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Message started by marekbuk on 08/06/18 at 11:43:35

Title: Cam sprocket cracks
Post by marekbuk on 08/06/18 at 11:43:35

has anyone had an issue with their cam sprocket? A friend who's neighbors tensioner 'gave up' after 38,000 Miles. yes! And he has had the bike from new. Anyway he noticed a hair line crack between the bolt holes. BTW luckily the tensioner failure didn’t trash the engine. The friend maintains the bike for his 76 year old neighbour and the reason for the tensioner longevity is probably the fact that the old guy thinks that 50mph is enough for him ;)

Title: Re: Cam sprocket cracks
Post by batman on 08/07/18 at 15:22:12

I believe this is something we've never seen before , but if the crack follows the curve off the gear from bolt hole to bolt hole ,I believe it can be ignored, the holes will stop the crack from growing further in length. If there is more than one crack,or it radiates out from the holes in any other direction but toward each other, I would replace it.

Title: Re: Cam sprocket cracks
Post by marekbuk on 08/08/18 at 06:04:31

Thanks! - I sent a spare sprocket to my friend - from my spare engine. What do you think of that mileage? Its usual to replace the tensioner around 17,000 miles isn't it?

Title: Re: Cam sprocket cracks
Post by Dave on 08/08/18 at 08:04:18

Spare sprockets are easy to come by - lots of damaged heads/engines with no damage to the cam sprocket.

It would be nice to see a photo of that damaged cam sprocket.....I have never seen one damaged in a Savage engine.

Title: Re: Cam sprocket cracks
Post by batman on 08/08/18 at 08:56:31

We don't replace the tensioner ,we extend it , the chain is the problem ,when it stretches the tensioner falls out, but the chain is only stretched to half it's service life ,extending the tensioner( see Verslagen) allows us to use the chain for the other half. Replacing the tensioner with a new one(without extending) will do nothing unless your also replacing the chain.

Title: Re: Cam sprocket cracks
Post by marekbuk on 08/08/18 at 09:01:08

Hi

Yes - thanks again, I did mean replace with a a Verslagen extension to the shaft - as usual I tend to want to use less typing - I;m just lazy I guess :-(

Does seem to be a bad habit thats all too common these days of 'switched on' all the time.

Title: Re: Cam sprocket cracks
Post by batman on 08/08/18 at 09:23:27

Yes 17.000 to19,000 seems to be the limit on older bikes, although we have seen newer bikes, 2005 and up stretch the chain at as little as 6,000 miles ,a lot depends on how the bike is driven ,short trips tend to stretch the chain faster due to more heating and cooling cycles.

Title: Re: Cam sprocket cracks
Post by marekbuk on 08/10/18 at 01:36:27

Dave

Pic attached clearly shows the cracks. also the sprocket was somewhat 'dished' - not flat!

Title: Re: Cam sprocket cracks
Post by marekbuk on 08/10/18 at 01:42:40

Regarding the amount of 'dish' in the sprocket this is what my friend said:

the pics don't show how much the sprocket has "dished" so to give you some idea of the extent i put the sprocket onto a piece of glass,pressed on the outside edge & under the opposite outside edge i was able to easily insert 1.26mm of feeler gauge blades.

Title: Re: Cam sprocket cracks
Post by Dave on 08/10/18 at 04:25:55

From the looks of the gouges the cam chain made......I would think the cause of the cracks is evident!

That cam gear was abused when the chain broke.

Title: Re: Cam sprocket cracks
Post by marekbuk on 08/10/18 at 05:39:09

Sounds like a good explanation :) he was so lucky not to trash the engine

Title: Re: Cam sprocket cracks
Post by justin_o_guy2 on 08/10/18 at 10:27:58

Kinda hard to tell someone who has so much trouble they are actually lucky, but, you're lucky.
That could easily have been a fatality for the motor.

Title: Re: Cam sprocket cracks
Post by DragBikeMike on 08/10/18 at 13:56:59

Mama mia that's one spicy meatball. You didn't elaborate in your post, what happened to this thing? Did the chain come off the sprocket or did it simply snap? Did the tensioner fall apart and jam everything up?

What sort of checks has your friend done to verify that other parts of the engine weren't damaged? I can't believe that thing failed with such vengeance and nothin else took a lickin.

What's the current status? Did he install your replacement sprocket yet? If he hasn't, I think he should do some checks before he tries to run it (or even rotate it for that matter). If the chain broke, or even jumped the sprocket, there's a good chance the piston kissed some valves. He should verify that the valves close all the way and aren't bent.

With the chain off and cam removed all valves should be fully closed and hard on their seat. Remove the carburetor and exhaust header. Visually inspect the valves through the ports to see if you can tell if they are fully seated. Shine a flashlight down the spark plug hole and look through the ports to see if any light is detectable. If all looks OK, you can pressurize the cylinder with air and verify that there aren't any BIG leaks past the valves. Install an adapter in the spark plug hole and connect an air hose to it. Apply about 50 psi to the cylinder. Listen at the intake and exhaust ports to verify that you don't have any big leaks past the seated valves.

If a valve is bent it will not close all the way and you will either see it through the port (if its bent a lot) or hear the air leaking by (if its bent just a little). Either way, if there's any bent valves the head has to come off.

Title: Re: Cam sprocket cracks
Post by DragBikeMike on 08/10/18 at 14:02:30

Additionally, if the sprocket is dished, I can't imagine the mating flange on the cam is straight. The sprocket is bolted hard up to the flange on the cam, if the sprocket bent the flange on the cam probably bent also. If the sprocket cracked, there's a good chance the flange on the cam also cracked. Those cracks indicate that a huge force was transmitted through that sprocket. That would ceritainly indicate big mechanical interference somewhere (like a piston crashing into valves).

Title: Re: Cam sprocket cracks
Post by LANCER on 08/10/18 at 14:59:56

62595443525E454358505D42310 wrote:

From the looks of the gouges the cam chain made......I would think the cause of the cracks is evident!

That cam gear was abused when the chain broke.

Abused ?
Ahhhhhh yes, and that is an understatement to say the least.
And I agree with the last comment by Dragbikemike that the forces involved that did this damage were tremendous.
I’ve seen a lot of engines from parts bikes, most with toasted engines and several where parts were torn apart and thrown about the cylinder. But I have never seen a cam gear damaged like this before.
This is remarkable.

Title: Re: Cam sprocket cracks
Post by taff on 08/10/18 at 16:07:52

the chain came off the sprocket while the bike was ticking over,thankfully.
the head was removed,4 very light indentations on piston crown.
valves inspected & tested,all 4 were fine.
the camchain showed no real signs of damage apart from 1 or 2 very slight tight spots & 30 odd k worth of stretch.
the tensioner had popped but then it would anyway as soon as the chain went slack.
i was of the opinion that the sprocket was out of true due to the dishing & that the chain simply ran off the side of the sprocket,there didnt appear to be enough damage on the chain for it to have jammed up against the sprocket.
thats just my opinion,i could well be wrong.
anyway,one new camchain,a gasket set,a sprocket courtesy of mark ( thank you ) & a lot of very helpful information,courtesy of this brilliant forum & its members ( thank you too ) the savage lives to ride again.
it is on the button,totally leak free & sounding better than it has for at least 15yrs os so.

Title: Re: Cam sprocket cracks
Post by LANCER on 08/10/18 at 16:35:48

If I found four indentations on the piston I would replace the valves just as a matter of course. They may test good and true but I would not want one coming apart miles down the road from a slightly weakened stem and destroying the engine.
They are inexpensive parts.
That’s just me.

Title: Re: Cam sprocket cracks
Post by taff on 08/10/18 at 17:05:14

i agree lancer,ideally i would have but it is owned by a 78 year old pensioner who could couldnt afford to have it repaired.
i did all the work free of charge & i supplied all all the parts at cost price.
he had change out of £150 & that included new plug,oil & filter.
alternatively it would have sat at the back of his shed forever as it means too much to him to get rid of it.
certainly the lesser of two evils,im sure that you will agree lol

Title: Re: Cam sprocket cracks
Post by justin_o_guy2 on 08/10/18 at 19:31:09

chain came off the sprocket while the bike was ticking over,thankfully.
the head was removed,

I guess that means nothing was holding the cam down.

Shazzam

Title: Re: Cam sprocket cracks
Post by ohiomoto on 08/13/18 at 09:10:45

79707C727D617A7B150 wrote:

--------------------------------

I hear what you are saying, but playing devil's advocate...

Truly evil would be if this 78-year-old man or any other person were riding along at high speed and the engine grenades and locks up. Then before they realize what's happening they get slammed to the pavement and they get run over by a truck. :(

Unlikely, but surely not the lesser of all evils.