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Mike Rich pistons


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Hi Kevin_T, When I weighed the piston the gudgeon pin was in place, the piston & rings minus the pin is 488gms & the gudgeon pin weighs 91gms (metric), I don’t know what the Oem piston weighs but I was under the impression that they were exactly the same as the MR piston.  The difference between yours & the MR piston is quite surprising. Could it be down to US grams & metric grams..?


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Thanks for the picture. I'm surprise at how sharp the valve cutouts are. I'd imagine setting up squish would be very important. The dome is very flat, flatter then the Oem piston got to help with flame spread. Hemi heads are legendary for being able to fill a cylinder. They're also legendary for not being able to burn everything they take in.

My Oem piston is lighter @ 457.2 grams the wrist pin was heavier @ 106.9. If you install those pistons do yourself a favor and put some money in the budget for a balance job.

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On 12/1/2023 at 3:52 PM, Eamonn said:

With regards to how the bike runs, more gee gees etc.? Would it be a recommended mod.?

Hi Eamonn

Your query re MRM hi-comp pistons.

Yes. Absolutely. I will answer from memory here… you can always check by going over old posts yourself 

I seem to recall years ago when I ordered my pistons there were a couple of weight versions - one being comparable to oem stock weight in replacement & the other being further lightened. The piston profile of the two were the same tho.

The V11 combustion chamber differed from previous Guzzi big blocks by having a angled squish band designed into it.
I won’t try & relay here the details of the benefits this gives but at the time I researched it extensively because I enjoy understanding the nitty gritty (my ocd kicks in) - but essentially it improves air/fuel mixture turbulence & homogenisation than flat squish band at the higher RPM’s which Guzzi was trying to improve upon for the V11 design.

Remember also it was changing to fuel injection from carburettor too on the V11 models. This was all happening at the time of Aprilia taking ownership as well. I digress.

However - there seems to have been either a cost cutting exercise going on or an ordering oversight boo-boo stuff up of sorts & the pistons design wasn’t changed to properly match with the angled squish band heads.

So while the heads squish band surface was angled the piston squish band was flat resulting in an ineffective non-working squish action. This mismatch is the root of the V11 tendency to detonate under certain conditions . I digress again.

Anyhow Mike Rich spotted the design nuances of the V11 head chamber squish angle & designed his pistons with the same matching angled squish to work properly with the V11 heads which the Guzzi factory had ultimately failed to ever rectify.
Improved piston chamber turbulence dampens detonation occurring & allowed a slightly higher compression ratio to be achieved as well with Mike’s hi-comp design.

Whew! Sorry that the basic backstory from memory took so long Eamonn.

Anyhooo… at the time I think a member called helicopterJim had previously installed MRM pistons & his positive commentary on his experience probably influenced my own decision to go ahead with Mike’s pistons.

I chose the standard weight MRM pistons as I didn’t want to be bothered with any extra hassle of balancing work costs.

I noted Pete Roper rating Guzzi conrods as very strong, very good & so had no desire to additionally fork out for Carillo’s in that case.

The piston’s had a noticeably positive impact on installation. A slightly sharper bark with a more ‘awake’ feel & pulls harder thru midrange & sustains it longer imo. The occasional detonation rattle reduced to almost never - maybe once in a year of riding I’d notice a little rattle rattle for a second or so… that’s it even in hot 100F days. And that was before a better Bosch O2 sensor which improved the ECU control.

My bike has the 15RC ECU so it continually trims the fuel when changes are made so it has capacity to recalibrate itself to it’s desired Lambda ratio in time.

I seem to recall American V11 owners who installed Mike’s pistons without retuning their ECU’s & their bike’s coped fine with improvement but maybe others can confirm this recollection.

In short - go ahead & install the pistons. They are an improvement. Oh, I just remembered - they are forged & a little clickety clackety mechanically louder for a couple of minutes until the combustion heat expands them just ever so slightly & that mechanical clatter completely disappears.

Hope that helps 

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Hey ScuRoo, thanks so much for the comprehensive response, it sounds like they get the tick of approval, your insights are very much appreciated, I’ll report back when I get around to installing them. 

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  • 2 weeks later...

@Eamonn, you should email Mike Rich and get a list together of questions before hand. Like if you need to check valve to piston clearance or what's the best way to seat rings. You talked about doing some head work he might do that I just know he doesn't want to be a parts supplier. Super nice and his website is up so he can't blame you for inquiring.

Let us know what you found for weights on the 2004 Guzzi parts I only had my 2002 for comparison.



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On 12/22/2023 at 9:03 PM, Eamonn said:





Kevin’s article adds explanation to the MR hi-comp chamber/piston improvements that assists combustion & increases compression

Well worth a thoughtful contemplation 

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Rebalancing for piston weight is really a non-issue. Anybody who has talked to professional tuners knows there is a wide range of balance factors for single and twin cylinder engines; the longer the crankshaft, the more critical balance becomes due to torsional harmonics, number of main bearings etc. But for our big dumb lumps, there's a generic recipe for 90* twins, and some accommodation for the resonance in the frame for felt vibration. In my '85 LM1000, I installed Carrillo rods under the stock pistons without a rebalance, and it became dead smooth at all RPMs, losing the annoying handlebar vibration around 4000 rpm. I was as surprised as anyone. Balance factor has only 2 functions, comfort and mechanical durability; for instance, old British twins would literally break the crankcases if the balance factor got too far away from 50% (iirc) On something like a big block 'Guzzi or H-D Sportster, the crank and cases are so overbuilt it's simply not a structural issue. For me, I would never tear down an engine to rebalance it unless it proved uncomfortable, or if it was going to be thrashed within an inch of it's life at maximum effort. 

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