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General Category >> Rubber Side Down! >> cam chain length variables???
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Message started by steveh on 01/15/07 at 09:20:04

Title: cam chain length variables???
Post by steveh on 01/15/07 at 09:20:04

Today I removed the cam chain from my 97 (engine already partly dismantled anyway) because I had 18mm of tensioner piston showing. Just for fun (!?), I also removed the cam chain from my spare 87 engine (15000 miles) and the chain from the 97 is definitely shorter than the chain from the 87. It got me wondering. . .
Has anybody thought/researched the variables that might affect cam chain length other than cam chain wear/stretch? For example, could the head from the 87 (which was installed on the 97 engine) be slightly shorter? Could the head gasket have been too thin or over-torqued? The chain tensioner guides from the 97 appear to be in good condition.
The bottom line is, I'm wondering if I really need a new cam chain and/or is there anything that could be done other than replacing the chain to reduce chain slack?
Yeah, I know. What kind of warped mind thinks about these things?!!! Guilty as charged! ???

Title: Re: cam chain length variables???
Post by steveh on 01/15/07 at 09:21:53

on a further note, is there any difference between the cam chain sprocket and camshaft between an 87 and a 97?

Title: Re: cam chain length variables???
Post by bentwheel on 01/15/07 at 11:31:34

First off I know 18mm has been bandied about as "end of service life for the cam chain," but I think this unscientific method has too many variables to be accurate. Firstly the measurement of the tensioner piston itself can be ambiguous. Why not count splines instead? Another variable would be the condition of the guides. Newer guides versus worn ones would also change the measurement.
As far as your concerns about a different head, and cam sprocket, I have never heard of changes during the Savage's production run. An old or over torqued head gasket would not make an appreciatable difference in cam chain length.
When building engines, don't take shortcuts. The best way to measure cam chain wear is to measure the chain itself. The service manual gives end of service lengths when measured between 21 pins.
If you are looking to reduce slack in a serviceable chain you should replace worn chain guides.

Title: Re: cam chain length variables???
Post by steveh on 01/15/07 at 16:10:27

The chain measures 126mm, but I am going to order a new chain anyway. I'd like this engine to stay put together for awhile!

Title: Re: cam chain length variables???
Post by Kropatchek on 01/17/07 at 05:39:35

steveh wrote:

The chain measures 126mm, but I am going to order a new chain anyway. I'd like this engine to stay put together for awhile!

Please measure the NEW chain on 21 pins center to center. Eager to now this lenght. Thanks.

Greetz
Kropatchek ;D

Title: Re: cam chain length variables???
Post by steveh on 01/17/07 at 16:02:38

I will measure the new chain as soon as it arrives.

Title: Re: cam chain length variables???
Post by steveh on 01/20/07 at 14:40:55

OK, here are the measurements. I put two nails in a board, hooked the cam chain over one nail and hooked a bungie cord between the cam chain and the other nail to tension the chain. These are measurements for 21 pins, measured center to center:
chain with 15,000 miles (as far as I know. Maybe replaced??): 5 1/32", or 5.03"
chain with 5 k miles: 5.0 inches
new chain: 5.0 inches
Interesting, huh?
Once again I wonder about replacing this chain and whether the tensioner piston will still be at full estension with the new chain installed. The chain tensioner guides looked perfect to me. Maybe there is wear there I can't see???? ???

Title: Re: cam chain length variables???
Post by Kropatchek on 01/21/07 at 09:19:42

Thanks steveh

For us metric guys

5.00 " = 127.00 mm
5.03" = 127.76 mm

Compare this with the

"rejection" lenght of 128.9 = 5.07"

You mentioned the piston extension is 18mm and the guide seems to be not worn.

Now the miljon $$$ question:

Where is the wear? ? ?

The inside of the camchain, the gears or what??

Greetz

Kropatchek :-[ :-[ :-[

Title: Re: cam chain length variables???
Post by steveh on 01/21/07 at 18:20:53

Yeah, that is the question! From the measurements, I could assume that the chain from the 5,000 mile engine showed virtually no wear, yet the tensioner piston was fully extended. In fact, even the chain from the 15,000 mile engine was within spec. If that is the case, I have just bought a new cam chain needlessly.
Here is the only plan of action I can come up with at the moment: reassemble the engine with one of the cam chains and a new head gasket and see what happens with the tensioner. If the piston looks ok, I will deduce that the head gasket and/or too much torque on the head bolts was the cause of the excess chain slack. If the piston is fully extended, as it was before, I will assume. . . ???? guides??

Title: Re: cam chain length variables???
Post by Kropatchek on 01/22/07 at 05:27:57

The guide is the one that wears-out, I think. Assuming that the head is still in place, mean not removed and reinstalled with a new gasket.

Have a closer look on the guide. It took me several close examination before I noticed a slight indentation near the bottom.

Another thought is that the inside of the chain where it touches the gears wears, like chaindriven bikes, where you replace the chain AND the gears.

Reassemble the head and install the NEW chain with the OLD guide and see what you come up with. If the tensioner is still out for more than 16mm, reolace the guide as well.

Greetz
Kropatchek ;D

Title: Re: cam chain length variables???
Post by steveh on 01/27/07 at 15:24:52

Ok, here's the scoop after reassembly: cam chain tensioner now out 8 mm instead of the 18 mm it was out before. I reassembled the top end with a new head gasket, a new cam chain, and the old plastic tensioner/guides. I also used the 97 head that came on this motor instead of the 87 head the po had installed.
So now all appears to be well! Isn't it interesting, though, that when measured according to the popular method (21 pins, center to center) the new chain measures exactly the same 5.0 inches as the old chain?! Does this mean that it wasn't the new chain that fixed the problem? Does it mean that the method we use to measure cam chain wear is seriously flawed?
Who knows what evil secrets lie in the heart of the Savage?

Title: Re: cam chain length variables???
Post by Kropatchek on 01/28/07 at 08:19:07

Proves one thing at least, the camchain.
Maybe the wear is on the inside of the chain and not the pins that cater for the increase in lenght.

Rest my case, i.o.w. I don't know any more.

Greetz
Kropatchek :-[

Title: Re: cam chain length variables???
Post by bentwheel on 01/28/07 at 16:41:16

Hey steveh, did you think to mic the old head gasket and compare it to the new one? Like I said before I can't imagine you gained an appreciable difference, but I am curious.
So you have determined the tensioner becomes sloppy, but the cam chain has not worn. That is similar to a previous posting I made regarding a slipping clutch but the plates are not worn. It seems with the Savage some things are not what they appear. Mechanical repairs require close scrutiny. Good job on the cam chain project.

Title: Re: cam chain length variables???
Post by Savage_Rob on 01/29/07 at 08:10:20

Is it mostly the guides wearing down then?

Title: Re: cam chain length variables???
Post by steveh on 01/29/07 at 16:22:10

'Can't be the guides since I reused my old guides in the rebuild.

Title: Re: cam chain length variables???
Post by verslagen1 on 01/29/07 at 16:45:05

Did I read right? You had the 87 head on the 97 and the tensioner stuck out 18mm?
Then put the 97 head on the 97 with new chain and now tensioner sticks out 8mm.
How about swapping the heads again to check?
It could be that the 87 head sprocket is really worn.
Or put the new chain on the 87. If loose it might be the sprockets or guides.
Then try the old 97 chain on the 87. If its looser then the new, then it's the chain.

Title: Re: cam chain length variables???
Post by steveh on 02/01/07 at 07:04:29

The engine is back together now except for the head cover and the side covers, so I'm going to leave it as is for now. I used the same camshaft and sprockets as were on before, and I reused the plastic tensioners/guides. So the variables were: 97 head reinstalled on the bike (87 had been installed by the po), new head gasket, new cam chain, new head gasket. It's still mysterious to me, but it seems ok now, so I'm going to get the bike back together and see what happens when I put it on the road?

Title: Re: cam chain length variables???
Post by Reelthing on 02/01/07 at 07:24:38

I remember Anderson selling discontinued cylinders awhile back - seemed suzuki had rev'd it along the way but have no idea what was changed

another possible place is the 87 cam "bearings" are worn enough to move the cam sprocket