Identify manufacture date by s/n ?

Can anyone date this 1975 Interstate 850 engine?
serial number is 313425
Would this engine be included in the batch that suffer from the soft cam issue?
Thanks

I've got a MkIIA 3084xx with a soft cam, and from what I've heard (mostly here and http://atlanticgreen.com/index.php?opti ... r&Itemid=4), the later ones are the most suspect - if the problem started with my bike then yours is likely to be affected - taking valve drop measurements would confirm or otherwise

singring said:

Can anyone date this 1975 Interstate 850 engine?
serial number is 313425
Would this engine be included in the batch that suffer from the soft cam issue?

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I think it would be almost impossible to say?

As batches of bikes were not always built in numerical seqence, and I'm not aware of any numbering information that would pinpoint a paricular bike as having a soft cam or not? I think it was just a matter of luck if any particular bike did have one and another didn't?

But not to worry, if your MkIII did have bad cam then it could have been replaced by now, unless it hasn't done many miles?
Also, this isn't likely to be a problem that will occur overnight, or leave you stranded by the side of the road. If you did happen to notice that the performance was slowly dropping off, then it would be wise to check if any of the valves had noticeably less lift than others?

313425 is a 74 model year MK2 or MK2A, I can confirm 310410 does not have a soft cam . Model year 75 started with 325000, so your bike is a late 74 model year build probably sold in 75 and titled as a 75.

kommando said:

313425 is a 74 model year MK2 or MK2A,

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Yes, you're right, 313425 would be too early for it to be a MkIII engine.

Any Commando engine can have premature cam wear but the really scary batch (6000 miles or less) seem to have been late Mk111s. There is a suggestion that they got the hardening completely wrong.

If I was buying a low mileage 1977 build silver Interstate then I'd be budgeting for a cam job.

The situation is complicated because the cams that weren't used up by the factory seem to have been sold off (mainly in the UK I'd guess) through official and unofficial channels for about the next ten years so they could have got into anything.