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Library Home Page > 1st Generation (1983 to 1993) > Suspension
CLASS System Overhaul
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CLASS System Overhaul

If you remember, I posted a week ago or so that I was having problems with the CLASS air compressor on my '88 Royale. From 0 psi, it would pump the rear shock to about 52 psi before giving an error E3, compressor on too long. From 43 psi, it maybe jump to 44 psi just before stopping with an E2, air pressure not increasing.
No one responded back, so I guess no one has had a problem, or at least not attempted to fix it. So, I thought I would delve into it myself. It seems to me that my compressor was working, but just could not produce enough pressure or enough volume to satisfy the CLASS computer's diagnostics. When an engine losses power it is usually a blown head gasket, burnt valves, worn piston rings, or internal damage. Since the compressor runs, I didn't think it would be internal damage, and since there is no combustion, there is no way to burn valves. The next step was to pull it out and see what I could see.
Removing the assembly was pretty easy. There are three electrical connectors to remove, the one to the compressor motor, the one to the bleed valve, and the one to the manifold assembly. You also had to remove the banjo fitting for the front and rear air lines. (Remember to drop the pressure to 7 psi before doing this).  Then the whole compressor/valve/drier assembly lifts out off the the studs that the cover attaches to.
Next, you need to remove the air line from the compressor to the drier, but there are no union-type fittings.  So I first disconnect the union at the valve, then loosened the clamp for the drier and removed the air line fitting on the drier that goes to the compressor. I then removed the compressor from the mounting bracket.
Finally, you can get a wrench in to remove the air line. OK, so I clamped the compressor in a vice, with the head facing up. I removed the four screws and pulled the head. There were two thin pieces of metal that formed a reed valve of the intake port. I removed them as well. The body of the compressor contains a sintered iron insert that acts as a cylinder. The cylinder head seals to that insert by way of an o-ring. The O-ring looked OK, so I went on.
I then clamped the compressor in a vice so that the motor was sticking straight up. There are six screws facing upwards. The middle two only secure the motor to the body and do not need to be removed. I removed the outer four screws and separated the compressor case. The motor side has a simple gear reduction from the motor with a small crank pin sticking out. The piston and rod will be lying in the bottom half of the case. I pulled the cylinder/piston assembly out the head end and then pulled the piston from the cylinder. After washing everything in solvent, I could see no damage. The piston has a single teflon looking piston ring on it. Just eyeballing it, the piston ring didn't seem to stick out much from the skirt and I was so confident that Yamaha would not sell a replacement, I wondered how I could make it thicker. Some oil rings on automotive engines are multi-piece. They have a wavy steel spring that fits in the groove, and then the oil ring sits on top of that wavy spring. The spring presses against the oil rings forcing them outward. So, I took a piece paper and cut a string 1 7/8" long (the circumference of the piston ring groove) by 1/8", the width of the ring) and placed it in the groove and then put the ring on top of it. I then put then slid the piston back in the cylinder. Too tight. So I measured the thickness of the paper, .005".
So I went on a hunt and found some that that thin tissue paper that my wife buys to stuff in Give bags. It measured just a touch over .001". So, I cut a strip from there the same dimensions and gave it a try. Again, I put the piston in the cylinder and felt a little bit of resistance, but not too much. I lubricated the piston with a very light coat of Vaseline and place the piston in the cylinder, and then put the cylinder back in the compressor housing. Next it put a little moly grease on the crank pin and a very thin coat of RTV on the mating surfaces on the compressor housing and reassembled the compressor, making sure that the crank pin went into the piston rod.
I cleaned the reed valve inserts as well as the head. I put the reed valve inserts in the recess at the top of the cylinder, making sure that the alignment notch was properly oriented. I then cleaned the head and put a thin coat of Vaseline on both the intake port and the o-ring. I couldn't readily figure out how to clean the exhaust port. There is a bolt on the top of the head that presses on a spring that closes the exhaust port. I removed the bolt and the spring, but the valve stayed in. Oh, well. So I put the head back on and tightened the screws. I then reassembled everything else and put it back in the bike. Flipped the ignition to accessory and presto, it pumped up to 70 psi and shut off, just like it was supposed to. I bled the pressure down to 43 psi, and again it pumped back up to 70 with no errors.
Further more, since I discovered the progressive front end that I have and found that I like the handling better with no air pressure in the forks, I left the front air line disconnected. I capped the air line by placing two rubber washers, one on each side of the banjo fitting, and bolting them together with a 1/4" bolt and two steel washers. That will keep any dirt or moisture out of the air lines. On the valve side, I bought an M8x1.0 bolt and cut it short, probably 15-20mm and screwed that into the valve seating it against the o-ring. I saved the banjo bolt in case I wanted to make it work again.
The whole operation took less than a hour and didn't require any special tools, other than a micrometers to measure the paper. Worth a shot if you compressor starts to lose it's ooomph.
.............Larry Piekarski,  '88 Royale

P.S. My apologies to the Canadians on this list that have to suffer through those measurements in our screwed up measurement system. :-)


Last update: 03:29 PM Sunday, September 26, 2004

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