Unfortunate results

[Jfl0528]

hey everyone,

A while back I had posted that I bought a 1977 xs sight unseen. I did not know if it ran or not, I just bought it. It was beat up. I ripped the engine out and started buying carbs, intakes, etc. I popped the right side spark plug out and stuck my thumb in the hole while I cranked it to feel compression. Felt fine. I assumed both sides were okay. I thought wrong. Turns out the left side has no compression. Literally zero.

I think that for the price of buying engine rebuild parts or big bore kits, it’s not worth keeping the bike.

Of all the experienced bike builders and riders on here, would you recommend that I spend money on rebuilding it? Or should I trash the idea altogether?

I think it would be a fun little project to make it EXACTLY how I want it. But I’m not certain dumping money into it would be a good idea.

I bought it for $300 this past September, and so far I have $250 into it.

What do we think? I need some guidance, all my friends say trash it.

 

[grouchie83]

Does the compression change if you drop oil down the spark plug hole? If it does then you might just need new rings.

 

[Jfl0528]

Does the compression change if you drop oil down the spark plug hole? If it does then you might just need new rings.

I sprayed a load of penetrating oil down there. Unchanged

 

[grouchie83]

I sprayed a load of penetrating oil down there. Unchanged

Did you pop the head off or throw a borescope down the spark plug hole to see if the piston has some non-factory ventilation?

 

[grouchie83]

I also have a 77 that I'm slowly working on, for what it's worth.

 

[Jfl0528]

Did you pop the head off or throw a borescope down the spark plug hole to see if the piston has some non-factory ventilation?

I did throw a boroscope down there, everything looked fine. Little carbon buildup but nothing crazy

 

[grouchie83]

Well... taking stuff apart and looking at it is free. I'm out of ideas. Maybe someone rebuilt the engine before and failed to put rings on the left side???

 

[Jan_P]

Anything known about mileage .. ?
I would look for a stuck valve possibly .. And not give up just yet.
I would expect some problems on a $ 300 motorcycle and work needed and cost
Since the bore scope inspection looked OK It can still be a good project if a low mileage machine.
Not done it myself but some compressed air ( low pressure ) in spark plug hole ... can hear where it leaks out.

 

[mike in idaho]

The purchase price is almost always the smallest item on the sheet, when you add up the cost of everything at the end of the project.

 

[Jfl0528]

Anything known about mileage .. ?
I would look for a stuck valve possibly .. And not give up just yet.
I would expect some problems on a $ 300 motorcycle and work needed and cost
Since the bore scope inspection looked OK It can still be a good project if a low mileage machine.
Not done it myself but some compressed air ( low pressure ) in spark plug hole ... can hear where it leaks out.

Odometer reads 9,955. I definitely am aware a $300 bike would have problems. My friends don’t seem to understand that, and we’re all mechanics, go figure. We do this for a living. I will try and blow some air in tomorrow, the engine is at my work

 

[Jfl0528]

The purchase price is almost always the smallest item on the sheet, when you add up the cost of everything at the end of the project.

100%! But their big argument is that I can buy a running bike for the cost of all the parts

 

[Jfl0528]

Well... taking stuff apart and looking at it is free. I'm out of ideas. Maybe someone rebuilt the engine before and failed to put rings on the left side???

Hey, ya never know!

 

[Jan_P]

10 000 miles is good ... It can be a Cylinder head valve job only. ( + rings ) And still have many years left to ride.
Lets see what you can find .. If you like you can post more pictures
getting an overall evaluation -- I would not care about exterior.
If you wont rebuild it someone else will at that odometer number.

 

[Jfl0528]

10 000 miles is good ... It can be a Cylinder head valve job only. ( + rings ) And still have many years left to ride.
Lets see what you can find .. If you like you can post more pictures
getting an overall evaluation -- I would not care about exterior.
If you wont rebuild it someone else will at that odometer number.

Thanks for the insight. I definitely think I’m gonna keep it now that I heard all these positive responses. I’ll bring it back home and break it down. I’ll probably end up buying a repair manual first and once that comes in I’ll dig in and send some pics

 

[ssjody]

Here's some advice @Jim gave me when I had a similar issue. My problem turned out to be bent valves but this would certainly be worth a try.

This is a procedure in the Lycoming Engines book. It's called "staking the valve." I've had good success with it on valves that are carboned up.

For the intake, move the piston down to BDC on the power stroke so there's no piston or cam interference. Take a solid piece of hardwood small enough to fit on the rocker arm, but big enough it won't splinter**. Set it on the rocker as squared up as you can eyeball and smack it. No time for love taps, hit it like you mean it. This causes the valve to pop open and slam shut on the seat.... breaking up any carbon/rust buildup on the valve and the seat. Repeat about a half dozen times and recheck the compression. If it improved a little, repeat as necessary until the valve closes on the seat like it's supposed to. If you can get compression up to about a hundred or so, run it and let the engine do the rest.

 

[bikefreak69]

I would certainly fix it if it were up to me. I have 2 XS 650's, one I did a budget rebuild on for about 800 bucks to get it into rideable shape and the other one is complete for parts but has major issues to get it running again (needs crank rebuilt). I have about 1800 in the rideable one and it is a hoot to ride. It had cam installed incorrectly when purchased, causing bent valve and broken valve guide therefore causing it to be parked in 1984 and never touched til I bought it with title for a whopping 75 bucks. With much elbow grease and a decent chunk of change thrown in, I had a running bike. So if you are mechanically inclined, you should have no problem.

 

[grouchie83]

Here's some advice @Jim gave me when I had a similar issue. My problem turned out to be bent valves but this would certainly be worth a try.

I was also thinking a valve stuck open somehow.

 

[Jim]

popped the right side spark plug out and stuck my thumb in the hole while I cranked it to feel compression. Felt fine. I assumed both sides were okay. I thought wrong. Turns out the left side has no compression. Literally zero.

If it sat for an extended time, there's a possibility one of the valves is stuck (rusted) open a smidge. Make the room as dark as you can, shine a light into the spark plug hole and look in the intake and exhaust ports. If you see light, the valve is stuck open.

 

[AUTOMAN]

Lots of ifs and buts but engine comes apart regardless of oil added or borescope or inspection through small holes.

$300 is a good start. Maybe suck it up.

 

[Jfl0528]

If it sat for an extended time, there's a possibility one of the valves is stuck (rusted) open a smidge. Make the room as dark as you can, shine a light into the spark plug hole and look in the intake and exhaust ports. If you see light, the valve is stuck open.

Good call I’ll try this tmrw