Another T rebuild: left cylinder compression

[Testarossa]

Longtime readers may remember that my T was submerged in the flood of September 2013 and I did an engine rebuild to clean the mud out of everything. Could never get it to run just right thereafter and finally realized that compression was low on the left cylinder. I thought it possible that I failed to get all the sand out of the left cylinder head and might have wrecked a piston ring and scored the Nikasil.

So . . . ski season over and a miserable rainy weekend so I popped off the left jug. Piston rings don't appear damaged and there's no evidence on the piston of blow by:




Some vertical marks on the cylinder wall but no irregularities can be felt.




Finally, the valve seats are clean and tight -- I filled the dome with light oil and nothing seeped through. And there's no sign of combustion leakage at the cylinder head gasket. Only about 2000 miles on this set of Gilardonis --

Any ideas about the reason for low compression?  Does a more experienced eye see problems with piston or cylinder scoring?

[NCAmother]

Are the rings gapped correctly?
Nate

[Testarossa]

Ring gap correct?  I believe so. They're the rings that came with the Gilardoni pistons but I don't think I actually measured them on installation.  Will check.

[oldbike54]

 Seth , did you pressurize the cylinder and see if air was blowing through the muffler or through the carb ?

 Dusty

[Testarossa]

Checked the ring gap: Way too big. Compression rings are .75 and .58 (should be no more than .45).  Oil ring is .7, should be .4.

Thanks, Nate.

Now I'm wondering if I should disassemble the right side even though it shows good compression.

[n3303j]

The vertical scoring looks significant for a Nikasil bore. I've opened up properly running engines with 80,000 miles on them and the cross hatch is still visible and there are no prominent vertical lines.

As previous poster suggested you should pressurize the engine on a compressing stroke and listen at the open carb, exhaust and oil fill plug for air leakage. That will tell you where you are loosing compression.

Your end gaps are beyond published specifications but are probably not the source of enough leakage to cause your running problems.

[pete roper]

The compression test was performed with the throttle wide open or the carburettors removed wasn't it?

[Testarossa]

Engine cold, throttles wide open. Right side was 160psi, left 130psi.  Imbalance was perceptible and running at high rpm was ratty.

Bear in mind that I'm at 5000 feet elevation, so the absolute values for compression are very good, disregarding the imbalance.

I'll pull the right cylinder to see if the cross-hatch is still visible on that side, and measure the ring gaps.

What's the procedure to recondition a scuffed Nikasil bore? 

And is there an easy test for a sticky valve without pulling the valves?   I'm confident that the valves seat properly (Mike Harper rebuilt these heads when I put in the Gilardonis, about 3500 miles back).

The bike was running great before the flood, and only the left cylinder was submerged, so I'm pretty sure the low compression is related to flood damage or to some blunder of mine in the cleanup/rebuild.

[rodekyll]

Engine cold, throttles wide open. Right side was 160psi, left 130psi.  Imbalance was perceptible and running at high rpm was ratty.

Bear in mind that I'm at 5000 feet elevation, so the absolute values for compression are very good, disregarding the imbalance.

I'll pull the right cylinder to see if the cross-hatch is still visible on that side, and measure the ring gaps.

What's the procedure to recondition a scuffed Nikasil bore? 

And is there an easy test for a sticky valve without pulling the valves?   I'm confident that the valves seat properly (Mike Harper rebuilt these heads when I put in the Gilardonis, about 3500 miles back).

The bike was running great before the flood, and only the left cylinder was submerged, so I'm pretty sure the low compression is related to flood damage or to some blunder of mine in the cleanup/rebuild.

You have been told several times what to do by folks who know about these things -- do a leakdown test.  All will be revealed.  I saw a leakdown tester at harbor freight for almost free the other day.

130# is not a bad compression figure.  I think the leakdown test will mostly tell you that you're getting too fixated on numbers.  There are sooooo many other things that will make a bike run ragged, that I'd be looking at almost everything else first.

$0.02

[voncrump]

Did you try to turn the engine over when it had water in the cylinder? The reason I ask this is that I remember the story of a BMW boxer that was dumped in a water crossing. The rider dried it out but it never ran properly. Later in the life of the bike he did an engine job on it and discovered that it had a slightly bent Conrod. From memory it did thousands of kilometres on the bent rod.
This is along shot but not impossible.
Cheers, voncrump

[v65tt]

You sure 130psi is ok? My v7 shows around 230 psi

Have you checked valve seats for damage? If water and silt got in to the cylinder it must have gone in via an open inlet or exhaust valve

Corrosion or a small body hammered into the seat may well cause low readings

Did you turn the engine and hydro lock it before finding the jug full of water, you could have bent a rod or damaged a big end shell causing lower compression reading

[Chuck in Indiana]

It's kind of hard to tell from that picture, but as your ring end gap is too large combined with the vertical scratches on the bore, I'd say you've had some abrasive in there wearing the rings out.
As an aside, a leak down is the second thing I do to determine the condition of an engine. The first is to look at the condition of the plug before doing the leak down.

[Testarossa]

I did NOT turn the crank after the immersion.

I'll button it back up and do a leak-down test, but as noted I've already determined that the valves are seated properly. I do believe that some abrasive wear has occurred. Have ordered a new set of rings.

At 5000 feet elevation, 130psi is roughly equivalent to 155 at sea level; 160 would be about 190 at sea level. Nominally the compression ratio is 9.3:1, which is probably lower than your V7, so I would expect a lower compression test.

[Testarossa]

Went to Harbor Freight, bought the $45 leak-down tester and performed the test. Nice tool!

25% leak-down and the air goes past the piston into the crankcase.  Valves are fine.

So we've confirmed abrasive wear on the rings and Nikasil (thank you, Chuck). Probably didn't get all the grit out of the intake port, because I didn't remove the valves during the rebuild. Lesson learned.

Will install new rings on order. Original question remains: How to recondition the Nikasil.  Most online forums I see recommend wet-buffing with Scotchbrite, then thorough cleaning with WD-40. Consensus on that?  Better idea?

[rodekyll]

Goodonya for getting the leakdown tester!  Now you've got a valuable tool and other guzzisti (the TRUE guzzisti) will make you insanely popular when they come by to jones it.

There is a drill motor-driven hone for cylinders called a 'glaze breaker' that is designed to restore the bore without removing metal.  I have not used it on nickasil, but it works good on iron bores.  Or you could take them to a machine shop and have them hone them. 

[oldbike54]

 There is a ball hone designed to use on Nikasil , although if the coating is scratched it will be necessary to have it re coated .

 Dusty

[Chuck in Indiana]

I dunno anything whatsoever about honing Nikisil. I've not read of anyone doing it.
Edit: after reading Dusty's ball hone thingy, that won't get rid of vertical scratches. I'll bet that cylinder is toast.. well at least needing replated.

[bmc5733946]

What Chuck said, recoat.  I've used a ball hone also known as a "glaze breaker" on Nigusil cylinders to do just that, break the glossy glaze that can accumulate in any cylinder.  Nigusil (Guzzi's name for the coating) is very hard and applied very thinly and takes a certain abrasive quality to remove the glazing and provide some tooth for the new rings.  The coating is probably not thick enough to actually hone out those vertical imperfections, actual honing is done under some heavy pressure and is usually pretty aggressive at material removal.

Brian

[Antietam Classic Cycle]

http://www.mt-llc.com/serviceInfo.php?id=1

[Chuck in Indiana]

^^^^^^
What Charlie says. The did a wonderful job on the blown up Lario cylinder.

[Testarossa]

Thanks. I'll contact Millenium. Their website quotes about $275 to repair. For another $100 I can buy a new cylinder with piston. Does the piston scuffing warrant replacing that too?

[Chuck in Indiana]

Thanks. I'll contact Millenium. Their website quotes about $275 to repair. For another $100 I can buy a new cylinder with piston. Does the piston scuffing warrant replacing that too?

The wear on a piston is normally in the ring grooves. You can check that. Even if it checks ok, considering the general condition of it.. for a hundred bux extra you could have everything new?
Pretty easy decision for me. 
How is the leak down on the other cylinder?

[bmc5733946]

I don't remember what all you did to get it back to running after the flood but I think I would be curious enough to pull the other side after a leakdown test just to eye ball it and the rings.  I think I would also pull the pan and check the rod bearings as it is so easy.  I am very suspicious of wear like that in a cylinder, if caused by debris from the flooding, where else did it travel, once in the oil system there could be quite some damage.

Brian

[Testarossa]

I did check the rod bearings after the flood and they were good. Will look again. 

Because the right side was never under water, was apart for inspection after the flood, and the compression is very good, I have no reason to suspect anything amiss there. But I will do a leak-down test on the right cylinder on Friday or Saturday. If the leak-down test is bad and the rod bearings are good, I may just spring for the 950 kit. If the bearings are bad though I might give up and part it out.

This bike came very close to parting out after the flood, but I now have a lot of time and emotion invested. I was quite proud of the way it ran after I installed the Gilardonis and rebuilt the carbs. Since the flood it's just felt asthmatic.

[Testarossa]

Leak-down on right side is 17%, through the cylinder. Happy silence from the intake and exhaust ports.

Popped the right head off and the cylinder wall has a healthy cross-hatch. I'm going to go for the new cylinder and piston set on the left side.

Next step: drop the pan and check the rod bearings. This may turn into another full rebuild. Should go a lot faster than the last one.

[oldbike54]

 Seth , 17 % is not wonderful .

 Dusty

[Testarossa]

What's a good number?  I know that auto mechanics say a used street engine is good at 15 to 20%, and the FAA allows 25% on a cold engine (60 psi when pressurized at 80 psi).

Meanwhile I'll measure the ring gap.

[Chuck in Indiana]

What's a good number?  I know that auto mechanics say a used street engine is good at 15 to 20%, and the FAA allows 25% on a cold engine (60 psi when pressurized at 80 psi).

Meanwhile I'll measure the ring gap.

Depends on the engine. An 0-470 Continental for instance can be below 80/50. (!) Compression alone is not a cause for an overhaul of them, but they are a strange animal. Just the same, I look with a jaundiced eye at anything below 80/70. If your right cylinder is 80/60, it's probably worn out, too. Sorry, but that's my gut feeling from 1000 miles away and why we do leak downs.

[Testarossa]

Well, 17% is more like 80/66. Recall that compression was 160 psi cold and at 5000 feet ASL.  I'll post a photo of the cylinder and report ring gap, and consider the options.

[lucky phil]

I've pulled many nikasil cylinders off Ducatis and seen vertices markes that look really average but have absolutely no effect on engine performance. We used to call it barcoding and it looked terrible with almost no decernable feel. This barcoding used to happen from new as I had pulled factory built engines apart with virtually zero miles and also my own rebuilds with a few hundred kilometres and found these marks.
Obviously being aware of this I was very careful with tolerances and assembly of my engines but it used to happen anyway.
My suggestion would be to run a flex hone through the bore and not worry too much about the marks , replace the rings, run it in and re check the comp.
Ciao