if it's necessary.

 

[NovaKaw650]

At least replace the rings; it's burning oil, it has to be getting in there somehow.
You will need to sync the carbs if you split the two carbs apart. Don't worry about the pilot screws changing the synchronization.
DON'T rebuild the carbs unless you suspect a problem, and then still don't rebuild them. Clean them if there's a problem, otherwise leave them alone.

 

[Don3rd]

Interesting, I just thought a carb rebuild was a good idea while I was in here. Why are you against the rebuild if I have to do some disassembly to clean it anyway? Easy to screw something up?

 

[VTwinKawi]

rebuild implies new parts which you dont need, you can clean the jets if they have some crud in them, the original jets work best

 

[Don3rd]

Great advice. I actually already ordered a rebuild kit ($50 or so) but that doesn't mean I can't return it if there's not really an added benefit.

And for the record, no synchronize necessary since I pulled the carbs off together and never separated them?

Thanks again for all the help.

 

[NovaKaw650]

Great advice. I actually already ordered a rebuild kit ($50 or so) but that doesn't mean I can't return it if there's not really an added benefit.

And for the record, no synchronize necessary since I pulled the carbs off together and never separated them?

Thanks again for all the help.

No synchronization needed.
If you don't suspect a carb problem, then don't mess with a good thing. If anything, do your rebuild first, get it running good, then think about the carbs after. Don't complicate things.