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#218535 - 10/13/08 3:13 pm JP vs EMGO Piston Weight (regarding crank balance)  
Joined: Apr 2004
Posts: 58
jgrm1 Offline
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jgrm1  Offline
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Posts: 58
Omaha, Nebraska
Does anyone know if there is a significant difference in weight between JP Pistons (from British Only) and EMGO pistons? Is there enough of a weight difference to throw off a crank balance job?

I began building a Triumph 650 engine a couple of years ago and am ready to resume the project. I had the crank balanced using a set of JP 0.040" over pistons that I now cannot locate. I priced a new set of pistons at my local parts house on Saturday, but they only have EMGO pistons.

The good news is the price of EMGO pistons using Harrison rings, at $120, is about half the price of a set of JP pistons and rings. I am happy to save $130, but not if using the EMGOs throws off my crank balancing. Should I cough up the money for another set of JPs or save the money and install the cheaper EMGOs? I do not intend on tearing the bottom end back down to have the crank rebalanced.

As information, I am building this engine in stock form for road use. It is for my 1971 Bonneville.

Thanks,
Jeff

Last edited by jgrm1; 10/13/08 3:14 pm.

2008 Ducati S2R1000
2000 BMW R1100S
1979 Triumph T140E Bonneville 750
1975 BMW R90S
1974 Norton Commando 850
1971 Triumph T120R Bonneville 650
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#218542 - 10/13/08 4:04 pm Re: JP vs EMGO Piston Weight (regarding crank bala [Re: jgrm1]  
Joined: Aug 2007
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Blapper Offline
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Blapper  Offline
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Kent UK
Hi jgrm1,

Quote:
Does anyone know if there is a significant difference in weight between JP Pistons (from British Only) and EMGO pistons? Is there enough of a weight difference to throw off a crank balance job?


For sure and I can say that without knowing the weights or the difference because any difference greater that a few grams will throw it out.

Hopefully somebody will know the details, but what I say stands - more than a few grams and the answer is yes IMHO.

Blapper redwine

#218544 - 10/13/08 4:07 pm Re: JP vs EMGO Piston Weight (regarding crank bala [Re: Blapper]  
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jgrm1 Offline
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jgrm1  Offline
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Joined: Apr 2004
Posts: 58
Omaha, Nebraska
Thanks, Blapper. I am working under the assumption that a new set of JPs will weigh about the same as my original set. Who knows, maybe JP's production methods are not consistent and a new set of JP's might be farther off from my originals than the EMGOs.

-Jeff


2008 Ducati S2R1000
2000 BMW R1100S
1979 Triumph T140E Bonneville 750
1975 BMW R90S
1974 Norton Commando 850
1971 Triumph T120R Bonneville 650
#218545 - 10/13/08 4:10 pm Re: JP vs EMGO Piston Weight (regarding crank bala [Re: jgrm1]  
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Blapper Offline
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Blapper  Offline
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Posts: 4,542
Kent UK
I think that's far more likely than you just being able to interchange them I'm sorry to say.

Good luck!

Blapper redwine

#219657 - 10/20/08 3:40 am Re: JP vs EMGO Piston Weight (regarding crank bala [Re: Blapper]  
Joined: Apr 2004
Posts: 58
jgrm1 Offline
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jgrm1  Offline
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Joined: Apr 2004
Posts: 58
Omaha, Nebraska
I have to wonder just how sensitive the balance job is to a set of pistons. If it is that sensitive, it seems to me we would hear complaints about excess vibration every time oversize pistons are fit. Additionally, it seems the balance factor itself is a bit of a guess. Who knows, perhaps the balance factor I would get fitting the EMGOs with the original balance job may suit my particular bike better. Thoughts?

-Jeff


2008 Ducati S2R1000
2000 BMW R1100S
1979 Triumph T140E Bonneville 750
1975 BMW R90S
1974 Norton Commando 850
1971 Triumph T120R Bonneville 650
#219666 - 10/20/08 6:16 am Re: JP vs EMGO Piston Weight (regarding crank bala [Re: jgrm1]  
Joined: Aug 2007
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Blapper Offline
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Blapper  Offline
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Posts: 4,542
Kent UK
Not impossible, just unlikely. Worst problem is pistons that are a different weight left/right - both the same is not so bad.

Having said that, when you see the extent an expert goes to to get your crank/pistons/rods to the right factor, you'll understand that the difference in weight between one set of piston - esp EMGO's - is a lot.

Blapper redwine

#219680 - 10/20/08 10:10 am Re: JP vs EMGO Piston Weight (regarding crank bala [Re: Blapper]  
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Posts: 160
Paul744 Offline
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Paul744  Offline
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Posts: 160
England
I asked my balancer if I'd need to have a balanced engine tweaked as I was fitting heavier pistons due to a rebore. He said that in an ideal world it should, but in the real world most times people don't notice much difference, as long as the same type of pistons were used (eg cast Heps, JCC, etc, & not some heavy forged jobs). The crucial thing is to make sure that each piston assembly weighs the same, otherwise a rocking effect will be set up (which causes vibes all the way up the rev range).
Heavier pistons will drop the factor slightly & vice versa.
Biggest weight change I ever did was 20g/piston & if there were any vibe differences due to it then they weren't anything to worry about (normal road use).
hth


Last edited by Paul744; 10/20/08 10:27 am.
#219843 - 10/21/08 11:18 am Re: JP vs EMGO Piston Weight (regarding crank bala [Re: Paul744]  
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Blapper Offline
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Blapper  Offline
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Joined: Aug 2007
Posts: 4,542
Kent UK
Hi Paul,

20gms a piston - interesting. Do you have any idea what the weight difference would be between the std Heps and EMGO's? Looks vast to me.

Blapper redwine

#219890 - 10/21/08 3:37 pm Re: JP vs EMGO Piston Weight (regarding crank bala [Re: Blapper]  
Joined: Apr 2004
Posts: 58
jgrm1 Offline
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jgrm1  Offline
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Joined: Apr 2004
Posts: 58
Omaha, Nebraska
That would be good to know. Anyone have two similar sized EMGOs and JP/Hepos to compare? Even if they aren't +0.040 for a Triumph 650, it might give me an idea of the difference I am facing.

Thanks,
Jeff


2008 Ducati S2R1000
2000 BMW R1100S
1979 Triumph T140E Bonneville 750
1975 BMW R90S
1974 Norton Commando 850
1971 Triumph T120R Bonneville 650

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