the dreaded chains

[FishWick 21]

Only if the cam sprockets jump more than a tooth, which is unlikely unless you're very brutal with the engine. Best bet is to take it easy on 100K until you can confirm they're OK.

From my experience, the 97 on simplex chained engines rarely need doing at 100K as they have solid polymer upper pads....but the head *may* still need doing at this milage due to guide wear.

OBD1 duplex engines usually always exhibit deep scores in the upper pad but 100K....some even sooner. Mine went at 93K.

I replaced the upper pad with 509E though and used the corresponding bolt, 507B. I checked it when doing the cams after 20K's use and the duplex chain 'cuts' it's shape (the partition links) into the pad very quickly (within the first 1000 miles) but thereafter the pad isn't wearing at all.

To inspect the upper pad, you just need to lift the rocker and shine a torch down. If you want a more thorough look at it, you'll have to remove the upper cover plate too.

[acf8181 0]

now, this was an isolated incient i think, but a friends highline had the lower chain snap due to the lower running disintegrating and the chain jamming on the pegs.....could possibly happen at top end as well if the wear got too bad.

[Guest gb_sean]

Thats my thread, still have the busted hands to prove. Only just completing the job now but I did decide to do followers,waterpump as well as chains/tensioners.