Top end work

[luhbo]

...

Here is my right piston compared to an FBF one. ....

 

What is the diameter compared to the original one?

 

Hubert

[Dan M]

 

Does anyone know why on both pistons, the amber colour is below second compression ring, but not between first and second?

 

Looks typical. There is very little oil above the oil ring but not between the compression rings leaving the amber discoloring. Below the oil ring on the skirt there is much more oil and it stays cooler. (no discoloring)

[raz]

What is the diameter compared to the original one?

 

Hubert

I don't have the means to measure that. Checking with a vernier caliper they are exactly the same, but that's just down to 0.05 mm.

 

I have size "A" cylinders and pistons, the smallest. FBF just sell one size for what I know.

[motoguzznix]

Tom

 

be careful concerning the FBF pistons.

These pistons are of a very unfavorable design for the V11 engine.

 

First point is you have to mill off the cylinder barrels to get the pistons flush on top. The photo shoot above suggests the same compression height for the stock and the FBF piston, so the same amount has to be removed from the barrels for both oof them.

Second point you have to mill off 1 mm from the heads to get a working squish area. Remember the chamfer.

Both measures increse the CR of the engine. Both measures are necessary to get a correct working combustion chamber design.

Third point the FBF piston in addition raises the CR further. But the higher dome makes the combustion chamber worse and more prone to ping.

So you have 3 measures that increase CR and thus pinging,

Fourth point the higher dome worsens things further.

 

If all is done correctly, there are two measures that detract from the pinging issue:

Valve stem play like new prevents the oil contamination of the combustion chamber.

The now existing squish makes the mixture in the comb chamber less prone to ping.

 

The extra CR of the FBF pistons is not an asset for me.

Maybe the CR gets so high that even twin spark is unable to cope with this engine. And without the ability to change the ignition map there is no way to make this setup work.

 

Why not proceed with the stock pistons? They don't look bad, the missing coating is no real problem. If the play is within the wear target, there is no reason to throw them away. Or mill off some mm from the FBF piston dome if possible.

[Tom M]

Ernst,

I believe FBF changed their piston design a while back. If you compare the pistons pictured on their website to the pictures that have been shown in the thread below you will see that their latest design has a dome shape like the Mike Rich pistons, not like their older high dome pistons. There have been a number of guys that I know of (Guzzirider for one) that have seen good results by just installing the newer FBF pistons without doing any extra machine work to the heads or cylinders. That said, I will measure everything to the best of my ability to make sure the pistons fit the bores correctly and have the proper squish clearance in the head.

 

I understand why you advocate machining the chamfer in the head away but that removes a lot of material that will need to be compensated for with a much thicker gaskets. I'd like to avoid that extra machine work if possible.

 

I won't be throwing away my old pistons. If I'm not happy with the FBF setup I can always go back to the stockers.

 

Newer FBF pistons. Note the low dome height:

 

Old piston comparison pic from old thread here:

 

More recent piston thread with Guzzirider info:

http://www.v11lemans.com/forums/index.php?...mp;hl=Mike+Rich

 

I also spoke with a local Guzzi guy who's friend installed the FBF pistons a little while back and he's very happy with them too.

 

I know I didn't need new pistons but I figured as long as I've got the engine open and happen to have the money available a little more power will mean a little more fun for me . As I said at the beginning of this thread the only reason I'm even in there right now is because I'm sick of the pinging. I wanted to install the Mike Rich pistons last winter for the same reason but they weren't available then and still aren't now.

 

Thanks for your input!

[Guzzirider]

Yes the FBF pistons fitted to my bike (and Mal's) were a simple swap- no other work needed. I did get the ECU reflashed with Ultimap software and get the bike set up on HTM's dyno afterwards but Mal never bothered and his runs fine.

 

I think I have posted the dyno chart a few years back on this forum- no extra peak bhp but useful extra shove throughout the midrange. I am sure there are better and more sophisticated ways of eeeking out extra grunt but the piston swap was a very cost effective way of getting a bit more zap just where you want it.

 

The only downside is that she does pink on cheapo fuel but its hard to find a fuel station these days that does not sell high octane.

 

Thinking back to the debates on that old thread, it should have blown up by now

[Greg Field]

left piston after 50.000km

I use 20w-50 oil

change every 5000km

valve clearance is factory standart

 

left piston where oil has been running to the cilinder

 

right piston, also small leak through gasket

 

another view

 

 

and I wonder where did I get the line on the right bottom corner of the piston... no damage to the barrel visible

 

Slavomir:

 

Look at all that chocolate on both pistons all the way down to the oil rings. Your rings never did seat, or you've been running it a long time after it lost ring seal.

[Greg Field]

will do next year! it is much better when you see the results (dont wanna open the oil pandora box again) so let's see how the pistons gonna look like after another 20.000km next year

 

Slavomir: Use new rings. Install them dry. Your engines main problem appears to have been complete lack of ring seating.

[Slavomir Musilek (R.I.P.)]

Slavomir: Use new rings. Install them dry. Your engines main problem appears to have been complete lack of ring seating.

 

thx! I would not use the old ones either.

[Greg Field]

Does anyone know why on both pistons, the amber colour is below second compression ring, but not between first and second?

 

Usually, that means you oil rings aren't as sealed as they should be.

[Greg Field]

Same here. Mine looked great. I can take a pic if you like.

 

I saw your pics in the other thread, those exhaust followers look nasty. I'm surprised your cam is OK. Hopefully Pete or Greg will chime in on your other threads.

 

Clear is good. They must also retain the radius on the bottom. To check them, put two of them face-to-face. Hold their inter face up to a strong light. Light should shine through a narrow gap between them, except at the very small part of the faces where they actually touch. "rock" them against one another, and you will se the gap narrow on one side and widen on the other. If the gap doesn't do this, they're worn too flat for safe re-use.

[Tom M]

Clear is good. They must also retain the radius on the bottom. To check them, put two of them face-to-face. Hold their inter face up to a strong light. Light should shine through a narrow gap between them, except at the very small part of the faces where they actually touch. "rock" them against one another, and you will se the gap narrow on one side and widen on the other. If the gap doesn't do this, they're worn too flat for safe re-use.

 

Good stuff Greg. Thanks. I'll check them out this weekend.

[motoguzznix]

Ernst,

I believe FBF changed their piston design a while back. If you compare the pistons pictured on their website to the pictures that have been shown in the thread below you will see that their latest design has a dome shape like the Mike Rich pistons, not like their older high dome pistons. There have been a number of guys that I know of (Guzzirider for one) that have seen good results by just installing the newer FBF pistons without doing any extra machine work to the heads or cylinders. That said, I will measure everything to the best of my ability to make sure the pistons fit the bores correctly and have the proper squish clearance in the head.

 

I understand why you advocate machining the chamfer in the head away but that removes a lot of material that will need to be compensated for with a much thicker gaskets. I'd like to avoid that extra machine work if possible.

 

I won't be throwing away my old pistons. If I'm not happy with the FBF setup I can always go back to the stockers.

 

Newer FBF pistons. Note the low dome height:

 

Old piston comparison pic from old thread here:

 

More recent piston thread with Guzzirider info:

http://www.v11lemans.com/forums/index.php?...mp;hl=Mike+Rich

 

I also spoke with a local Guzzi guy who's friend installed the FBF pistons a little while back and he's very happy with them too.

 

I know I didn't need new pistons but I figured as long as I've got the engine open and happen to have the money available a little more power will mean a little more fun for me . As I said at the beginning of this thread the only reason I'm even in there right now is because I'm sick of the pinging. I wanted to install the Mike Rich pistons last winter for the same reason but they weren't available then and still aren't now.

 

Thanks for your input!

Tom

 

Those new pistons are indeed a completely different design compared to the older ones.

Apart from the fact the newer ones are sliper pistons, the dome height seems to be lower than stock. Maybe these pistons reduce CR. They look like the high compression pistons for the Cali 1100. That explains why they can be used without any other mods on the engine.

For your understanding: There is no squish without machining the heads. Believe it or not, the engine would benefit from squish an the ping issue would decrease. And you have not to compensate for the reduced thickness with the gaskets - you would loose the raised compression and the bigger squish height would make the squish inefficient.

 

One question: Could you measure the weight of these pistons and the stock items? And post the figures here? The stock ones are very heavy and the piston pin too. Maybe in that area gains are to be made?

[Tom M]

One question: Could you measure the weight of these pistons and the stock items? And post the figures here? The stock ones are very heavy and the piston pin too. Maybe in that area gains are to be made?

 

Sure. I'll take some pics to show how they compare to the stockers and see if I can find an accurate scale. I wouldn't expect them to weigh less than the stock pistons because that would cause an imbalance with the crank, wouldn't it?

 

Raz posted a pic toward the bottom of page 1 of this thread that shows an FBF piston that he bought from Antonio. That one looks different from either of the FBF pistons shown above!

[raz]

Raz posted a pic toward the bottom of page 1 of this thread that shows an FBF piston that he bought from Antonio. That one looks different from either of the FBF pistons shown above!

I think it's the same model as in the older comparison picture with amber text. It's just that I had them at right angle from the gudgeon pin.

 

The other picture showing a flatter FBF piston, are you sure it's not a Cali one? They are separate items but described in the same block of text. (Edit: never mind, it should be 11:1 anyway)