phil.

In a previous thread I asked how to adjust the cranks so they were OOP (out-of-phase). So I loosened the EBB (eccentric-bottom-bracket) last night and derailed my chain, adjusted the cranks OOP no problem. So now I'm wondering what's the best way to get the desired tension in the timing chain. It seems like there might be a tool out there that fits in the two holes on the non timing ring side of the EBB where you could twist to apply leverage to get the desiered tension.

I don't know it just seem shard to get it set to where there is only 1/2" of play in the timing chain w/out something for leverage. I'm guess it exisits, if so should it have been included w/ my tandem purchase (burley tosa)? If not where can I buy one?

I have a set screw type EBB - was just checking out sheldonbrown's website to see if he had any info on this subject...no such luck. Also if anyone can tell me what torque setting the set screws should be set too that would be great (from sheldon's site it mentioned that you can indent the eccentric part if too much torque).

Thanks,
phil. (looking forward to trying an OOP ride soon).

TandemGeek

The tool is a Park SPA-1 (Green) Pin Spanner.
https://www.parktool.com/tools/SPA_1.shtml

However, in most cases you can set rotate your eccentric by hand to get the proper tension.

Also, if you set the tension to get your 1/2" of play before you tighten the eccentric you'll most likely find that the chain will be too tight after the eccentric's retention bolts are tightened down. This happens because once the eccentric loose the front bottom bracket axle is pulled back towards the rear cranks by the weight of the chain. As the eccentric is tightened, the whole assembly self-centers in the eccentric drop-out and the bottom bracket axle moves forward a few millimeters.

Therefore, to get the proper tension you need to rotate the eccentric while it's loose to get the proper tension for your 1/2" of play, and then rotate it a few mm's to add enough slack to compensate for the front bottom bracket axle's forward movement when the eccentric is tightened.

You'll also note from my previous post on this subject that timing rings aren't always perfectly centered on the timing cranks which can create "high spots" and "low spots" for the chain's tension. You'll want to be sure that any high spot isn't so high that it takes all the slack out of the chain during a full rotation of the cranks.

Engraver

I'm a new recumbent tandem rider, Greenspeed GTT. I changed my pedals so they were out of phase by 90 degrees last night by loosening the boom. My quesiton now is how tight the timing chain should be? I pulled it very tight. I noticed in this thread that you mention the chain should have a 1/2 inch of play. Is that 1/2 inch in either direction, or total? Would that also apply to my bike?

Thanks

TandemGeek

The 1/2" total is an approximate value for obtaining enough slack to allow your cranks to turn freely and without binding, but not enough to allow the chain to self-derail under hard pedalling. If you have perfectly round chain rings you could conceivably get by with less slack.

zonatandem

A pin tool should work in the two pin holes. You local bike shop should have one or check a catalog or website.
Some eccentrics have a larger round hole, in which you can insert a Phillips or small headed flat screw driver; use the crankarm bumping against the screwdriver blade to get the desired chain tension. Then re-tighten the two allen setscrew bolts.
Max chain 'bounce' should be around half inch. Rotate pedals backwards and check chain in several positions, as chain rings are not absolutely round.

Pedal on TWOgether!
Rudy and Kay/zonatandem

Pedal on TWOgether!
Rudy and Kay/zonatandem

AD-SLE

Rushed post. I discovered my timing chain has become loose after I acquired it used. When I first got it, it was too tight IMO. But, not wanting to fiddle with something that was not broke, I left it alone. Now, 300 miles later, I have developed over an inch of total slack. I have looked at my eccentric BB and saw some rather ugly marks on the ALU eccentric body. In short, the two pin holes look to have been hammered on with a small drift pin which now precludes me from using the proper tool. Bike is a Burley Duet.

I have a big ride in the AM and need to sort this out tonight but have not done as much resarch as I would have liked. I hope all goes well but thought I would proactively solict advice.

I will loosen locking allen head set screws and hope things rotate by hand and adjust to the 1/2 inch total play. What if things don't turn easily? I can imagine that if this ALU body has moved while the set screws are engaged then likely there is a big sloppy groove where the set screw presses against the ALU and I'll be doing this every 300 miles?? Since it is currently located "high" (above the horizontal plane) I recall reading good form is to locate "low" to reduce center of gravity. Seems anal and as such I will call it "good form". It might also buy me fresh ALU to engage set screws? Or, it was there and someone rotated above the plane to get better engagement? Thoughts? And does the fact it became loose suggest other concerns?

Perhaps my worries are for not. I'm a newbie in this area. Any advice welcome as I sweat over the Duet this evening.

A big THANKS! I meant to post this last weekend.

AD-SLE

Update: Did the basics. Fortuneatly the pin spanner tool still engaged in what remains of the butchered holes. Thankfully. It took some torque to rotate. Moved it below the horizontal plane and adjusted to suit. The set screws did not appear to have multiple "engagements" with the ALU body so I just adjusted, torqued with some extra and hope all works for the 50 mile ride in the AM. Seems my worries were just that.....but I will let you know after the ride!

TandemGeek

When not pressed for time, it would be a good idea to pull one of the front cranks off so that you can completely remove the eccentric from the eccentric shell for a good cleaning and lube of both components.

bockwho

I would recomend lube also .. .. on the old burley ive improvised by using two drill bits and a drift of screwdriver. ...