Compression Test Tells Much

[Arclight88]

I performed a dry/wet compression test. Here are the PSI measures:

Left | Right
---------------------
Dry | 105 | 100
---------------------
Wet | 155 | 155

The wet test was performed by adding about 3-Tablespoons of motor oil into the spark plug holes just prior to connecting the compression tester.

Based on other threads and some research, the rings are bad and need to be replaced. Of course, other things may need to be done as well, but I am hopeful that this means that the valves are OK and may not require replacement.

 

[lhaolpa]

Bad rings sealed by the oil[temporarily]raised to higher reading.Could be stuck,broken,or just worn out.If it's been sitting for a while[years],it's possible that ATF will help clean and loosen up the rings and return it to service.If it's something other than stuck rings,then you'll need to re-ring at the very least. lha

 

[HoughMade]

Yep, I say do what you can to clean the pistons in place (ATF soak, seafoam, etc), get it running as well as you can (it will run on 105 psi....surprisingly well, though a bit down on power), then take measurements again. Personally, I'm not doing a ring job unless I know it os absolutely necessary.

 

[Arclight88]

Yep, I say do what you can to clean the pistons in place (ATF soak, seafoam, etc), get it running as well as you can (it will run on 105 psi....surprisingly well, though a bit down on power), then take measurements again. Personally, I'm not doing a ring job unless I know it os absolutely necessary.

OK, I will the motor an ATF soak.

By the way, I cannot get the motor to start now. Those of you following the other post concerning the 'slow turning starter' thread may have some insight as well.

Keep in mind, this motorcycle was running. It has the factory intake, exhaust, carbs, and pretty much everything else. I have not adjusted the carbs, the fuel was new on 12/1, and all of the fuses are good.

In other words, it started and ran prior to the compression test, and now it will not.

And by the way, Netiquette watchers, does this mean that I need to start a new thread since I have strayed off topic form 'Compression Test' to 'It Just Won't F*ing Start After the Compression Test'?

 

[drewpy]

And by the way, Netiquette watchers, does this mean that I need to start a new thread since I have strayed off topic form 'Compression Test' to 'It Just Won't F*ing Start After the Compression Test'?

your thread mate, do what you want with it

I think you need to get the motor running and get it warmed up good and proper, the sparkies will be fouled with the oil methinks

 

[Arclight88]

your thread mate, do what you want with it

I think you need to get the motor running and get it warmed up good and proper, the sparkies will be fouled with the oil methinks

OK, Drewpy, thanks. By the way, great execution on your vision with Speed Sh1t!

 

[drewpy]

OK, Drewpy, thanks. By the way, great execution on your vision with Speed Sh1t!

thanks ArcL

 

[bcware]

3 tablespoons is enough to muck up the plugs; it can also shoot out the intake and exhaust ports into the carbs and headers, respectively. Ideally I don't think it should drip into the intake side, but during testing and a tear-down I found evidence despite finding nothing wrong with the valves. Most of it, however, is going to get blown into the headers.

 

[lhaolpa]

It should be obvious that to affect the pistons and rings,the pistons should be below the combustion chamber,with one piston between the tdc,descending,the other between bdc,ascending.In this position,the one ounce of ATF will work into the rings and be gone overnight even if the rings are in decent shape[remember,there are gaps in the rings]. When left overnight,the plugs shouldn't have any oil on them,and there shouldn't be any left to foul valves,carbs or even headers.I've done this many times on many types of motors including outboard motors,Volkswagen horizontal motors,motorcycles,tractors,lawnmowers,etc. I've never experienced any bad effects from this method of cleaning the rings.If you have any fear of something bad happening,simply don't use this method and dig into the motor first. lha

 

[bochnak]

Do a leak down test to pinpoint where the leak is and how bad:

How to make:

How to test:

BTW, your not using a HF comp tester are you?

 

[Arclight88]

Do a leak down test to pinpoint where the leak is and how bad:

How to make:

How to test:

BTW, your not using a HF comp tester are you?

No, I am not using a HF (Harbor Freight) comp tester.

I added about 3-Tablespoons of ATF to both cylinders on 12/3/11. On 12/5/11, I attempted to start the motor with no success.

At this point, I removed spark plugs, set motor to left TDC, and held the rubber tipped air gun to the left cylinder as I held the motor at TDC via a wrench. It was all I could do to keep the engine at TDC, but I did not observe air escaping from the engine. There was some minor hissing at the oil port on the crankcase.

I then turned the engine such that the exhaust port was opened, and I could hear loud air noises from the left exhaust pipe - as expected. I then turned the motor such that the intake valve was opened and I could hear loud air noise in the left carb and intake manifold.

I stopped there, and decided that since I was not 'losing' a lot of air via the rings, to perform on the left side, to try another comp test.

Dry test was performed with results of Left: 105 PSI Right: 115 PSI.

I then re-installed the plugs, set things to start, and hit the button. The motor started on the second turn, ran OK for 8 seconds, and died. I have not been able to get it restarted since then. I have tried several settings of choke ('enricher'), petcock steeings, and throttle. Still no start.

Documentation says standard compression rating for this engine is 150-175 PSI per cylinder and only 15% below minimum is permitted (127.5 PSI).

I am considering the following plan of action...Firstly, clean the carbs and see if that gets it running and, Secondly, replacing the rings, wether it does or not since it is not even close to operational minimums for the design.

Any thoughts or advice would be most welcome.

Thanks all...DJ

 

[Arclight88]

No, I am not using a HF (Harbor Freight) comp tester.

I added about 3-Tablespoons of ATF to both cylinders on 12/3/11. On 12/5/11, I attempted to start the motor with no success.

At this point, I removed spark plugs, set motor to left TDC, and held the rubber tipped air gun to the left cylinder as I held the motor at TDC via a wrench. It was all I could do to keep the engine at TDC, but I did not observe air escaping from the engine. There was some minor hissing at the oil port on the crankcase.

I then turned the engine such that the exhaust port was opened, and I could hear loud air noises from the left exhaust pipe - as expected. I then turned the motor such that the intake valve was opened and I could hear loud air noise in the left carb and intake manifold.

I stopped there, and decided that since I was not 'losing' a lot of air via the rings, to perform on the left side, to try another comp test.

Dry test was performed with results of Left: 105 PSI Right: 115 PSI.

I then re-installed the plugs, set things to start, and hit the button. The motor started on the second turn, ran OK for 8 seconds, and died. I have not been able to get it restarted since then. I have tried several settings of choke ('enricher'), petcock steeings, and throttle. Still no start.

Documentation says standard compression rating for this engine is 150-175 PSI per cylinder and only 15% below minimum is permitted (127.5 PSI).

I am considering the following plan of action...Firstly, clean the carbs and see if that gets it running and, Secondly, replacing the rings, wether it does or not since it is not even close to operational minimums for the design.

Any thoughts or advice would be most welcome.

Thanks all...DJ

Have completed a carb removal and cleaning with following issues:

The manual says float height should be 32mm +/- 1mm above the bowl flange. My readings were L: 26.27mm and R: 25.55mm. So the float heights were almost 1/4 of an inch out of standard. I adjusted the tangs to get the floats back to 32mm. I wound up with L: 31.76mm and R: 31.88mm.

I cleaned the jets, carb bodies, float bowls and passages with carb cleaner and compressed air. All in all, the carbs appeared to be in good shape. Very little crud appeared - which is consistent the PO's carb servicing back June '07.

Reconnected the vac line to the barb on the right carb spigot, replaced the tank, connected the gas line, reconnected the carbs, manifold, and air cleaners.

Primed the carbs, plenty of gas in both bowls. Set the enricher, kicked it over, and it sputtered to life for 3 seconds.

Since then, nothing. I have tried various settings of enricher, throttle, and petcock settings, but the bik refuses to start. Verified spark is working on both sparks (I have not replaced the sparks yet, but I could!)

A wise man once told me that internal combustion motors need fuel, air, spark to run. I have verified that all of these are pressent at the combustion chamber, but it will not start or run. It is possible that the timing got messed up, but I do not know how this would be possible, since prior to the first leakdown test, this was a running machine.

I think I need to move on to the compression as the culrpit.

Thoughts and suggestions are most welcome...DJ

 

[lhaolpa]

I would think that the motor should start and run,albeit weakly,at the compression values given.That being said,it may not start easily.new plugs,or cleaned up ones should help.There may be other problems keeping it from starting.When running for a short time,did the plugs become oil-fouled?Air escaping during your test indicates that the rings are not sealing to a great degree.That would create a lot of blow-by and cause problems such as oil-fouling of the plugs.I've seen motors on cars,trucks,etc. run for years,though not well, at low compression levels,but the more cylinders would allow them to run when this condition exists. All things considered,this may be a good winter project,reworking the top-end.Good luck. lha

 

[bochnak]

Verify correct point gap and timing.

Double check that float height. I recall reading here that typos occur in some manuals. Mine were set in the 25 mm range, which gave me a fuel height 2mm below the parting line.

 

[Arclight88]

Verify correct point gap and timing.

Double check that float height. I recall reading here that typos occur in some manuals. Mine were set in the 25 mm range, which gave me a fuel height 2mm below the parting line.

So I had the day off, and since I am now armed with the truly important information that the float bowl gas level should be 2mm less than the carb flange bottom. I decided to test my settings again.

I bought some clear plastic tubing and attached a section of it to each float bowl drain nipple and stretched the hoses upward toward the gas tank. I then loosened the float bowl drain plugs and set the petcock to prime. I then measured the height the fuel in the tube relative to the carb flange bottom. After carefully setting the float heights to 32mm +/- 1mm the left carb fuel level was 13.57mm below the flange top and the right carb measurement for 8.97mm below.

Something was clearly wrong.

I changed the float settings to 25mm, remeasured and got L: 4.31mm and R: 2.06mm.

I am convinced that I can readjust the left carb float level close to 2mm. By the way, the bike still won't start, but I have not checked the points or changed the plugs.

I intend to focus on things that I can accomplish, get after the top end, paint the thing, and then once it is all done, get it running.

 

[bochnak]

FWIW, mine was running on the LH cyl only. I discovered that the point gap was waaaay too big, and as a result the timing was off. After setting the points and tiiming, the bike fired on both cylinders.

Also, it would be easy to check the valve adj and make sure you some clearance, even though most of your leak is past the rings.

I would at least attempt to try and get it running, then seafoam the engine to see if carbon/varnish on rings are causing your issue.

 

[drewpy]

good point Bo,

if you change your spark gap, you need to re-time the engine's ignition!

its important to have both gapped exactly, that's where dwell meters come in.
So long as they have the both dwell settings and are near as damit to the gap specs, the timing on both cyls will be ok

 

[bochnak]

BTW, I checked my fuel height last night since I had to solder some holes in the floats. The fuel level was even with the top of the float bowl screw head.

 

[Arclight88]

Alright! I reset the float heights again. Left bowl fills to 0.5mm below flange base Right is 0.76mm. The engine did not start. So I changed the spark plugs, kicked it over, and it started right up! Runs great.

So I have a bike that runs, and pretty well at that, yet still has compression of only 90PSI. So I think I will pull the head, change the rings, gaskets, etc, and see if the compression comes back up to standards.

But I appreciate all the great advice and encouragement on getting the machine running again!

 

[bcware]

Research the costs involved. From what I have seen it is much, much cheaper to simply buy a new engine. Assuming there are no other problems you're looking at $300 or so in parts plus shipping and the cost of a re-bore.