Starting problems

[gv550]

The decompression device will be activated (1 exhaust valve held partly open in each cylinder) at cranking rpm to reduce the load on the starter, that is the purpose of the device. It will de-activate somewhere above cranking rpm but below idle rpm, likely 500 to 800 rpm. The measure-able compression will be less than if the engine did not have a functional decompression device and the specifications are adjusted accordingly. Holding the throttle wide open would have to be done manually at the butterfly, the twist grip alone doesn’t open the throttle at cranking rpm.

 

[Tenman]

As many miles as he has on that bike. He should be able to listen to it grind and tell if it's slow.

 

[Jlq1969]

The decompression device will be activated (1 exhaust valve held partly open in each cylinder) at cranking rpm to reduce the load on the starter, that is the purpose of the device. It will de-activate somewhere above cranking rpm but below idle rpm, likely 500 to 800 rpm. The measure-able compression will be less than if the engine did not have a functional decompression device and the specifications are adjusted accordingly. Holding the throttle wide open would have to be done manually at the butterfly, the twist grip alone doesn’t open the throttle at cranking rpm.

yes… .it is perfectly explained. But if the butterflies are not completely open, there would not be a full charge of air sucked in by the piston, then the compression would not be complete either ... I think the service manual lacked clarifying what the gv550 says about the hand throttle. ... (that the butterflies do not open with the hand throttle until it is at idle) ... also, it is probably necessary to clarify that the psi indicated in the manual, is only reference ... (96 psi is very little for an engine with 11.5 ratio compression)… .so surely the real compression is higher (or because a dynamic component of camshaft is missing)… or because the decompressor is activated at 250rpm… or because the throttles are not open…

 

[Jlq1969]

 

[eheal6520]

Ok as far as the WOT and butterflies are concerned, I intend to try the first compression test with the throttle bodies still not connected, right now they are on a table. Just have to remember to take the rags out of the intake ports.... that might be tough.... Off hand, I'm not sure it will work, but I don't want to attempt to start until I have some compression information to compare to the manual and the numbers the dealer got. I will take a look at the electrical and see if the interlocks will allow the starter to spin. Once I have the compression numbers I can decide to put it together(yea!) and attempt a start (more yea!) or yank the head and do the valve thing (lots of &^&$^%*^) .... Can't do any of this until the cam tensioner gets here, UPS says by Friday.

 

[holligl]

Ok as far as the WOT and butterflies are concerned, I intend to try the first compression test with the throttle bodies still not connected, right now they are on a table. Just have to remember to take the rags out of the intake ports.... that might be tough....

I think I would be concerned about sucking something in...

Like GV550 said, if you get it together and the valve checks are reasonable and it turns well by hand I would button it up to check the compression by the book.

Has anyone done a compression leak test that could be done statically while the valve cover is off?

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[eheal6520]

I think I would be concerned about sucking something in...

Like GV550 said, if you get it together and the valve checks are reasonable and it turns well by hand I would button it up to check the compression by the book.

Has anyone done a compression leak test that could be done statically while the valve cover is off?

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At this point I want to button it up as little as possible to do the compression test. If it fails or is suspect I won't have to take as much back apart. I know it's a risk but if test goes badly and doesn't seal, which I don't see why it wouldn't, I can always button it up. No compression leak test has been done, this is the first time the valve cover has been off. As for sucking something in I will have a screen over the ports, like aircraft do, thanks to good ole Home Depot...

 

[Madhatter]

cant wait to hear the end of this story ,that means a solution and we all want to know.... especially you 'eheal6520'.... good luck.

 

[holligl]

No compression leak test has been done.

Sorry, that was a question to the larger forum community rather than you. Has any one else done some form of a compression leak test that doesn't involve cranking the engine at starter speed? IDK how the decompression system operates, or whether it is even possible. It might even be risky to try if your socket slipped.


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[eheal6520]

And the saga continues.....
Good news, I have installed the new tensioner and everything with the cam chain seems to be OK.
I checked the valve clearances and this is what I got. Yes I followed the manual....

All of the intake valves are in spec, although one is a little tight. Actually now that I think about it, 3 are a little loose. Mid-point of the spec being .130mm
Now the exhaust is another story the mid-point in the spec is .250mm. All 4 are WAY off with one being less than .051mm. I think this one never closes because I hooked up the compression gauge up to both cylinders and #1 never gave any reading while #2 got me to about 20psi when I hand cranked it. No point I see in attempting a compression test with the starter.
@holligl, the 20psi in cylinder #2 held steady for the 2-3 minutes while I futzed with other things. Just an FYI...
So, all things considered I think I need to pull the head and replace the exhaust valves...

Any words of wisdom?

Oh yea, on a good educational note, I now know how the decomp on the exhaust cam works!

 

[Jlq1969]

I think that with 135k miles ... probably not only have to change the exhaust valves "only" ... surely the seat of those valves are "worn" or twinned with the wear that the valves had. "Maybe" the valve guides are within the range ... but the seats "surely" are not. “Maybe” it is not necessary to change them, but “surely” it is necessary to seat them at the closing angle of a new valve

 

[Jlq1969]

anyway… .there are some “inconsistencies”… .1) the cct may be damaged, in this case the damage is “usually” on the oil pressure seal, not on the cct's internal spring. This pressure keeps the cct from permanently “bouncing” and maintains a constant thrust on the chain. If the seal is broken, the cct will start to bounce and you will feel the pounding… .but they hardly change the timing in the timing gears “always turning forward”
… 2) you say that suddenly I did not start… .you took it to the dealer… .This “measured” the compression and gave it X values and now you measure the compression… .and you are far below those values… .
.3) something happened between the first measurement and the second… .or something happened “at the end ”From the first measurement… .
4) look again at the marks on the gears you sent… that exhaust shaft is backward… .the only way to slow it down is by turning the engine“ backwards ”… ..the chain on the side From the front it would be “loose”… .and without pressure on the exhaust shaft… .when you start the engine… .turn forward but the chain is loose… .on the other hand, on the intake side, the chain will always be tensioned ( go forward or backward) …

 

[holligl]

Have the valves ever been adjusted in the 135kmi? If not you may have experienced the results. My guess is the one worst valve (.051) is the issue, not seating fully or bent. I would call ~Tabasco and have a chat.

 

[Jlq1969]

My intention is not to add fuel to the fire… ..but I am very interested in knowing “why did the time change in the exhaust shaft”… .bent valves are the consequence …… but I doubt very much that the failed cct is who caused the break
and probably if the cct was failed ... it was for quite some time

 

[AntrimMan]

And the saga continues.....
Good news, I have installed the new tensioner and everything with the cam chain seems to be OK.
I checked the valve clearances and this is what I got. Yes I followed the manual....
View attachment 84037
All of the intake valves are in spec, although one is a little tight. Actually now that I think about it, 3 are a little loose. Mid-point of the spec being .130mm
Now the exhaust is another story the mid-point in the spec is .250mm. All 4 are WAY off with one being less than .051mm. I think this one never closes because I hooked up the compression gauge up to both cylinders and #1 never gave any reading while #2 got me to about 20psi when I hand cranked it. No point I see in attempting a compression test with the starter.
@holligl, the 20psi in cylinder #2 held steady for the 2-3 minutes while I futzed with other things. Just an FYI...
So, all things considered I think I need to pull the head and replace the exhaust valves...

Any words of wisdom?

Oh yea, on a good educational note, I now know how the decomp on the exhaust cam works!

Bent valves would be stuck open and the follower clearance measured would be greater than standard. Check your measuring method for errors.

 

[eheal6520]

anyway… .there are some “inconsistencies”… .1) the cct may be damaged, in this case the damage is “usually” on the oil pressure seal, not on the cct's internal spring. This pressure keeps the cct from permanently “bouncing” and maintains a constant thrust on the chain. If the seal is broken, the cct will start to bounce and you will feel the pounding… .but they hardly change the timing in the timing gears “always turning forward”
… 2) you say that suddenly I did not start… .you took it to the dealer… .This “measured” the compression and gave it X values and now you measure the compression… .and you are far below those values… .
.3) something happened between the first measurement and the second… .or something happened “at the end ”From the first measurement… .
4) look again at the marks on the gears you sent… that exhaust shaft is backward… .the only way to slow it down is by turning the engine“ backwards ”… ..the chain on the side From the front it would be “loose”… .and without pressure on the exhaust shaft… .when you start the engine… .turn forward but the chain is loose… .on the other hand, on the intake side, the chain will always be tensioned ( go forward or backward) …

1- the CCT has been replaced with a new one and gasket.
2&3- the dealer did a normal compression check which would have used the starter motor to spin the motor. The 20psi result I got was from turning the crank by hand after the CCT was replaced and the cams realigned.
4- not sure how it got there.. it is possible that there was slack on the chain and valve tension on the exhaust cam that might have forced it forward. Anyway moving the exhaust cam CCW is what I did to realign it. The intake cam was never out of alignment.

 

[eheal6520]

Have the valves ever been adjusted in the 135kmi? If not you may have experienced the results. My guess is the one worst valve (.051) is the issue, not seating fully or bent. I would call ~Tabasco and have a chat.

No, the valves have never been adjusted. This is the first time the valve cover has been removed. I know in retrospect it should have been done but I never took the time. Let the A$$ kicking begin!

 

[eheal6520]

My intention is not to add fuel to the fire… ..but I am very interested in knowing “why did the time change in the exhaust shaft”… .bent valves are the consequence …… but I doubt very much that the failed cct is who caused the break
and probably if the cct was failed ... it was for quite some time

The probable result I agree with, as for the exact cause I haven't a clue. Research here on the forum suggests a bad CCT, perhaps it only jumped one or two links at a time and I just never notice and chauked up the occasional hard start to flooding as the WOT would get her started.

As far as adding fuel to the fire goes, have at it. If I didn't want anyone to know I would have kept it all to myself and certainly not posted on the forum. But, I know there may be some educational value for both myself and others as well as a hole bunch of entertainment value!!!

 

[eheal6520]

Bent valves would be stuck open and the follower clearance measured would be greater than standard. Check your measuring method for errors.

That is what I expected. I measured at TDC per the manual but you bring up a good point and I will recheck. It was bugging me in the shower this morning as to how it could get tighter and only one valve....

 

[holligl]

Did you check the compression without the exhaust cam in place? You might consider rechecking the measurements and adjusting the valves before removing the head. You might get lucky.