Fail Safing the Carrera Tensioners

[aigel]

Posting here recently it occurred to me that much information is going away deep in the archives 10+ years ago with nobody looking that far back because often it is all gone to hell with picture sites being obdsolete etc. So, here a re-post of one of the best mods I did to my SC's carrera tensionsers which is not easily found in instructions.

Fail-safing the pressure fed tensioners, the "Jerry Woods mod":

Jerry Woods uses a special tweak to limit travel on the oil fed tensioners. According to Jerry, oil fed tensioners can see very rare failures caused by oscillations of the chains if an engine runs at very high rpm and then abruptly drops to low rpm. Timing can jump and this can lead to terminal engine damage.

For this modification, disassemble the chain tensioners by taking out the grenade pin and then the c clip retainer pin. Remove the spring. (Figure 1) Put it back together with the spring removed and install the tensioner. Measure the total travel between the collapsed tensioner and the fully tensioned idler arm as indicated in Figure 2.

Now remove the tensioner again and limit the total available travel to 1/8" by installing a piece of tubing into the bottom of the tensioner that is 1/8" shorter than the measured total travel. The tubing has to be 5/8" outer diameter and about 1.5 mm wall thickness. This has to be a hollow cylinder, becase oil is flowing through it and the spring has to go through it also, to keep the forces the same. Hydraulic tubing is a good choice but I had found bronze bushings at the hardware store that had the perfect dimensions. Figure 3 shows this limiting tubing cut to length, together with the piston and spring, before it is installed back into the tensioner housing.

Throw away the grenade pin and the C clip retainer because they will not fit with the limited travel, and are not needed once the tensioner is installed. In the unlikely case that you ever have to take apart a Jerry Woods assembled engine, you will notice that the tensioners have the c-clip missing and the tensioner piston travel is limited. According to Jerry, all his engines (even the stock rebuilds) get this final tweak to race proof oil fed chain tensioners.

Figure 1


Figure 2


Figure 3


Cheers,

George

[Trackrash]

Holy update. I have advocated for some sort of search or index for these sorts of old threads. As I agree, lots of people ask questions that were covered years ago and vBulletin's search is hopeless.

That said, I tried to do this upgrade to my new motor and was unsuccessful. When I measured my clearance and took apart my tensioner, there was not enough room to add a spacer!

Later I had a tensioner fail and yes it made noise but did not cause problems.

YMMV

[aigel]

Hi Gordon,

Interesting that you didn't have enough room. That tolerance taken up already would indicate that something didn't stack up to factory spec? Short chain? Different idler? Frankly, I don't know how consistent that "slack" is across engines. It must vary, otherwise there would not be a need to measure the slack.

Cheers,

George

[spuggy]

Originally Posted by Trackrash

Holy update. I have advocated for some sort of search or index for these sorts of old threads. As I agree, lots of people ask questions that were covered years ago and vBulletin's search is hopeless.

But Google's is pretty good, and they've been indexing the site for a long time.

[HaroldMHedge]

I think you can get them from JWE Motorsports.

The other day I spoke with Don at E B S R a c i n g and they had them in stock.