Compression Issues with XJ550RJ

This thread is just to figure out what's going on with the compression on my Seca.

I'm pretty sure that I need a valve adjustment, but I'm not sure if that's the entire problem.

The bike had been sitting for about 4 years when I bought it, so stuck rings are a possibility, too.

I was only able to get out the spark plugs for cylinders 1 and 4, so the readings are as follows:

Cylinder 1: 50 psi
Cylinder 4: 30 psi

These are alarmingly low values, but I held the throttle wide open and the bike was ridden about half an hour before.

Also, I went through the carbs and everything seemed golden. No dirt or gum, and every single hole was perfectly clear. Just for good measure, I sprayed some cleaner all around every passage hole I could find to help with my performance issues, but nothing seemed to change as far as performance goes. Still choppy down low, poor idling, poor high speed power, etc.

 

Are you sure your compression gauge is good? It is not even supposed to run with comppression this low. Did you have the engine turning until the readings didn't go up anymore?

 

It's possible that the gauge is not working correctly. I'll test out some of the other motorcycles I have to see if it returns proper readings in that case. And yes, I did turn over the engine about 15 times because I thought it would increase the reading to what's accurate, but after about 4 rotations it leveled out at the values listed in the OP.

 

Yeah the compression gauge is bad. I also found a large metal shaving in the adapter >.>

Read my mom's rebel at a whopping 30 psi.

Won't be buying from that company again, but I will try to get a replacement from the store or my money back at least.

 

AutoZone has gauges for rent if there is one in your area.

 

You'd better get your money back, you could put it on a good tool.

 

he will be lucky if they have a 12mm tester

 

550's are 12mm plugs , I was not aware of that. My 650 and the rest are all 14mm long reach plugs

 

Yeah I think the compression tester is just a bad model. I returned the one I had and got a new one from the store. Still read about 50 psi on cylinder 1. At this point, I gave up. I'll just get my money back tomorrow. Hopefully my bimmer uncle will have one that I can use for free.

 

Ok, so I borrowed a real compression tester from my uncle and I got about 120 and 110 psi in cylinders 1 and 4 respectively. I will assume that two and three are fine, around the same. I won't really know until I buy a deep socket to get out those buried plugs and get that gauge hose in there, but I think it will be safe to ride until I get a valve adjustment done.

Oh! And my clymer manual said 130-160 psi is ideal, so this could be an issue, but I'll glance over it for now.

 

It will not be safe to ride until you get a valve adjustment done. Unless you are sure that the valve clearances are in spec the bike should be parked. Tight valves will still give good compression readings. Tight valves will also burn.

 

By tight do you mean small gaps? Because that would make sense contextually. Anyways I am letting the bike cool tonight and I will check them first thing in the morning with my uncle's (yeah) thin feeler gauges.

 

Yes, I mean small gaps.

 

Overnight stone cold.
METRIC feeler guages from.20mm on DOWN

 

Alright, so I took apart my tank and cover and all that to get to my valve shims. about 75% of them are in spec. I'm not sure if I measured perfectly or not, but I tried to get the lobes as far away from the shims as possible by rotating my wheel forward in top gear. The other quarter of the valves are too tight I think. I used the smallest gauge in the set of gauges that I picked out within specs, and it either felt tight or wouldn't even go in.

I have a shim tool in my cart at Amazon, so I will eventually fix these tight valves, and remeasure with the shim numbers, but today I just wanted to get an estimate. What I found concerns me, because I'm now worried about valves floating or not closing and opening on time.

 

Try not to worry so much. Park the bike until you can get the needed shims to put everything in spec.

And here's how you do that: http://www.xjbikes.com/forums/posts/122016/

Valve float only happens at excessively high RPM (above redline). Valve clearances have only a very small effect on valve timing; you will not cause a valve to hit a piston by hiving valves out of spec. The big issue is the exhaust valves not getting a chance to cool off because they won't be opening far enough to allow the exhaust gasses to flow well. This is a robust engine design, and even tight valves are only rarely damaged.

You will want to order a thin shim to put into the buckets of the valves that you can't get a feeler gauge into so you can measure the clearance.

You do not absoultely need the shim bucket tool. A length of insulated solid coper wire, or a zip-ty can be used instead. Fitz covers that method in his above thread.

 

Do you think that a valve adjustment could fix some of my performance issues as listed in the "Hello! And a few problems with my 32 year old Seca" thread? This probably sounds like a dumb question, but it's really the only sign I have of my not perfectly functioning engine.

 

After your valves are inspec you can do a proper running synch of your carbs.

 

What he said^ valve clearances are a critical component to the combustion process.

 

Thanks for your quick responses. I bench synced my butterfly valves a few weeks ago, which did seem to help my idling troubles, and I'll be sure to adjust my valves and sync my carbs soon.