Top end work

[Tom M]

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.

 

In the pic above with the FBF piston next to the Guzzi piston it appears to me that the FBF is perfectly round with no reliefs on the wrist pin sides of the piston. The picture of your FBF piston has reliefs on the sides.

[raz]

In the pic above with the FBF piston next to the Guzzi piston it appears to me that the FBF is perfectly round with no reliefs on the wrist pin sides of the piston. The picture of your FBF piston has reliefs on the sides.

Blimey, you're right! Maybe they look more like the flat top ones in that respect. I'll have a look and take some more pictures.

 

After all, it's winter and we should dissect things like this down to last molecules

[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.

 

I checked for the radius and it's definitely there. I also checked the faces a little closer and noticed that I did have a small pit or two on both exhaust followers, but both intakes were clean. Here are a few pics of one of the followers with a little pit. I expect this means I should change them before it gets worse or damages the cam?

 

 

[Tom M]

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?

 

I got the FBF pistons and they don't look anything like the picture on their web page. They look like the ones from the old thread with a high dome and no reliefs around the wrist pin. This is not what I wanted or expected so I am sending them back. The picture on their web page is the Cali piston. Guzzirider told me that his pistons had Wiseco markings on them, the set that I received does not. I suspect his and the ones Raz got are a newer design than what I got.

 

I did not get a chance to weigh them Ernst but I did take a quick measurement on the skirt length and it is 3mm shorter than the stock piston. I took some pictures of the two next to each other for anyone who cares to see the differences between the two.

On the bench

 

From the bottom

 

With wrist pin connecting the two to show dome height difference

 

Bottom with wrist pins removed. I didn't take a side shot but the FBF wrist pin has a smaller ID than stock.

 

My plan now is to reuse the stock pistons after having their skirts recoated and the domes ceramic coated unless Mike Rich comes through with a new batch of pistons very soon.

[luhbo]

I checked for the radius and it's definitely there....

 

 

Taking this picture exactly against this backround is a clever idea. The reflection lines give a good impression of the radius.

 

Hubert

[Tom M]

Taking this picture exactly against this backround is a clever idea. The reflection lines give a good impression of the radius.

 

Hubert

 

I wish I was that clever but it was just a coincidence that I had a pad of graph paper laying around. I was just trying to get a decent picture of the pit on the face of the lifter.

 

What do you think of the pit?

[luhbo]

I'd not replace them. Just from sight they are still perfect, and as Greg already mentioned, even "worn" like the ones of Raz they can still work well for a long time.

On the other hand, they are not very expensive, so if you are a person a bit nervous ...

 

You should definitely put those FBF aluminium lumps on a scale before you send them back. The scale probably needs not to be very accurate.

 

Hubert

[Tom M]

I'd not replace them. Just from sight they are still perfect, and as Greg already mentioned, even "worn" like the ones of Raz they can still work well for a long time.

On the other hand, they are not very expensive, so if you are a person a bit nervous ...

 

You should definitely put those FBF aluminium lumps on a scale before you send them back. The scale probably needs not to be very accurate.

 

Hubert

 

With rings, wristpins, and circlips:

FBF = 586.5 grams, used stock Guzzi (D class) = 604.6 grams according to a shipping scale at my workplace. The FBF was 18g lighter.

 

Anybody else care to weigh in on my cam follower picture above?

[luhbo]

Funny. The FBF looks as if it was at least 50gr heavier. I assume that the pins are more or less the same.

 

Hubert

[Tom M]

I assume that the pins are more or less the same.

 

The FBF wrist pin had a much larger ID than stock so I'm sure it was lighter.

[raz]

Considerably lighter. I think that is the better part of the total wight difference.

 

Stock pin (at least mine¹⁾) is 58.05 mm long, ID 13.4 mm

FBF pin (at least mine²⁾) is 63.5 mm long but ID is 15 mm in the middle, tapered out to 18.6 mm in the ends (nominal OD is 22 mm)

 

 

¹⁾ 1100 Sport

²⁾ My FBF boxes says "V-11 F27700" if that is any indication of version

[Tom M]

Progress Report:

Mike Rich finally got enough orders for another run of pistons back in January (thanks Slavek) so I bought a set. I had his vendor that applies the anti-friction coating on the skirts apply a thermal barrier coating to the crown too. Mike said he doesn't typically offer the crown coating because it didn't show any power gain on the dyno, but I'm not looking for more power with it, I'm looking to eliminate my pinging problems. Vendors who offer this coating claim it reduces the likelyhood of pinging so I'm going to give it a try.

 

I sent my heads to a local machine shop to have them replace the valves and do whatever else was needed. Turns out I needed valve guides and valve springs. The guides I expected but the springs were a complete surprise. The shop said mine were out of spec so I'm getting new ones. Greg Field cut me a great deal on a set that were installed in a head but never run. Thanks Greg!

 

I'll be picking up the heads this week and hope to have everything back together in a few weeks.

 

Here are some pics of the MR piston next to my stocker. FWIW it weighs 586 grams with pin, clips and rings. I used the Raz trick of connecting the two pistons with a wrist pin in a few of the shots. It's easy to see the bevel that he uses to match the chamfer in the combustion chamber, and to see that the dome on his pistons is lower than stock. I really really hope this means no more pinging for me!

 

 

 

 

 

[raz]

Nice!

 

That MR piston dome would hit the hemi wall in a decked head, wouldn't it? It is low but very wide. My OEM piston squish band is 7 mm in from the circumference, MR look like half of that tops. But that is only logical since it was made for the stock heads.

[Tom M]

Nice!

 

That MR piston dome would hit the hemi wall in a decked head, wouldn't it? It is low but very wide. My OEM piston squish band is 7 mm in from the circumference, MR look like half of that tops. But that is only logical since it was made for the stock heads.

 

I don't know if there would be a clearance issue there Raz. I'm sure Mike could tell someone how much material could safely be removed from the head before things get too tight in there, or someone could use clay to check the clearance if there were any doubts when assembling the engine.

 

How are you coming on your rebuild?

[docc]

Tom,

 

Thanks for the update. What kind of valves?