Puggle

A A A A Author Topic: Erratic revs  (Read 927 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

 


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