New cam chain causing slow cranking?

eon · Dec 6, 2004

Hi all,
Since installing the new follower bearings and new cam chain the starter struggles to turn the motor over. I first thought the valve clearances had loosened due to settling in etc but ther're OK, the only thing that I can think is that the (slightly) different valve timing due to the new chain has amplified the effects of normal wear of the the decomp lifter, does this sound right?

Ian

Taffy · Dec 6, 2004

needs a good run eon i think. if not you may have got the cam timing wrong at one of two places. the first is the gears in the sidecover. use a ruler and squint yer eye to check this.

next is the cam and to do this you need to look at the engine timing marks through the inspection hole. get the first mark 10mm to the left of the marker and that means the 2nd one will be 5mm past the marker. this is as good as dammit TDC.

take the rocker cover off and both cam lobes should be like mickey mouses ears and level with the cylinder head (not the workshop floor!).

you'll be one (half) tooth out somewhere. as lineweaver has said the gears in the sidecover represent half a tooth (or mistake!) whilst the camwheel speaks for itself.

good luck!

regards

Taffy

eon · Dec 7, 2004

Taffy,
What I did was attach the new chain to the old one and feed it through then with the timing marks aligned for TDC on the flywheel I positioned the cam sprocket (lobes up) so the screw holes were vertcally in line with the cylinder. I haven't messed with the gears inside the cover so they should be good. Should be straight forward right?

Ian

Taffy · Dec 7, 2004

....and then you may have fitted the tensioner, the cam rolled slightly back whereas it may have been tilted slightly forward when you dismantled.

difficult to feed a chain on with the cam in situ-***** infact-i'm afraid i shall have to ask you to accompany your bike back into the garage sir!

sorry!

coronaberg · Dec 7, 2004

chain

You are going to need to remove your camchain tensioner and reset it as it snapped out for your old chain. Do not try to run it in,you will wear out the chain guide!

Simon · Dec 8, 2004

For what it's worth I would go back and install the cam at TDC with the lobes pointing downwards and check the timing from there. At least then you are working from TDC on the compression stroke.

It is quite easy to slip a tooth or two on the shaft when feeding the camchain round so it is always worth having the clutch casing off to correct any problems there. In addition, you then also have the engine timing marks as good timing indicators, not just the flywheel.

Cheers,
Simon

Taffy · Dec 8, 2004

simon

once in every two the timing gears do line up!!!!!

and if you do put the cam in with the lobes down-where is your visual on that and especially when he puts the cam cover back on!!!

not your best one there mate :?

Taffy

Simon · Dec 8, 2004

Well Taffy, perhaps sometime you should try being a little less sure that only Taffy knows the way :wink:

I don't want to start an "I'm better than you" thread but I've
changed and re-timed a fair few Husaberg camshafts, not only on my two engines but others too. I kind of suspect I've probably done it a fair few times more than you have.........

I any case, nobody needs to rely on my advice alone - just read the Husaberg workshop manual - even that says install the cam with the lobes pointing downwards.

As for visuals, you should look a little closer Taffy, they're there and more than obvious enough for anyone to use (accurately) :wink:

And for those who are less initiated in timing their engines, and in my humble opinion, always time the engine up with all the timing marks in place at tdc on the compression stroke. At least then all the markers are in place and you know exactly where you started.

It's a free world though and anyone's free to do it how they want :wink:

Cheers,
Simon

Taffy · Dec 9, 2004

i'm not denying your ability to get there and get the job done it's just the way you've put it. you say:

"always time the engine up with all the timing marks in place at tdc on the compression stroke"

but the timing marks always line up at TDC and it's only the compression stroke cos you fitted the cam with the lobes down and not up!

the thing husaberg are protecting you from is simply trying to cram the rocker cover on with the lobes sat at 5 to 1 (is that am or pm?) and to get around that i turn the engine one revolution and fit the said cover.

can we agree that the timing marks in the ignition side aren't actually at TDC then? neither of them? this is what you imply i'm just thinking that you've never done the D-S test.

i'm with you it's those others!

regards

Taffy

Simon · Dec 9, 2004

Taffy said:
"always time the engine up with all the timing marks in place at tdc on the compression stroke"

but the timing marks always line up at TDC and it's only the compression stroke cos you fitted the cam with the lobes down and not up!

Doh, of course it's the compression stroke because that's the way the cam is fitted. It is also meant as a general rule of thumb "for the less initiated" (and also some that are more initiated too :wink: ). This is good practice for any work being carried out where it's relevant.

How many people have come onto this site after having problems with engine timing because they didn't time it all up correctly - i.e. on the compression stroke - when they took the bleedin engine apart?

Taffy said:
can we agree that the timing marks in the ignition side aren't actually at TDC then? neither of them?

We can indeed. I never use the marks on the ignition side to set tdc, not even to do a valve adjustment.

Taffy said:
this is what you imply i'm just thinking that you've never done the D-S test.

I'm not implying anything of the sort. I was actually suggesting, if you read my first post, using the engine timing marks as good timing indicators, probably because that's exactly what they are :wink:

If, what you mean by D-S is the dead stop method you'd be wrong. You make a lot of assumptions, often incorrectly so.

Cheers,
Simon

Taffy · Dec 9, 2004

i'll get you trained up yet simon! :twisted: :wink:

Taffy

BundyBear · Dec 9, 2004

Whatever procedure you use, if you do noting else MAKE SURE you wind the engine G-E-N-T-L-Y through several turns by hand prior to hitting the button or laying the boot in. If you don't, a minor foh-pah can quickly turn into an expensive head-job.

(can I say that?).

For what it's worth, a good check for TDC with the LH case on is to use a prong (eg calipers) down the plug hole on top of the piston. It will also give you more confidence in the TDC timing marks.

eon · Dec 9, 2004

Thanks fellas for the comments, I admit I don't quite understand all of what has been said but that is good because it has made me go back to the manual and get it straight in my mind. Just for clarity and hopefully for other people's understanding I would like to outline what I think is obvious/logical.
For starters I erroneosly mentioned I worked with the lobes up, the lobes were down (So not sure now why Taffy has the lobes up).
Previous bikes I have worked on have the timing chain driven directly off the crank, the Berg runs off the counter balancer but as I have never touched this I assumed all is OK.
As all the messhing gears concerned with the CB are the same size there is no reduction, that is to say that every one full revolution of the motor are all the same (compression/exhaust strokes don't exist until the cam is installed).
To enable threading the new cam chain through I removed the tensioner and the sprocket from the cam.
So reluctantly I shall take the rocker cover off and check everything, I say reluctantly as I was able to get a leak-free cover seal this time.
So I will make sure the piston is at TDC with a probe and ensure the cam lobes are down. One thing that comes to mind is whether I put the sprocket back on the cam correctly but as I recall there is a decomp stop attached that pretty much determines which way it attaches.
I will also check the decomp device.
The bike is running fine except for the cranking, will let you know what I find, thanks again for the discussion.

Ian

Splat · Dec 10, 2004

Ian,

Before taking apart your motor, reconsider all that has been done and discussed.

First, if you did infact install the cam 180 degrees off (lobes up vs. lobes down), that will pose no problem. The ignition sparks every revolution of the engine crank, so the engine will run the same regardless of the initial lobe up or lobe down position; presuming the cam is off exactly 180 degrees.

Second, if the cam or crank is misaligned by a tooth, the engine will run poorly. You complaint is not poor performance, your complaint is that the starter is having trouble spinning the engine.

A more reasonable explanation is that now the engine has better compression due to more accurate cam timing with a new chain. A worn chain and gear set will allow the valve timing to be ******** a large enough amount to cause a reduction in compression, thus an engine with a worn timing set will be easier to crank and will infact crank more quickly.

More accurate timing with a new timing set will have the effect of increasing the engines compression and thus the starter will spin the engine at a noticibly lower rpm.

Lastly, you may want to check your decompression devices and make sure they are adjusted properly.

eon · Dec 12, 2004

Found the culprit - the decomp spring had somehow "unwound" itself. It seems the job of the spring is to offer enough resistance to centrifugal force for the decomp system to remain active at slow (cranking) speeds but without the spring the decomp weight will just fly-out as soon as the motor starts turning. After adjusting the spring everything is back to normal, infact better than normal which tends to make me think that it's been like this for a while and only made totally noticeable by the new cam chain as per Splat's explanation. I wonder if this is the cause of many of the "poor starting" complaints propmting people to install better batteries etc, might be worth checking if you have a few miles on the clock.

Taffy · Dec 12, 2004

phew!!!

thank goodness it wasn't you then eon...... :twisted: :twisted:

Taffy

Search

Search

New cam chain causing slow cranking?

eon

Taffy

eon

Taffy

coronaberg

Simon

Taffy

Simon

Taffy

Simon

Taffy

BundyBear

eon

Splat

eon

Taffy

Similar threads

Register CTA

Recent Discussions

Recent Discussions