When does a bike with low compression become a parts bike

[Mikey]

I have been struggling with my 73 for months now and just for the hell of it I borrowed a compression tester from a local auto parts store
Dry Right cyl 92 psi left 89
Wet Right cy 117 left 119
When I did the test I didn't know you need to have the throttle wide open
So the dry test might be skewed because I didn't have the throttle wide open but the wet test did have the throttle wide open
And the shop manual said just give it 5 or 6 kicks On both test I used the electric start on the right side and of course having the decompression lever there on the left I had to kick the shit out of it until the needle stopped rising
Parts bike?

 

[JesseeS]

I wouldn't say a parts bike. If everything else is good I'd say good time to go big bore, but either way a new top end.

 

[Mikey]

As a novice (at best ) I wouldn't want get that deep into it
I noticed when doing the test that while doing it I would leave the tester on for 5-10 minutes and there was no real bleed down
As in it maybe lost 1 psi

 

[Mailman]

It surprising just how well a bike with low compression can still run. Our old friend Robin C. had a bike he used to ride daily that had low compression, that bike was the easiest starting bike , he even made a video of him kick starting it by hand! He eventually did a top end on it, but it was running just fine the way it was.
Another old member, Daniel Black used to have a really good running ‘77 that had low compression, I rode his bike and honestly it didn’t feel any different from mine.
I’d say keep riding it or sell it as a whole, but I wouldn’t break it up. If it were me.

 

[Mikey]

Yeah it does kick easy
I wouldn't want to part it out maybe some one will want the challenge just not me
Selling it on CL or wherever would be a pain weeding out the knuckle heads from normal people
And trying to sell it on FB no way most of those people have no concept of call or text

 

[RustiePyles]

Did you adjust the cam chain and valves before you did a compression check? Poorly adjusted valves will cause low compression. A normal compression tester has a schrader valve in the end of it it will not show leak down. You need a leak down tester for that, is uses compressed air.

 

[grizld1]

You wouldn't see pressure loss on the compression gauge. That valve that you release to zero the gauge ensures that only the highest pressure reached is indicated. You might want to find out what's causing the pressure loss. New pistons, rings, and bore job can be a bit costly, but lapping the valves is cheap and easy. A leak down test will tell you where pressure is being lost. There are several threads giving procedures, seek and you will find.

I'm not trying to be patronizing, but if you had to borrow a compression gauge, that tells me that old motorcycles may not be for you. They take time, patience, tools, and willingness and ability to spend money. There's no shame in not wanting to get into all that. I've sold a couple of bikes on CL and had no trouble at all. Good luck with the sale.

 

[Mikey]

You would think that the pressure would blead down but I wouldn't know much about it
And yes this motorcycle for sure doesn't need me more and the good honest truth from someone is always welcome
And even running I would have to tell the next person about the low compression issue
Parts bike it is

 

[Mikey]

Did you adjust the cam chain and valves before you did a compression check? Poorly adjusted valves will cause low compression. A normal compression tester has a schrader valve in the end of it it will not show leak down. You need a leak down tester for that, is uses compressed air.

Well I did adjust the cam chain and I sure that was ok
But setting the valves I checked them over and over again each time revolving the engine a few times so they should be right but like I've said a mechanic I'm not
I may have to give it one more try on checking the valves again

 

[RustiePyles]

Well I did adjust the cam chain and I sure that was ok
But setting the valves I checked them over and over again each time revolving the engine a few times so they should be right but like I've said a mechanic I'm not
I may have to give it one more try on checking the valves again

Tight valve adjusters will cause overlap, thats when the exhaust valves and intake valves are open at the same time for a period of rotation. This is normal but the tighter the adjusters the more overlap you have, the more overlap you have the less compression you have. To get a more accurate indication of actual compression you need to increase the rocker/valve gap on the exhaust valves to the point where you have zero overlap. I wouldn't do this unless I had real good reason, but its a handy trick.

 

[mike in idaho]

You might want to remove the carbs and do another test, or at least prop the slides up with a popsicle stick or a strip of cardboard to make sure they open. Slightly lower numbers at cranking speeds don't mean the rings aren't sealing well when it's running. Cranking it over, you are relying on ring tension only to hold the rings against the cylinder walls. When it's running there is a lot of gas pressure behind the rings, forcing them out against the cylinder walls, hence a lot better seal. To look at it another way, if the rings actually leaked as much when running as they appear to do at cranking speed, there would be a WHOLE LOT of wind coming out the crankcase breather, oil would be leaking at the seams and blowing seals from the pressure inside. Too bad there isn't a way to measure dynamic compression, while it's running, like we used to do with those automotive tune up machines from days gone by.

 

[jetmechmarty]

I agree with above. Adjust the valves. No good? Pull the engine. I might be fixed with a valve job, cylinder honing, and rings. It's all no big deal for much of the population of this forum. To the general public, it's probably a goner. Even people with mechanical inclination have no idea about the stuff that makes these bikes tick.

 

[willis]

If nothing else Mikey, this might be a good learning opportunity for you. Take a crack at opening that motor up. It really is surprising at how simple these motors really are. What's the worst that can happen, you find you aren't up to the task and it turns into a parts bike anyhow? You now have a few bikes, so spare parts are not a bad thing to have around.

 

[ckahleer]

I have had bikes with compression nunbers like that and they ran OK. I certainly would not decommision a bike for low compression. Either live with it or have the top end work done. Before making a dicission on the bike, I would do another compression test. Engine warm, Throttle open, and decompresion mechinisum disabled.

 

[Mikey]

If nothing else Mikey, this might be a good learning opportunity for you. Take a crack at opening that motor up. It really is surprising at how simple these motors really are. What's the worst that can happen, you find you aren't up to the task and it turns into a parts bike anyhow? You now have a few bikes, so spare parts are not a bad thing to have around.

Yor right no matter what I do it will always be a parts bike at worst

I have had bikes with compression nunbers like that and they ran OK. I certainly would not decommision a bike for low compression. Either live with it or have the top end work done. Before making a dicission on the bike, I would do another compression test. Engine warm, Throttle open, and decompresion mechinisum disabled.

Yaeh I never though about just disconnecting the decompression lever at the engine
It's easy enough to do
As always thanks guys !

 

[Mikey]

I also got a bunch of parts for a 77 a while ago basically everything except the rolling frame and engine
And I still have all those cool tools that I've been buying
It will have to wait awhile springs here gardens 1st riding bikes 2nd but it does rain here

 

[grizld1]

If it's all or mostly there, numbers match, and paperwork is good, your TX isn't a parts bike. It may take time to find the right buyer, but the TX650 is a pretty machine, and if yours isn't a complete rust bucket you'll get decent money from somebody looking for a bike to refurbish or restore.

 

[mike in idaho]

If it starts and idles decently and doesn't use oil there's not a lot to be gaining by tearing it apart.

 

[Jim]

If it's all or mostly there, numbers match, and paperwork is good, your TX isn't a parts bike. It may take time to find the right buyer, but the TX650 is a pretty machine, and if yours isn't a complete rust bucket you'll get decent money from somebody looking for a bike to refurbish or restore.

Absolutely. Even a diamond in the rough is still a diamond. If you have matching numbers and papers, it's far from a parts bike.
120ish isn't great, but it ain't bad either.
If it sat forever before you picked it up Mikey, there's a better than even chance it'll improve after a few hundred miles.

 

[Jan_P]

Yes as others have stated
Mike in Idaho fex
I had one with " Soft " kickstarting but it ran well and did not smoke ..
I don't know of US condition but here it has been so in the ca 30 years I followed the prices in the last owner segment.
That a complete starting bike had a rock bottom price typically $ 1000 -- 1200
If it had a MOT it was a bit higher and if it looked awful a bit lower

If it was the same bike in a box in parts half of that or less depending on wear and bike but a typical Triumph
10 -15 - 20 years old did not matter the same rule Last owner segment $ 1000 -- 1200

The second question people asked was if it had been " sönderskruvad "
that is if some hack had tried to work on it over tightening every bolt on the motorcycle damaging half of them
with a pipe wrench at his full strength or other incompetence. Untouched cost more.

Then there is the aspect on how much will it run I have seen early models smoking and rattle..Looking mint on the exterior But if you only ride to the Highway cafe . 3 - 5 times a season it works for that owner .
Other can look like scrap on the outside but run perfect for a more active rider .who puts his effort on the mechanical rather than Polishing.

So no dismantling .. for parts the saying
" There is no normal wear on an enthusiast vehicle they only get better over the years "
So a bit soft compression is nothing to worry about
" You don't need to worry about these problems so much right now ...there will be new ones pretty soon "

As Mike in # 18

If it starts and idles decently and doesn't use oil there's not a lot to be gaining by tearing it apart