Help Request - Shims and Camshaft on 1983 XJ550 Maxim

Hello, this is my first motorcycle, and I'm following the Clymer manual to catch up on any maintenance that may have been skipped by previous owners.

The bike has just under 14000 km (less than 100 are mine) and seemed to be running decent. I've rebuilt the front brake system, adjusted drive chain tension, replaced oil/filter, adjusted timing chain tension, and I'm on to checking valve clearance and cleaning carbs now before I move on to syncing carbs. I just want to be sure I'm correctly understanding the following observations before I continue my work.

My valve clearances seem to be very tight. On my intake valves had two measuring in spec (barely), and two over tight, with one at 0.076-0.089mm clearance, one at 0.038-0.051 clearance.

Only one of my exhaust valves was in spec, and the others were around 0.102-0.114mm, 0.139-0.152mm, and 0.127-0.140mm clearance.

Also, the condition of the camshaft is questionable. There's a "frosted" appearance on a couple cam lobes that I confirmed is a very shallow pitting using a pocket microscope. The borders of the machined/polished and unfinished areas of the camshaft are also a little uneven. Photos attached.

So, I have the tool for depressing the buckets for shim removal being shipped now, but I need to clarify a couple things:

1. Is it common for shims to be over tight from factory? To the best of my knowledge the previous owners never put in new shims. There were a few neglected tasks like original brake lines when I got it so it seems unlikely they would have ignored that but put in the effort to pull the valve cover and swap in overly thick shims.
2. Is the camshaft condition a major issue? Can I continue to use as is or is it important to replace or polish the pitted lobes before doing any more riding?

Unfortunately I can't comment on any changed performance qualities of the bike that could be symptomatic of these observations. As I say it's the first I've owned, so I have no point of comparison to notice unusual performance.

Any information or resources to help me interpret these observations that would be very helpful. Thanks all.

 

You will be doing that for a while, as most owners of bikea do absolutely zero required or preventative maintenance. So check everything that should have been done in the first 15,000-km and do those.

Common, normal, and expected issue when previous owners never do any required maintenance. Valve clearances are critical to proper operation and are part of any tune-up procedure. Valves are "slammed" shut by the dual coil springs on each valve, and as the valve rim slams into the valve seat in the cylinder head, it slightly "crushes" the valve seat and thus moves the entire valve further "up" into the head......towards the shim bucket/shim and thus closes the gap between the top of the shim and the cam lobe.....and therefore the clearances close up.

"Tight" clearances are especially a problem on the exhaust valves, as the reduced cam lobe-to-valve shim clearance allows the valve to open sooner and close later than intended, which means that the valve doesn't get as much "seat time" on the valve seat inside the cylinder head.......and that "seat time" bleeds off heat from the hot valve into the head, thus cooling the valve face to a normal operating temperature. Lack of seat time results in burned valves and then the head has to come off and the valves repaired or replaced, etc. Even if the valve faces don't burn, the change in the valve opening and closing times (due to the reduced shim clearances) will reduce engine power.

Cam lobes: that looks ugly, I've never seen that before. Debris got in there (did the previous owners ever change the oil? Probably not.......) or loss/lack of oil pressure. Are the SHIMS that were in contact with that (those) lobes also scarred like that?

At the very least, I would try and polish the lobes (and then remove ALL the sanding debris that is created) to see if that condition can be at least somewhat remedied. Be aware that if the shims you removed from those lobe positions are also injured on their top surface, then replacement shims may suffer the same fate. Valve shims are surface-hardened on the first few atoms depth of their faces to withstand the extreme pressures between the lobes and the shim face.....and if that surface hardening is wiped off due to the cam lobe condition, then it will eat the shim pretty quickly and spread fine metal debris throughout the engine, which will then eat up cam and crank bearings, pistons/rings, etc.


It sound like you've done a lot of the basic services that you need to do, just remember that there may be a number of other hand-grenades lurking within the bike, as people who don't do proper scheduled maintenance also tend to treat their bikes poorly in all other respects, too.

https://www.xjbikes.com/forums/threads/tech-topic-the-real-costs-of-maintenance.14581/

 

Thanks for the insights. I haven't gotten a good look at the shim under that lobe, but I'll be examining it soon.

I'm wondering if the bike sat for long enough that oil drained away from that lobe and it stayed dry long enough to pick up a little surface rust. I've got wet/dry sandpaper on hand from 800 to 2000 grit so I'll give that a try this evening.