Issues with the XJ Bobber build

Deleted, update to follow

 

I doubt that the mechanic would eliminate safety items such as interlock switches. As a service manager I recognize the implication and the liabilities should something happen (such as start in gear and lurch, injuring someone or damaging property). I wouldn't eliminate them if I were in their shoes. I would think long and hard about doing that to my own bike, car, or machinery.

I don't think loose exhaust studs will lower the compression. That is a function of the intake charge being squeezed with both valves being closed. Either there is a leak past a valve or ring, or the valve clearance is wrong due to adjustment or wear of components. The latter can restrict the amount of fuel/air entering the cylinder. Less air in, lower compression number.

 

In answer to your single most important question, having the exhaust system connected or not will have NO EFFECT on compression.

When you test compression you're testing the ability of the cylinders, pistons, rings and valves to do their job. You could test it with no exhaust and no intake manifolds, it wouldn't matter.

If your valves are out of spec, then it can and will throw off your compression numbers.

You need to ensure the valves are in spec; and then run another compression test. Numbers that wonky (shouldn't be more than a 10% variation between cylinders, even the "good" ones are weird) generally indicate a need for a valve adjustment.

Get the valves adjusted, and run another compression test. If all 4 cylinders aren't withn 10% of each other, decide if you want to do a top-end rebuild or look for another motor.

Then worry about the wiring.

 

Well got another call from Bluecat motors today. They are unable to get the compression on the #2 & 4 cylinders where they need to be. This time of year they said they aren't able to do a top end rebuild because of their work load (which I completely understand).

I honestly don't have the technical ability to do a rebuild myself, and I am not interested in paying someone $2000+ to do it (their estimate), so I am in a tough position. I love the bike, and have put in countless hours on the modifications to make it look the way I want it to. Unfortunately a bike that looks good but doesn't run isn't of much use to me.

I am not sure where to go at this point. Do I sell the bike to someone who has the ability to rebuild the motor and finish the project? Do I keep the bike and use it as a tool for learning more about how the motor works and how to repair it (I know I won't be able to teach myself how to rebuild a motor, but the motor is of no use to me right now)? Do I part it out? Do I slowly roll it off a cliff? Do I buy another motor (not sure price range on this) and complete the project?

Thanks to everyone on the site for their input, I really was able to accomplish more that I thought I could and the help I have received here has been of great value.

I am now in the market for another 80's Yamaha and hope to give this another shot.

Matt 'Scizor' Steffes

 

Honestly?

Find another motor, or a parts bike with a decent motor in it. All you need to compression test a motor is a compression gauge, a battery and a set of improvised jumper cables. The motor doesn't even have to be in the bike. All it really needs is to have over 120lbs of compression in each cylinder, and they're all within 10% of each other. My 650 was a $400 whole BIKE and it makes within 1-2lbs of 150 on all four, which is why I went ahead and bought it. Twarn't pretty, but the compression numbers are.

You should be able to find a decent motor for well under $300, more in the $150-$200 range. You might get lucky and find a whole bike for that.

I don't mean to take advantage of your misfortune here, but I'd like to point out this is why getting a compression test on a bike you're about to buy (or just bought) is an important first step. PRE-purchase, it can help you decide how big of a project you want to buy. Post-purchase, it can help you make decisions as to what you want to do with that particular bike, before you sink a whole lot of effort into it, only to be brought up hard by a sour motor.

There are LOTS of 650 Maxims out there; I'd look for a donor and do a transplant if you have that much work into it. If either of my 550s puked a rod tomorrow that's certainly what I'd do.

 

+1 to what Fitz said, finding a motor or parts bike shouldn't be too hard

 

Thank you for the input! I have a newly restored hope for my project! I had owned the bike for a few years and one day got a little antsy with it and decided I was going to make a bobber (Mr. Busch Light may have had a little input).

I am now actively seeking a new motor for the bike. Besides looking online, are there any other places I should check for a motor or parts bike? I live close to "The World's Largest Motorcycle Junkyard" and I know they have oodles of XJs, but really don't know if I should look there.

Thanks again, what was one terrible day has now become much, much better.

 

Heck yes! Take a fully charged battery, your compression gauge, some form of jumper cables and only as much cash as you're willing to spend.

Remember looks are nowhere near as important as the compression numbers, and go shopping; and haggle.

Craig's List is a good place to find bikes too.

 

Well I have the XJ stripped down to the frame... and now that nothing else is on the bike, I can tell it really needs a good cleaning.

I decided since I can't stand going the summer without riding, to just buy another bike that runs so I don't rush anything on the rebuild. Picked up an 85 Virago today and think I will be happy with it. It isn't quite the style I like, but hey it is a bike that runs.

Now that I have something to ride, I think I am going to repaint the frame, and slowly start fixing the little imperfections on my XJ. I figure I have over a year before I need the XJ up and running so I can do everything exactly how I want it.