Compression Tester

[Muley]

I have been shopping for a compression tester and found quite a few available anywhere from reasonably priced to the "sky's the limit". Can anyone recommend a particular brand and/or model that is easy to use, relatively accurate and won't cost three figures ?

 

[Christofero]

IMO really any cheapola compression tester will do ... the important thing is to do the test properly and interpret the results correctly.

1. Open the throttle fully.
2. Use a fully charged battery and warm engine.
3. Spin the engine for no more than 5 seconds.

Understand that the number will be an approximate number - if both cylinders are more or less the same and some value above 140 probably everything is OK. An expensive compression tester will not necessarily get you a huge increase in accuracy.

You can calibrate the gauge using shop air. One thing about gauges is the cheapest ones mount the bourdon tube directly to the back of the housing - tweak/wrench the housing and the gauge goes out of whack. The good ones have a separate solid mount for the tube.

A much better thing is to get a cylinder leakage tester - again a cheap one is fine. I bought one from Princess Auto which seems to work fine - it cost $60 CDN. THe nice thing about a cylinder leakage tester is you can pinpoint the exact problem in seconds by just listening where the hiss is coming from. Most guzzi's will be in the 5% range.

It is also not a bad thing to get a rotameter and measure the engine's blowby. This is just another way of assessing how the rings are working.

ChrisR

 

[Muley]

Christopher, 'preciate the info. I picked up an inexpensive compression tester at NAPA yesterday that looks to be well-made. It has screw-in fittings rather than the universal rubber cone attachment. I read somewhere that you could squirt a little oil into the plug hole after the first reading and check it again. If the compression is still low the second time then the valves or seats would be suspect rather than the rings. Does that sound logical ?

 

[WayneOrwig]

You can do that, but a leakdown tester is so much better IMHO. Particularly for tracking a problem.

 

[Christofero]

That is called a 'wet test' and yes it works - the oil makes a temporary hydraulic seal.

The rubber bung type compression testers are pretty much junk - it is almost impossible to get a good seal.

A cylinder leakage test is the best thing - even just pressurizing the cylinder with a fitting brazed onto a coupling can tell you pretty much what you need to know. Some companies make a big deal about the two gauge (differential) type versus the single gauge versions - I don't see that there is a big difference. Just make sure that the engine is on TDC and be careful not to leave the bike in gear - the engine can suddenly turn over and cause injury if your body is in the way.

 

[Muley]

Thanks for all the advice everyone. I plan to do both the compression and leakdown tests ASAP. With my closest dealer 100 miles away, it makes sense for me to DIY everything, within my ability anyway, rather than pay shop time and the expense of riding to and from the dealer. I would think the shop charges alone would cost as much as the test equipment.

Right now, I suspect bad exhaust valves and/or seats. After I get the results, I'll post them so some of you can comment on what the next step should be. If bad valves, then it would probably take a while for the shop to order the parts, and there's no need for my bike to be sitting somewhere for a week or so.

BTW, is it a good idea to do a compression check on any higher mileage vehicle one is considering purchasing? It seems like a good initial check of things, that is, if the seller didn't mind.






PS It's a good thing Wayne lives even further from me than the nearest Guzzi shop or I might compete with Bill H. for his "shop time"

 

[WayneOrwig]

You can borrow my leak down tester.

No point in buying one since they get used so seldom.

You need an air compressor though.

 

[Muley]

A moment of silence please

I ran a compression check this evening on my EV and had good news and bad news. The good news was that the left cylinder showed an average of about 142 psi. The right side averaged only 65:unsure:

On the first few runs measuring the left cylinder, I forgot to open the throttle and got readings significantly lower averaging only about 92. Is this differential normal?

I first warmed up the engine to a point that removing plugs resulted in burnt fingers, so I suppose that was hot enough. Then I screwed in the gage just using my fingers (so it was not all that tight). Actually, I failed to see how a wrench would even fit in with the hose attached. I pulled out the fuel pump relay to prevent gas from going anywhere. Then I let the engine spin over for a few seconds with WOT and repeated the test about three times for each side. Just to be sure the gage was accurate, I forced compressed air into it, and it checked out perfectly.

I am expecting a leak down tester to arrive any day now, and I'll try to pinpoint where the problem is before heading to a shop for surgery.

Is the huge difference between sides typical ? I would expect wear and tear to be about the same from one side to another but logic says that one valve (or rings) could buy the farm first. BTW, the engine has about 111,000 miles now with nothing done to it that I'm aware of. Is that a decent life for a Guzzi motor before needing major work? With the low compression on one side, it's probably been running, more or less, on one cylinder while the other one just "goes along for the ride".

Now I know why my fuel economy has gone south and so has power.

I am looking forward to getting the engine back to spec. and doing some serious riding again

 

[ed]

Minimum, you need a valve job.....at 110k, it's time. Probably need rings, too while you're in there.

Ed

 

[Muley]

Doc Ed surmised:

Minimum, you need a valve job.....at 110k, it's time. Probably need rings, too while you're in there.

I suppose the bike is due. It's never let me down (or at least made me walk), although there was a time that I seriously thought of rolling it off a cliff and flying home, but that's another story.:angry:

Any particular valves and/or seats recommended or will Guzzi OEM do the trick? I am looking forward to having it finally run like it should for a change. Surprisingly, I see zero smoke, it uses almost no oil, and the only leaks are a slight weeping around the temp. sensor and maybe a tiny amount on top of the engine. It starts just fine, idles smoothly, and actually sounds pretty good, just a noticeable lack of power and a ceiling of about 35 mpg.

I'll see if I can track down the main culprit(with leakdown) just for fun and since I've never done it before. Then - a trip to the hospital

Can the parts be gotten from Guzzitech?

 

[Muley]

Guzzimoto suggested (in another thread):

you can take advantage of the opportunity and have the ports done. The stock job is pretty so-so. Think of the power you could have!!!!!

Is cylinder head porting a good idea on a highway only Guzzi ? It appears that I'll have everything apart real soon and can have this done if it's a real benefit with no downside other than cost. Any other opinions on porting ?

 

[GuzziMoto]

I know you want OTHER opinions and not so much mine again, but as long as the guy doing the porting understands it is a street bike and knows what he is doing there is NO reason not to have the ports cleaned up. As long as he doesn't hog out the ports there is no down side to free horsepower. The only downside is that if he does not know what he is doing he can screw up the street manners with ports that work at high rpm (on a Guzzi?) and fall on their faces at normal street rpms.

 

[Muley]

Thanks for any and all input, as this is a learning curve for me. As for the porting, I had to send a link to the shop rep. (where I intend to take the bike) that explained what porting was :dry: He contracts out engine work, thank goodness, since he was not familiar with the procedure at all. I assume that what GuzziMoto means is simply smoothing out and mildly shaping the existing intake path and not going to the extreme of milling a new one. My limited understanding is that factory work leaves burrs and other imperfections that can interfere with proper airflow. If this is totally off base then someone please straighten me out. The whole idea seems to be perfectly logical to me.

Now, can anyone give me a ballpark estimate as to what a ring and valve job should cost so I'll have some info. to work with when dealing with the shop ?

 

[Penis Rotor]

Sounds like you've got a burnt valve if the compresion test has been done correctly. On a hot motor I'd be expecting a minimum of 165-170PSI per side.

You have to have the throttle plates open to get an accurate reading. If there is a gale blowing in your front door and you shut the door so the wind can only get in through the cracks in the door jamb not as much wind gets in, right? Same with the venturi of a carb or the plates of a TB.

As long as you've checked the valve clearances and made sure that one of the valves isn't being held off its seat I wouldn't bother with a leak down test. Top end's going to have to come apart anyway.

Paying big money to have the heads of a road going Cali ported is, IMHO a silly waste of time. Match up the ports to the manifolds with a dremmel or die grinder and leave it at that. You'll notice very little difference in performance and remember, if you increase the amount of air going in you'll have to increase the amount of fuel to maintain the SR. If you get a big enough flow gain you'll need a map modifier of some sort. why bother???

Pete

 

[Muley]

Thanks Pete and everyone else. I'll get this project started ASAP and report back when everything is back together.

 

[GuzziMoto]

Muley wrote:

I assume that what GuzziMoto means is simply smoothing out and mildly shaping the existing intake path and not going to the extreme of milling a new one. My limited understanding is that factory work leaves burrs and other imperfections that can interfere with proper airflow. If this is totally off base then someone please straighten me out. The whole idea seems to be perfectly logical to me.

Yes that is pretty accurate. It is true that if you go to far with the porting you will have to change the fueling. But the notion that cleaning up the ports and improving the the stock production job is a waste of time on a Cali (or any other Guzzi) is a waste of time is not an opinion I share. Making any bike do its job better is never a waste of time to me, and if you're doing a top end anyway it is not much more to clean up the ports and match things up. Matching the valve seats to the ports, smoothing any sharp edges and removing burrs, and matching the manifolds to the ports are the key points. To me it would be silly not to.

 

[Muley]

I finally got around to doing the leak down test this afternoon and would like to hear from anyone that can add to the following and tell me if my diagnosis is on target or pure BS:

First, I set out to properly adjust the valves, even though it's been only 2500 miles since the last time. I know that this should be done with a cool engine as I have done each and every adjustment to my EV since I bought it. I guess it was a senior moment, but I walked out into the garage with the intent of doing the valves, wires in the cerebellum got crossed, and I cranked the bike to warm it up for the leak down test.:angry: As I was gathering tools, it dawned on me that I was running my bike, crap, I shut it off and fetched a giant workshop fan to cool the engine down so I could start again. I learned that air cooled motors can warm up very quickly, and it took at least 30-45 minutes before I could start the valve adjustment.

Ok, now that the engine's "room" temperature, I went about my normal valve adjustment procedure and found that both exhaust valves were super tight and had to be loosened just to get the .006 gage in the gap. Both intake valves, on the other hand, had to be tightened up slightly, and they were set to .004. This has been the rule for the past couple years now with the right exhaust valve clearance tightening up the most.


Once the valves were set on one side and the piston was at TDC, I hooked up the leak down tester to the compressor, set it at 100 psi and then connected it to the hose hanging out of the spark plug hole. It was then that I learned an air compressor makes a tremendous amount of noise:angry: , and there was no way I was going to be able to hear air leaking. So I spent the next 15 minutes moving the compressor out into the yard and dragging out extra air hose and extension cord. When I connected to the right cylinder nothing happened, as in 100 % leakdown. I could hear air whooshing from both exhaust pipes (I figured that was plausible since they are connected with a crossover), from the oil filler cap, and just a little behind the butterfly on the TB. I found it was easier to hear by using a two ft. length of PVC pipe and holding one end up to my ear while the other end went to each of the three major leakage suspects.

Then I did the valve adjustment on the left side and hooked up the leakdown unit to that spark plug hole. This time I got a reading of 27%, yippee, merely a "tired engine" on that side. Air was heard at the exhaust, oil filler plug and a little bit at the TB butterfly.

After exhaustive research on this subject, diligent reading of forum posts and other independent study I came to the conclusion that my engine is f$@&ed, to use a technical word.

Seriously, it sounds like bad rings and exhaust valves with less noticeable wear on the intakes. New valves, seats, springs ? and rings all around if you please.

So, she goes to the shop in about a week.

My question is this. Since the engine will be torn down anyway, is there anything else that should be checked/replaced will we're at it ? I want this done right and don't particularly want to go back into the mill anytime soon.

The bike starts up quickly, idles great after a little warm up, sounds good, and actually runs OK. How can that be with basically one sickly cylinder doing all the work? BTW, the exhaust pressure coming out of the pipes while it was running was greatly different from one side to the other. The "bad" right side had weak exhaust while the "good" left side felt stronger.

As always, comments, suggestions and any other responses are appreciated and welcome.

Russ

 

[Penis Rotor]

You set the piston at TDC but are you sure it didn't spin the crank when you started pushing air into it?

Pete

 

[Muley]

Pete asked:

You set the piston at TDC but are you sure it didn't spin the crank when you started pushing air into it?

Pete, it is so worn out that I don't believe 300 psi would move it.:laugh: The air hissing everywhere was amazing, but I know it didn't spin since I had it on the stand in 5th gear, and nothing moved. I had left it in gear intentionally thinking the piston needed a little resistance to being moved by the compressed air, but it wasn't necessary. It's incredible to me that the leakdown shows 100% on one side and the thing still runs. Even the "good" left side at 27% didn't budge the wheel. I think I know why it won't pull anymore in 5th:silly:


I also tapped on the rocker arms with a rubber mallet while the air was hooked up to see if the valves might not be seated, but there was no change at all.

 

[Penis Rotor]

OK, so it definitely sounds like it needs a top end freshen up. Odd though, I wouldn't normally expect any thing like that degree of degradation. something must of caused it.

Pete