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SuzukiSavage.com
/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Cam chain tension /cgi-bin/YaBB.pl?num=1572441554 Message started by Armen on 10/30/19 at 06:19:14 |
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Title: Cam chain tension Post by Armen on 10/30/19 at 06:19:14 A bit of history: A million years ago I built an SR500 for a bud that raced it in SOS. Didn't like the automatic cam chain tensioner, as it seemed to me that at full chat, the chain would be pushing back on the tensioner and allowing the chain to flap around. Dismembered the tensioner, and made it manual (bolt and locknut pushing on the chain guide). What I needed was a way to know how tight the chain was getting. I poked a hole in the cylinder on the back side of the cam chain tunnel near the tensioner. Then, we got the bike up to running temp, I removed the cover, and looked through the hole to see how tight the chain was, and adjusted accordingly. Easy, as the tensioner was out in the breeze. I'm converting my Savage cam chain tensioner to semi-atomantic. Pulled the pawl, and am inserting a length or round stock inside the spring to limit the amount of travel back (loosening) that the tensioner has. So, once again, how tight is tight enough? So, I figured I'd do a similar gag on this bike as I did on the SR. For reasons that escape me, I had made a 22x1.5mm flanged nut on the CNC mill. Chalk it up to boredom. I honestly don't remember what this was supposed to fit, so it made the perfect sacrificial nut. Checked on Ebay and found an corresponding aluminum drain plug (with magnet) from the Hu Brung Poo machine works in China for only $5, delivered! Didn't really want a magnet catching stray metal bits, so I bored out the backside of the plug, saving myself precious milligrams! Here is the plug and nut assembled: |
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Title: Re: Cam chain tension Post by Armen on 10/30/19 at 06:20:52 Next step was to poke a hole in the cam chain tunnel. Using a bit of eyeball-o-metrics, I picked a spot, and dug out an appropriate hole saw. |
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Title: Re: Cam chain tension Post by Armen on 10/30/19 at 06:23:25 Next on the agenda was to make a flat surface. Hindsight being 20-20, I realize I should have started with a much bigger hole saw, cut down to the base of the fins and stopped, then gone back with the smaller hole saw. That would have given me a much neater circle. Ah well. So I went at it with a Dremel and cutoff wheel. Actually kept going after this pic, so it was pretty flat. |
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Title: Re: Cam chain tension Post by Armen on 10/30/19 at 06:27:04 Once it was flat and lovely, I cleaned all the surfaces with contact cleaner. Then I mixed up some JB Weld, and goobered up both surfaces. Found a bolt, nut, and a few fender washers and held the whole mess in place to harden up. Tomorrow, I'll remove the bolt, chisel off any epoxy that went the wrong way, and carry on. The rear chain guide is toast, so I'm waiting for the new one to arrive. In the meantime, I ordered a really sexy 30mm socket to hold the nut while I tighten or loosen the plug. Don't want to be wrenching against the epoxy. |
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Title: Re: Cam chain tension Post by batman on 10/30/19 at 08:25:42 Armen , I believe it was Verslagen who determined that when the bike is at temperature the chain tensioner would have to retract 1.5mm to avoid chain stretch . I went with that figure and set mine to retract at about 2.5 mm, that was at 19000 miles (extended the tensioner ) at the time I first found and joined SSC. I've just put my bike up for the season , and now have more miles without the paw and spring, than with it , 38,800 miles on my original factory chain which seems frozen in time ,I have since 19,000 never made any adjustment in tensioner length. I am at this point more worried about guide wear than chain stretch. |
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Title: Re: Cam chain tension Post by Armen on 10/30/19 at 09:17:29 Thanks Batman! |
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Title: Re: Cam chain tension Post by ohiomoto on 10/30/19 at 11:22:56 Did Armen really just drill a hole in his engine?!!!! The only real surprise here is that he wasn't trying to save weight! :) |
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Title: Re: Cam chain tension Post by justin_o_guy2 on 10/30/19 at 18:39:46 I'm waiting to see what he does to the chain guides... |
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Title: Re: Cam chain tension Post by batman on 10/30/19 at 20:24:40 I'm wondering why the front guide is showing all those cracks ,is that normal wear? Do they crack as they wear thin? |
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Title: Re: Cam chain tension Post by Armen on 10/31/19 at 06:50:12 Hey Batman, Thats the rear guide. Can't get the front one out without pulling the head. |
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Title: Re: Cam chain tension Post by batman on 10/31/19 at 10:11:22 Oops! How many miles on the motor/guide? |
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Title: Re: Cam chain tension Post by Armen on 10/31/19 at 18:30:21 Total mystery, Batman. Got the bike in crates and bags. Title said '96, but it had the early style start clutch thingie. |
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Title: Re: Cam chain tension Post by verslagen1 on 10/31/19 at 19:42:45 66554A4249270 wrote:
Why do that? Put another hole in the back for a bolt to push against the back of the guide. |
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Title: Re: Cam chain tension Post by Armen on 10/31/19 at 20:43:07 hmmmm.... |
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Title: Re: Cam chain tension Post by batman on 11/01/19 at 16:31:12 DBM ,has gone that way but I wonder if that won't create a hard spot and localized wear on the guide(?) I often wondered if it would be possible to insert a small high speed bearing ,so it is just proud of the guide in the same relative location, with the same type of adjustment, might work. |
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Title: Re: Cam chain tension Post by DragBikeMike on 11/02/19 at 14:03:03 The special jack bolt is working OK. I have it apart right now for the cylinder base gasket repair. Have 5629 miles on the engine (total), the last 1000 have been with the modified tensioner system. The jack bolt does not seem to be causing any problems with the rear guide. No chain stretch with the tensioner set at 1.5 mm free play. The cylinder grows .025" from about 75 degree ambient to normal ops temp. I took some direct measurements with the cam dropped .125" that show the tensioner extends 2.7mm for every .025" drop in elevation, so it retracts 2.7mm for every .025" increase in elevation. The chain thermal expansion is about one-half of the cylinder. So the relative change in elevation is about .012. That works out to about 1.3mm changes in tensioner plunger position for a corresponding change in cylinder height. The 1.5mm plunger play allows just a tad of give. I set mine up at 1.5 mm based on this data. Its working OK so far. |
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Title: Re: Cam chain tension Post by DragBikeMike on 11/02/19 at 14:06:49 You might want to consider manufacturing your own plunger sans rack. Extend the plunger on the back side rather than the front. That results in maximum engagement with the tensioner housing. It adds stability and makes the assembly more robust. |
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Title: Re: Cam chain tension Post by Armen on 11/02/19 at 16:00:12 Thanks. I will. Do you think it's worth making a way to keep it from rotating? |
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Title: Re: Cam chain tension Post by batman on 11/02/19 at 16:46:47 No matter which end you extend ,the body of the round plunger (cylinder ) will have maximum engagement , the only thing I might add is a tiny hole drilled into the cylinder outboard of the tensioner to relieve any Hydraulic lock, IF it were to occur ( I don't think it will ,as the tensioner is angled downward , but if tolerances are tight air could be pushed out when it compressed and form a vacuum that may pull oil back in as it extends- at 60 mph the tensioner may have the chance to oscillate at 33.4 times per second ,if spring tension allows.) I used a shorter heavier spring hoping to stop or at least dampen any such movement, and ground a flat on the cylinder in the area of the paw teeth ,for it's full length for the same reason. the plunger can't rotate ,it's bolted to the guide.(use Loc-tite) I found there was one other problem I needed to address ,I pickup a ticking noise (new) and pull the side cover to find that the tiny clip holding the tensioner base missing ,and the tensioner , trying to move off the stud (it can't), but slightly misaligning the guide. I removed the stock bolt , and using a normal bolt the same length and 3 nuts to spaced it out from the case and supply a steady base (which a aligned it perfectly to the guide) the body is securely head in place, trapped between the nuts a the hex head of the bolt ,that was about 10,000 miles ago. |
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Title: Re: Cam chain tension Post by Armen on 11/02/19 at 17:01:19 Hmm, sounds like a candidate for 7068 aluminum :-) Batman, not sure why you think extending the left end of the plunger won't increase the engagement. Seems like it would to me. As Dr. Ruth would say "Vat Ve are looking for is maximum penetration!". |
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Title: Re: Cam chain tension Post by batman on 11/02/19 at 18:38:29 Armen , what about the spring ? as it also expands inside the longer cylinder it decreases in strength, You're removing the paw ,what you want is a stronger spring but one that still allows a minimum amount of travel ,just enough to not allow the chain to be stretched. I actually shortened the cylinder ,but it remains totally inside the body of the tensioner and allows me to run a shorter stronger spring. The outer end of my tensioner is threaded and adjustable IF chain stretch occurs I can lengthen it ,returning the cylinder to it's same relative position in the body, and the spring to it original length. If the spring weakens over time I have two replacements ,and my springs have been known to work ,at least for the last 20,000 miles , while you may be in the hunt for a longer or stronger spring. If at some point I decide to change to a new chain I can adjust the length of my tensioner extension and be on my way. |
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Title: Re: Cam chain tension Post by Armen on 11/05/19 at 08:21:18 Thought about a tensioner bolt on the back side of the cylinder. Looked at the cylinder (on the bike) and saw what looked like a tunnel for a cylinder stud. Went down to the dungeon and took a look at one of my other cylinders. The tunnel is for an oil passage. I would want to do at least a 6mm bolt for a tensioner, and that would be pretty tight. So, that means either a 5mm bolt, or running it at an angle. And the whole are has irregular surfaces. Maybe ok for a cylinder in the milling machine, but not on the bike done with hand tools. |
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Title: Re: Cam chain tension Post by DragBikeMike on 11/05/19 at 13:02:37 You really have to put the jack-bolt in the head. There's no oil holes or stud holes in the way. If you use a 5/16-NF continuously threaded rod, it allows sufficient material to install a steel insert so the jack bolt will run in steel rather than aluminum (the aluminum wall is pretty thin in that area). It works nice. Of course, its a job reserved for proper tooling, which means a mill, which means engine disassembly. I'm lovin your approach to the BIG hole in the side of the cylinder. That's some hard-core poor man's machine shop stuff. Looks tidy and professional. Since the nut is flanged, why don't you set it up with two or three #8 socket head cap screws that bear against the flange. That way, you won't have to rely solely on the epoxy to hold it in place. Looks to be plenty of room. It's unclear to me what you expect to see in there. When you remove the inspection bolt you will see the chain and guide, and I'm sure the chain will be in contact with the guide. But you won't know where the tensioner plunger is at. The plunger seems to be the true indicator of impending doom. An inspection port in way of the plunger seems to be more in order. Are you planning to establish some sort of reference measurement that establishes the relationship between the guide position at the inspection hole and plunger extension? I have a new chain, and five old used chains. When I compare the new chain to the old chains, there is almost no discernable difference in length. I'm thinkin the problem here is guide wear, not chain wear. There's even an old post by "Aeres" that talks about a situation where he/she installed a new chain and the plunger still sat too far out. He/she had to re-bend the rear guide to get the plunger to retract. I think the guides relax over time, and of course they also wear. Bucking up the back side of the rear guide maintains the arc. It works good. A quick inspection every oil change will tell you where the plunger sits. If it's out too far, simply screw in the jack-bolt a turn or two and your back in business. It even works with my head dropped .125". That's a bunch. If it works OK under that condition, it will work fabulous with things in the stock position. |
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Title: Re: Cam chain tension Post by Armen on 11/06/19 at 05:14:15 DBM, Thanks for the hint on the tensioner bolt location. Point of the hole was to see how much chain slack there is when the motor warms up. I'll unscrew the plug and lever back against the guide to see if there is any slack when the motor is hot. Since I'm setting up the tensioner without the pawl and a rod internally to limit travel, I want to know that I'm not overdoing the tension. So, this setup will help me determine how much initial slack to set the tensioner up with. If I decide to do this on the 695 top end, that cylinder will get modified in a mill and be a little less agricultural. |
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Title: Re: Cam chain tension Post by Armen on 11/06/19 at 21:06:46 Let the JB Weld set for a few days, then chased out the threads. |
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Title: Re: Cam chain tension Post by Armen on 11/06/19 at 21:08:17 All together now! Have to chisel off some errant JB jiz. |
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