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A A A A Author Topic: Erratic revs  (Read 2166 times)

gm

Re: Erratic revs
« Reply #25 on: 15-Apr-21, 12:13 »
Hi again
I checked the valve clearances and all are within the correct spec.  also checked if they were moving as the wheel was rotated and that was positive.
The plugs have had a tendency to clog up relatively quick say 4-6month (when it was being used regularly) so would you think it possible that one or some of the valves are blocked open by carbon or muck building up?
The readings do seem low although the left one seems consistently low which would account for it not firing.  This whole issue of the left side not working occurred after a long period of inactivity (12months) could that have caused any of these problems?
always grateful for your advice.
gm

gm

Re: Erratic revs
« Reply #26 on: 17-Apr-21, 16:08 »
Hello Gurus
Its getting colder yes. 
I think I may have the wrong title on this thread, it might have been better being named erratic bike.
After a quick chat to Seagrass I attempted to perform (I think its called a Leak down test) to see if the valves were leaking air.  Before I positioned the piston at BDC just before compression stroke I thought I'd start at TDC and watch the pistons go through their movements.  While at TDC I checked the valve clearances and found the exhaust valves were now very tight and no matter how much adjustment to the tappet screw I cannot put a feeler gauge in.
is this another issue or have I done something wrong?
gm

CX PHREAK

Re: Erratic revs
« Reply #27 on: 17-Apr-21, 16:11 »
I think that is your problem. Verify that you are on the compression stroke on that cylinder and readjust the clearances.

Or you are on the wrong stroke now and the exhaust valves are open. Rotate one full turn and recheck. If the clearance is now normal you are {were} on the exhaust stroke. Or the gap is big from your readjustment. There are 2 TDCs in a 4 stroke cycle as they rotate twice to go suck, squash, bang, blow.

If it's not that you may have burned the valves and as they recede into the head they move up taking up the adjustment.

Rotate it through the cycles turning clockwise from the front a number of times and observe what is happening.


gm

Re: Erratic revs
« Reply #28 on: 17-Apr-21, 17:25 »
Thanks CX PHREAK
You were correct.  After going through the cycles a few times I figured where the TDC on the exhaust stroke was and adjusted the clearances appropriately.
I'll get back to attempting the leak down test and see if I can find the problem. 
I still think it will be a valve issue.
thanks again
gm

Seagrass

Re: Erratic revs
« Reply #29 on: 18-Apr-21, 07:58 »
If you think you had the valve clearances wrong try the compression test again and see what results you get.

Seagrass

gm

Re: Erratic revs
« Reply #30 on: 18-Apr-21, 10:47 »
thank you again
after a bit of mucking about we found TDC before power stroke (tell me if that is the wrong terminology) all valves were closed I rechecked valve clearances all good after a minor adjustment.
We then proceeded to BDC before compression stroke with both valves closed tried the leak down test and could feel air coming out of the exhaust header no air out of the inlet.
I'll tighten again and recheck the compression although it would seem the LHS exhaust valve May be the issue.
gm

CX PHREAK

Re: Erratic revs
« Reply #31 on: 18-Apr-21, 13:23 »
Leak down test has to be performed at TDC compression stroke - the same point that you would do the clearance adjustment.

Get all rockers on the rock and do the test there.

gm

Re: Erratic revs
« Reply #32 on: 21-Apr-21, 17:11 »
Good afternoon Gurus I hope you are well.
I have made all the appropriate adjustments and the clearances are correct.  I have rotated the engine a few times and figured out TDCs and BTCs and noted the position of the valves.
The results are similar to last time:

Compression test
LHS Dry = 5psi  wet = 10psi
RHS Dry - 120psi wet= 150psi

The leak down test at TDC Compression stroke (all valves closed) demonstrated most conclusively air loss via the exhaust.

What are your thoughts?
gm

CX PHREAK

Re: Erratic revs
« Reply #33 on: 21-Apr-21, 17:41 »
If valve clearances etc. are correct I'd think you have burned exhaust valves and seats on that cylinder.

gm

Re: Erratic revs
« Reply #34 on: 21-Apr-21, 18:14 »
Thanks CX PHREAK
 I thought we would finish up at this conclusion. so, never having taken on anything this complex before I have a few questions.
if I am going to fix this problem should I
1. check and renovate all valves
2. check and if required replace rings
3. following on from (2) assess the cylinders and if necessary re-sleeve
4. considering the issues with the impeller thread consider replacing the cam shaft
anything else?
gm

CX PHREAK

Re: Erratic revs
« Reply #35 on: 21-Apr-21, 20:54 »
1 - pull the head in question, take a look, formulate a plan based on your findings.

2 - Did your bike use oil? Oil control rings are more problematic with 650s than compression rings. If not an oil burner I'd likely leave it alone.

3 - Unlikely to be needed.

4 -  If you can source another cam {preferably with followers} replacement may not be a bad idea. How confident are you of this repair?

gm

Re: Erratic revs
« Reply #36 on: 22-Apr-21, 15:35 »
thanks for the advice CX PHREAK
it was not an excessive oil user so will leave that alone.
regarding the cam repair I'm about as confident as I was at repairing the starter clutch.  Ignorance is bliss.  what are followers? I suppose I will see what happens as I go and if I can source a cam.  Seagrass said he once had one made or purchased one from a location on the Central Coast NSW.
thanks again
gm

gm

Re: Erratic revs
« Reply #37 on: 09-Jun-21, 15:22 »
Hi Gurus
Sorry this project seems to be taking forever - constant interruptions.
I am at the stage where I'm about to remove the cylinder head.  I'm not sure how to deal with the engine hanger bracket stud. see photo.  is this likely to come out easily or put up a fight.  and how does it go back in. Is there a torque setting or should I use lock tight.  (apologies if this is in the manual and I've read over it).
I didn't want to take it out unless I knew how to reinstall it.
thanks.
gm

CX PHREAK

Re: Erratic revs
« Reply #38 on: 09-Jun-21, 15:36 »
Remove the rad, put a jack under the motor and remove the entire hanger. Then you don't have to mess with the studs.

gm

Re: Erratic revs
« Reply #39 on: 12-Jun-21, 14:10 »
Hi Gurus
Well, I went to remove the head today and found that the hanger bracket (one piece) connects to the head and the cylinder block. Unless I've got it wrong.
So back to square one, its a learning curve that's for sure.
I'm thinking that I mark the stud use two nuts to to take it out (assuming it will move) and then tighten it to the same mark when I reinstall.  I don't know if there is a torque setting the manual is unclear for the stud.
any comments?
gm

Seagrass

Re: Erratic revs
« Reply #40 on: 12-Jun-21, 18:54 »
Graham there is no need to remove the stud and you should probably not attempt it.

You need to remove the radiator from the hanger bracket (remove the radiator all together) and then the hanger bracket from the frame.

Seagrass

gm

Re: Erratic revs
« Reply #41 on: 13-Jun-21, 16:52 »
Never doubt the Gurus

gm

Re: Erratic revs
« Reply #42 on: 13-Jun-21, 17:12 »
hello again
Well,  I've beheaded the left cylinder.  I need to purchase a valve compressor before I can fully check the valves.  But, the valves didn't look as bad as I thought they might.
Although, some of the valves didn't seem to be seated properly and the gasket looked a bit worse for wear.
any comments? please
gm

Onetrack

Re: Erratic revs
« Reply #43 on: 13-Jun-21, 19:16 »
With the head upside down a rough test for the valves is to fill the combustion chamber with neet petrol, does any leek through to the ports?

CX PHREAK

Re: Erratic revs
« Reply #44 on: 13-Jun-21, 19:23 »
I see no sign of head gasket failure.

Nothing is visible with the valves either but I expect when removed the seats will show signs of corrosion or burning given your compression figures and the exhaust being the failed set per leakdown test.

gm

Re: Erratic revs
« Reply #45 on: 19-Jun-21, 10:24 »
hello Gurus
I finally removed the valves.
The exhaust valves were clogged as was the port and the exhaust.
I measured the springs they range from 50.5 - 50.28mm Outer, and 49.15 - 49.55mm inner the shafts ranged from 6.58 - 6.6mm.
So by my guestimate the springs appear to be halfway through their life but I'm not sure about the shaft measurements. I haven't been able to measure any run out on the shaft. should they be replaced?
Is there a preferred solvent to clean these?
In your opinion does the condition of the valves and seats reflect the poor results of the compression  and leak down tests.
thanks Gurus
I hope your having a good day its overcast and cool here with a southerly breeze and rain patches.
gm

CX PHREAK

Re: Erratic revs
« Reply #46 on: 19-Jun-21, 13:01 »
It looks ugly facing the sparkplug which can be typical.

The best way to know for sure is to begin the lapping process with medium paste.

 This will quickly show you if you have low spots - and it looks like you do.

To check for guide wear lift the valve up to approximately it's full opening and rock in the direction of the arrows. A new guide will have no detectable rock. A little is OK but if it slops back and forth likely the guides need replacement. Exhaust guides are often worn. Intakes are usually good.


gm

Re: Erratic revs
« Reply #47 on: 19-Jun-21, 16:33 »
thank you CX PHREAK
GM

CX PHREAK

Re: Erratic revs
« Reply #48 on: 19-Jun-21, 17:38 »
Looking at your picture you may get lucky and you've got carbon holding the valve open.

Good luck.

gm

Re: Erratic revs
« Reply #49 on: 23-Jun-21, 12:35 »
thanks CXPHREAK
But, luck doesn't seem to be with me this time around.  As I cleaned the carbon from the valves I could see the two exhaust valves are a little bent at the head. the two inlet valves seem fine.  There was also some play in the guide for the exhaust valves as well.

Any suggestions as to what my best options might be at this point?

At least I know why the left hand cylinder wasn't firing.  The question begs - how long has this been going on and what would have caused the bending?.
gm

 


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