Barn Find - Cold Engine Compression #'s?

[ryamatt]

I'm new here and new to XS 650's. I am currently on a Harleys but I am looking to defect to the Japanese.

I am going to look at a sort-of barn-find tomorrow, a 76 xs650C. The owner said it hadn't been run for 2 or 3 years. I am hoping to get a nice deal on the start of a winter chop project.

It isn't currently running. If I can't warm it up, what kind of numbers should I be looking for on a compression test on a cold motor?

The buyer's guide I found here advised to walk away from a failed compression test and mentioned it would likely require a top end job worth around $300. That is within my budget and patience level, especially if poor compression means I can get the price down even lower.

Is a failed compression test worth the effort in restoring/repairing?

Thanks for helping a newbie.

Ryan

 

[deadchef]

I'm new here and new to XS 650's. I am currently on a Harleys but I am looking to defect to the Japanese.

I am going to look at a sort-of barn-find tomorrow, a 76 xs650C. The owner said it hadn't been run for 2 or 3 years. I am hoping to get a nice deal on the start of a winter chop project.

It isn't currently running. If I can't warm it up, what kind of numbers should I be looking for on a compression test on a cold motor?

The buyer's guide I found here advised to walk away from a failed compression test and mentioned it would likely require a top end job worth around $300. That is within my budget and patience level, especially if poor compression means I can get the price down even lower.

Is a failed compression test worth the effort in restoring/repairing?

Thanks for helping a newbie.

Ryan

i think you kind of answered the question yourself. you basically need to figure out the balance of what you're willing to pay vs. patience vs. what you're willing to take on.

titles certainly make the bike worth more although i have no idea how to get a bike street legal in canada. although even if it doesn't have a title and everything is in generally decent shape and you can get it cheap enough you could always use it for parts. you should atleast have the vin # run to make sure it's not stolen though...

 

[XSLeo]

On a cold engine that hasn't been run in a few years, it can be as low as 100 psi as long as it is even. Take some oil in a squirt can along. For a wet compression test. It will read higher and more like it will after you get it running. Often after a few hundred miles of riding the compression comes up.
If one side is very low look for sticking valves.
Yes, if low try to get the price down.
Doing a top end on the XS650 is not hard to do, these engines are fairly simple. The cam rides in 4 ball bearings, the rod big ends are roller bearings, the crank rides in three roller and one ball bearing.
A very strong lower end.
If you do get it and the compression is low check the piston to cylinder wear. If in spec a set of rings and lap the valves and new seals and gaskets and it should run fine.
Leo

 

[ryamatt]

i think you kind of answered the question yourself. you basically need to figure out the balance of what you're willing to pay vs. patience vs. what you're willing to take on.

I guess what I mean is: would a crappy compression test = totally don't bother, not worth the time or effort.

I know anything can be restored or fixed if you have the money and time. I guess I am trying to say that I would like a relatively straight forward winter chop project that can cost me a bit of dough, but not thousands. Is a failed compression test a bigger project than those basic conditions?

I know this is an annoying newbie post and there are a million variables....just hunting for advice.

R

 

[deadchef]

I guess what I mean is: would a crappy compression test = totally don't bother, not worth the time or effort.

I know anything can be restored or fixed if you have the money and time. I guess I am trying to say that I would like a relatively straight forward winter chop project that can cost me a bit of dough, but not thousands. Is a failed compression test a bigger project than those basic conditions?

I know this is an annoying newbie post and there are a million variables....just hunting for advice.

R

if it was me and i was looking for a winter build project, a crappy compression test (<100psi) wouldn't throw me off as long as: 1. overall condition of bike is ok, 2. there was a title and, 3. the cost was in the ballpark ($200-$500 depending on the rest of the bike)

hope that helps.

 

[ryamatt]

Thanks for this. I am going to look at it tomorrow so I'll let you know how it turns out.
R

 

[weekendrider]

You are going to want increased displacement anyway so......
poor compression may be the ticket/reason.

 

[gggGary]

When doing barn bikes I just kick em over and do a leg feel compression test. You can feel if you have both sides and enough pop so it will run. Much beyond that is kinda over the top on a non runner barn bike. I have put over 600 miles on a bike that that had zero compression on one side when I bought it, and I have not had the top off, it pulled 140 on that side a while ago, I should check it again. It is using a little oil but not enough to smoke. And I have run it hard, did 180 miles on the back roads one day running with an 1800 wingnut who likes to go. Well he could walk away from me at anytime but I sure TRIED to keep up.
It's kind of a win lose deal too, if you test it and it has good compression the seller's gonna start thinking hey it's a pretty good bike..... Stuck bikes are another matter. THAT almost always means a big project.

 

[resto]

Thanks for this. I am going to look at it tomorrow so I'll let you know how it turns out.
R

Ryan,

PM me. I can go and have a look at it with you if you like. I'm also in Winnipeg and have a 77.

resto

 

[ryamatt]

Ryan,

PM me. I can go and have a look at it with you if you like. I'm also in Winnipeg and have a 77.

resto

I didn't see this until now - I'm leaving in a few minutes to go see it. I'll let you know though, and maybe we can hang out and stare at bikes sometime.

I bought a compression test kit so we'll see. Looking at the posted pix, It looks like there is a leak at the head gasket and one of the fork seals is screwed up looking.

This isn't really bothering me. I'm hoping to use this as a chance to talk him down on the price. I spent all day yesterday looking at carb overhauls and top-end posts and videos. I was hoping to have a greasy winter season anyway...

We'll see. Thanks for everyone's input.

R

 

[ryamatt]

It looked pretty good, so I went for it.

I got what I think is a good price.

Compression was good - 95 on both cylinders. I think that is in the acceptable range given that it hasn't ran for several years and was cold.

No leaks, just filthy, and as I suspected, most of the rubber/plastic parts are in poor condition but the frame, engine, and forks look good. No mods or make-shift repairs.

Thanks for your input - you'll be hearing from me regularly I suspect...

Ryan

 

[gggGary]

 

[ryamatt]

Ha! Message received.

I'll put some up tomorrow after I bring it home.

R

 

[gggGary]

Just an anecdote about barn find compression tests. I grabbed a 5000 mile no title 79 barn find that last ran in about 1981. I was a dry barn, the engine kicked over with one obvious low compression cylinder. Tested 60 120 cold, came up to 130 both sides with PB blaster and then oil squirted in both sides. (Careful when doing this, kick it through vigorously a bunch with the plugs out before doing a compression test. You don't want to hydrolock the engine.)
I cleaned it, changed oil and filters, put a Pamco in, did a head stud re-torque, and bolted it into my 79 restomod, it fired up and ran immediately so I put on 100 miles. Compression is now 142-145 with no smoke! I suspect it will gain a bit more in the next few hundred miles of running.
Low compression in a barn find is more normal than not, one valve has been sitting open for a LONG time, rings get stuck in their lands, bit of rust on the bores. IMHO it's nearly always worth a try to run em a bit, a see what happens.

 

[Tomterrific]

Happened that way on my twenty year sitter. Got it running on low compression with an oil squirt in the plug hole and in the carb mouth. Every time I'd kick her I could feel the compression coming up.

Important for old engines that sit to squirt some oil inside. The main reason is to lube the dry valve stem so a valve won't stick open at first start or even first kick! This can take out a potentially good engine so remember to tell your friends.

Tom

 

[angus67]

(Careful when doing this, kick it through vigorously a bunch with the plugs out before doing a compression test. You don't want to hydrolock the engine.)
jeez, gggary, how much oil you put in there? my thought is you only need maybe 3 quirts(oil can) wait for oil to seep around, and kick away.
I bout a 50$ basket case with good title, one piston pin had let go of the piston, collapsing the piston and tearing it to shreds .I don't know what the guy was doing when it did this, but I had never rebuilt a engine before(except a b&s lawn mower),
and after a case of brake cleaner, and new 6th over kit, I really enjoyed rebuilding my motor.
I think 6 over equates to 680cc's, and compared to my buddy's stock 650, mine is a rocket, and im running a 17 sprocket. my comprosion after the rebuild was 150 psi. irrelevant to what you need to see, I just like to brag. 8)

 

[weaselbeak]

I don't worry too much about compression numbers on a motor that's been sitting. If the feedback from the kick lever seems ok, the numbers will go nowhere but up with a little lube and some run time. I find the odometer, if undisturbed, to be a pretty good indicator. Unless the oil is filthy, 30K doesn't scare me on this motor one bit. BTW, my son and I just put a bore and head job on his, and I believe it came in under 300 bucks for everything.

 

[gggGary]

you only need maybe 3 quirts

3 quirts would send one of our horses to the next county!

Yes I like to see lots of kicking over and valve lube before a start is attempted.
It's part of the reason I do that first compression test long as I am doing no start engine spinning anyways it's nice to get a base line and even better to see it come up after some running.
I have seen several disasters reported here from start ups with a sticking valve and bought a bike with a destroyed engine, probably from a stuck valve.

Agreed; hydro locking is more common from a leaking carb than too much oil, but no telling how much 3 squirts might be from some random oil can. Add in some PB blaster and gas from a leaking carb......
One recent XS I looked at had a cylinder full of "something" Came up on one side and then it was too much to kick through. I stopped at that point but no telling what damage some determined big guy could do.
The old KZ1300 inline 6s were kind of prone to a bent rod in the pot closest to the kickstand. Hydrolocking was the likely culprit as gas from leaking carbs tends to collect there.