Horrific loud chain noise on cold startup

[VanIsleFJ]

I've got a 1990 FJ1200 which I put together from two bikes. (Other one is 1989) It's my first one, but not my first bike and I'm an relatively ok hobby mechanic. The engine and frame serial numbers don't match so not the original engine?  The odometer shows about 35800 kms and I've put about 3500 kms on this myself, all of it last summer.  Compression test showed 160 to 165 psi across all cylinders.
The engine has always be a little cranky with some chain noise at cold startup but quiets down when warmed up. Today I put about 30 kms on the bike after it had been sitting for close to 3 months. The chain noise was so loud and loose sounding for close to two minutes I was worried it was going to come apart.  Oil level is correct.  It did quiet down and could be easily revved to 7500 rpm.
Starter chain?
Cam chain?  I think not as it sounded so bad you would think it would have affected timing.
Ideas/experience with this?
Thanks.

[VanIsleFJ]

Also, it's got a new small oil leak near the oil filter which I'll be inspecting when changing the oil in the next week or so. I can't see this being related at least I hope not.

[fj1289]

Problem could be enough slack in the starter chain to slap the starter clutch oil nozzle. 

This nozzle is designed to prevent that

https://www.rpmracingca.com/proddetail.asp?prod=UpgradedOilNozzle

[VanIsleFJ]

Thanks very much!  Figures I just placed an order with RPM.  Is it a significant tear down to install this part?

[fj1289]

I don't know - maybe Robert or Randy has a trick without splitting the cases?   

[VanIsleFJ]

Thanks again.  I did find a thread which suggests removing the alternator (generator?)  Maybe that is the solution.

https://fjowners.com/index.php?msg=203343

[Old Rider]

i had bad noises in engine to and also have converted to the xjr 1250  short oil jet nozzle while in there. I think you can replace the oiljetnossle with out splitting the engine. you can also replace the camchain with a chain with masterlink .i did that once https://fjowners.com/index.php?topic=18143.210   you should also check your camchain tensioner first .

[VanIsleFJ]

Thank you Old Rider.   That is some serious work you did in splitting the cases and well done write-up too!  If I need to do that I will first try to use the spare engine I have, with presumably 58000 kms.   I've not tried to fire that one up.  It came in the 1989 parts bike I bought with my 1990 FJ.