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cam chain length variables??? (Read 71 times)
steveh
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cam chain length variables???
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! ???
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steveh
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Re: cam chain length variables???
Reply #1 - 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?
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bentwheel
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Re: cam chain length variables???
Reply #2 - 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.
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steveh
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Re: cam chain length variables???
Reply #3 - 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!
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Kropatchek
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Re: cam chain length variables???
Reply #4 - 01/17/07 at 05:39:35
 
steveh wrote on 12/31/69 at 16:00:01:
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 Grin
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steveh
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Re: cam chain length variables???
Reply #5 - 01/17/07 at 16:02:38
 
I will measure the new chain as soon as it arrives.
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steveh
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Re: cam chain length variables???
Reply #6 - 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???? ???
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Kropatchek
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Re: cam chain length variables???
Reply #7 - 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 Embarrassed Embarrassed Embarrassed
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steveh
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Re: cam chain length variables???
Reply #8 - 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??
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Kropatchek
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Re: cam chain length variables???
Reply #9 - 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 Grin


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steveh
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Re: cam chain length variables???
Reply #10 - 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?
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Kropatchek
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Re: cam chain length variables???
Reply #11 - 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
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bentwheel
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Re: cam chain length variables???
Reply #12 - 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.
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Savage_Rob
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Re: cam chain length variables???
Reply #13 - 01/29/07 at 08:10:20
 
Is it mostly the guides wearing down then?
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steveh
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Re: cam chain length variables???
Reply #14 - 01/29/07 at 16:22:10
 
'Can't be the guides since I reused my old guides in the rebuild.
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