Timing Chain Failure

[radicalracer]

I was hoping that I might tap the experience this group to help me with recommendations on how to prevent timing chain failure. I was out this weekend at Miller Motorsports park and during our heat race my timing chain went. The timing was unfortunate...no pun intended.

My concern is that my buddies went out after about 2 hours. Same set up. Heavy duty roller chain. I hear that radical might be going back to the stock chain. Both incidents (mine and my friends) happened on a downshift. The downshift did not over rev the engine in anyway. My engine had about 20 hours on it and is maintained extremely well. Of note, my friend and I had recently upgraded to the closed loop paddle system.

So my questions are:

1 - What is the recommended timing chain setup for durability?
2 - Any coincidence with the closed loop system upgrade and how it cuts out the engine. Perhaps excessively jerking the chain causing it to snap.
3 - Has anyone else had these issues? Any other recommended resolutions?

Thanks in advance.

G

Edited by radicalracer on Wednesday 12th October 00:21

[DarcySmith]

Hi
It wont be the p/s system.That set up is kinder to the car than a human being.Radical have spent a lot of time developing it.When you pull to change gear,it doesn't completely turn off the ignition and fuel,so you get a "soft cut".
My PR6 1440K8 had done 6 hours and went back to the factory for another issue.
A couple of RPE guys walked past and noticed that it has the latest tensioner fitted,and requested that they took the cam cover off and take a look.
That resulted in them finding that the chain was worn,and they replaced it under warranty with the earlier K7 assembly.

HTH

Darcy

[Matt Graham]

I had a stock cam chain break at the end of last year (bone stock 1340cc, dry sumped, in an SR3). At the time I was using the stock GenII/K8 hydraulic cam chain tensioner. I did a bunch of research, including talking to a bunch of engine builders of DSR and CSR engines for SCCA racing, as well as talking to Radical West/Spring Mountain and the folks at Radical UK/RPE.

In the end, I decided the best solution for me was to run the stock cam chain with a manual cam chain tensioner. To this point, I have over 1500 race miles (~30 hours). This includes a 3 hour "endurance" race, and two races on rovals (i.e. plenty of wide open throttle, high RPM running).

This is the product I'm using now:
http://www.hayabusazone.com/tensioner.html

Hope that helps.

-Matt

PS - I have no idea how this might affect the "sealed"-ness of your engine, as I don't run any Radical sanctioned races, so I didn't bother checking.

[splitpin]

I recollect that the K8's problems (in 1475 stroker configuration, but not in standard fare 1340 configuration) were ultimately resolved by fitment of twice revised Cosworth Pistons, a VH hy-vo and an essentially K7 type tensioner which is more forgiving when backing off/being backed off for a gear change.

Edited by splitpin on Wednesday 12th October 15:42

[BertBert]

Yes, isn't this the current working configuration? I'd just phone up the RPE buys and aske them.
Bert

[splitpin]

Believe so.

So said I think the big Psi turbo boys still favour a roller chain over specialist interpretations/versions of Suzi's hy-vo and a manual billet chain tensioner.

[radicalracer]

Thanks for all the feedback. Really good info.

I do like the idea of the manual chain tensioner. It seems like others on the Bussa forums advocate the use of the manual chain tensioner as well.

I will have to see if I can get my local guys to put one in at some point. I would like any feedback on how often you have to adjust the tensioner. Does it require a lot of adjustment after installation?


Thanks,

G

[Matt Graham]

I installed mine myself. There are plenty of threads on the Busa forums (and on the CSR/DSR Forum) about how to install it and how to adjust it. It literally takes less than 30 minutes.

I adjust it every few race weekends, but not particularly often.

Best advice I can give - get a mechanics stethoscope for adjusting the tensioner. It really helps you hear exactly when you take all of the slop out of the cam chain.

-Matt