Soft valve stems & plasticine guides?

[dlaing]

All good stuff, MGNX. Thanks again. 1 mm squish squares exactly with the recommendation of a "local", yet world-renowned Guzzi machinist at .040".

So, now Ratchet wants to RAISE the compression????

Is there some benefit of thinner gaskets rather than forged high compression pistons if the compression ratio ends up being the same???

What is going on here?

I though thicker gaskets reduced pinging??????????

[Rusty Bucket]

So, now Ratchet wants to RAISE the compression????

Is there some benefit of thinner gaskets rather than forged high compression pistons if the compression ratio ends up being the same???

What is going on here?

I though thicker gaskets reduced pinging??????????

 

A 'near collision' (.024-.040") between the piston and the head at TDC cools the piston (by proximity), drives the igniting mixture into a smaller area (hopefully into an area with a centralized ignition source for a faster burn), induces a shockwave that helps keep mixture in suspension and helps eliminate unburned mixture in crevass areas, and will, when everything is correct allow the highest possible static and dynamic compression ratio, which makes for a clean combustion chamber with a high output and excellent fuel efficiency. The downside? Careful assembly and tedious fitting required as 'hopefully close enough' can be worse that not attempting to get things right at all. At some point, your near collision between piston and head becomes a clear miss, and you have added crevass area to the chamber, and provided area where carbon will have an easy time adhereing as we are far from the flame front; the surface runs cold, unburned mixture lurks waiting for a chance to start an abnormal combustion event. See a low compression BMW R-series chamber from the early '80's to see how badly the same basic parts can be arranged. Cold, dirty-running, poor atomization in slow moving ports, low output and weak mileage, and VERY octane sensitive.

The substitution of a thicker gasket in a chamber that been optomized for a thinner one could make the engine ping worse, in theory.

[dlaing]

snip

Thanks!

Excellent response

I wonder how to analyze the burn pattern on the piston????????

[big J]

Simple,make a glass cylinder head.

 

Jeez,Dave

[Guest Nogbad]

Thanks!

Excellent response

I wonder how to analyze the burn pattern on the piston????????

 

It's called laser anemometry. Special cylinder head needed and equipment costing many hundreds of thousand pounds. It would only prove that the Guzzi engine is old, tired and inefficient. Things we knew already.

[pete roper]

It's called laser anemometry. Special cylinder head needed and equipment costing many hundreds of thousand pounds. It would only prove that the Guzzi engine is old, tired and inefficient. Things we knew already.

 

Or, alternatively, you can take the head off and use your eyes

 

No I'm not being facetious, you can get a pretty good idea of what is going on by removing the head and examining the combustion chamber and top of the piston.

 

If you have the squish set correctly the squish area, which is the flat bit surrounding the dome that comes up into close proximity with the head, should be pretty much clean with no carbon deposits on it to speak of. You will usually find, even with the best set up motor that there will be slightly more contamination on the squish area on the non-thrust side of the piston, (Scratches his head trying to work it out, not having ancient text book to hand ) as this is the side more likely to cant away from the head under load.

 

The previous description of why squish is so important is excellent, as is the eample of Lo-Po bimmer heads, which are awful! Compare them to the infinitely superior Guzzi smallvalve head design and it's easy to see where they went horribly wrong To add to it though having the squish set to wide also allows the retention of pockets of fresh charge polluting, un-expelled, left over exhaust gas in the area betwixt piston deck and head. This is the 'End Gas', (Fart jokes start here, please take them to the banter forum.) and it will be a MAJOR contributor to detonation and other wonky-burn related problems.

 

You can also, if you take the heads off after a short period of running examine the combustion chambers and valves for evidence of 'Wetting Out' the deposition of unburnt fuel onto the walls of the combustion chamber where it's vaporisation is wasted cooling the surface of the head, (And leaving deposits.) rather than cooling the charge itself, sorry, I digress.

 

One thing that has to be taken into account with any Guzzi engine up to the latest itterations as fitted in the Breva and Griso is that they use Kingerlite gaskets and these have the annoying trait of compressing in service. This makes setting up the squish a right royal pain in the arse unless you KNOW exactly how much they are going to compress. I had the squish set up very precisely and had re-torqued the heads several times and re-checked it but after two meetings Rob did a re-torque and it then ate it's big ends. The squish clearance had reduced just enough that at max RPM crank whip and rod stretch were sufficient to allow the pistons to just kiss the head. Not enough to even damage the pistons, the rings were all still free in the grooves and their clearance wasn't affected, but enough to destroy the oil film on the big ends. Luckily Rob caught it before the bearing clearance could get excessive to the point where the pistons were damaged, but it was luck rather than judgement!

 

The happy news is that unless there is something I'm missing I can see absolutely no reason why V11 owners who want to go to the effort to do the job properly shouldn't use the Breva/Griso gaskets. These are a steel 'Mono-Torque' gasket that won't crush. You might even find, given that as far as heads and barrels are concerned there are few differences between the V11's and the later models, that simply slipping the gaskets in will get the squish pretty close to right. Gillardoni, who make all of Guzzi's, (And BMW's!) barrels have always been pretty good at consistently getting the barrel depth correct, consistent and accurate so they might be a simple bolt in. HAving said that the thickness of these gaskets will be less than Kingerlite ones so assembling the barrels and heads onto the block once and measuring the squish would allow you to ascertain exactly how much was needed to be removed from the bottom of the barrel to get the squish correct, then the motor could be built and you'd know once and for all that it was right and you wouldn't have the fear of the pistons kissing the heads as a.) no re-torquing is neccessary and b.) the gaskets are incompressible.

 

Gotta go.....

 

Pete

[Guest ratchethack]

Now I've never done this, but I've heard mention of it many times as a viable technique. I don't see why it wouldn't work. Any pro or con commentary - if not direct experience - would be most appreciated.

 

The drill is to use a length of the proper diameter solder in a similar manner as "plastigauge" through the spark plug hole to get a quick and accurate read on squish clearance. The difference, of course, is that the dimension is measured directly on the solder, whereas with plastigauge, it's more accurately translated by the width of the plastic to a conversion chart (not the depth of the material itself).

 

Why not??

 

[motoguzznix]

Pete

 

setting the squish correctly is always a good idea.

When I put' new cylinders on my good old Le Mans 2, the pistons in the new gilardonis were 0,7 mm below the top. Add now an aftermarket gasket with approx 1,5mm when compressed, the squish thickness is 2.2 mm! Thats very far from the truth.

 

The example stated before won't cause any damage on the engine, but this is one of the reasons why "straight bolt ons" do not exist any more in my book. When something does not work in my engine that was "Bolt on" then I am responsible for that, not the manufacturer!

[mike wilson]

Now I've never done this, but I've heard mention of it many times as a viable technique. I don't see why it wouldn't work. Any pro or con commentary - if not direct experience - would be most appreciated.

 

The drill is to use a length of the proper diameter solder in a similar manner as "plastigauge" through the spark plug hole to get a quick and accurate read on squish clearance. The difference, of course, is that the dimension is measured directly on the solder, whereas with plastigauge, it's more accurately translated by the width of the plastic to a conversion chart (not the depth of the material itself).

 

Why not??

 

 

Done it regularly on (whisper it) two strokes. It's the recommended technique for measuring MZ squish. If it's good enough for Walter Kaaden, I don't think there is anyone here qualified to naysay it.

 

mike

[Guest ratchethack]

Done it regularly on (whisper it) two strokes. It's the recommended technique for measuring MZ squish. If it's good enough for Walter Kaaden, I don't think there is anyone here qualified to naysay it.

 

mike

Thanks, Mike. Have you measured y'er Guzzi's squish this way? If so, I'm more'n curious about what actual measurement and right-left variance might be expected from Mandello??

 

Frankly, I'm a little squeamish about the prospect of possibly shearing off a chunk of solder and then having to go on an extended fishin' expedition to get it out. Yeah, I know - theoretically, if it shears off, I've got a real problem with squish clearance anyway. . . . .

 

But if this is a viable, low-risk technique on V11's, I'd like to get a read and compare it to what others get if at all possible.

 

TIA

[V11UK]

KR Green 1999/2000: actually 62000 km, valves adjusted once a year, engine/drive-train no recall, still working fine !

 

KR Green 1999: 76,000 km, valves adjusted once a year, all engine/drive train recalls done, still working fine!

 

I'm a bit late to this topic but the 'soft valves' story has been in the back of mind for sometime and I was going to have the heads refurbished this coming winter just as a precaution. It would appear that the old adage of 'if ain't boken don't fix it 'applies here.............

[luhbo]

For me it's the first bike I didn't open the first winter I had it. Now the fourth is coming (10°C this night) and I must admit I tend to give up. But I have an alibi: I'm thinking about a twin spark conversion.