Author Topic: Big bore question  (Read 905 times)

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JessHerbst

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on: November 22, 2022, 01:39:08 am
 After reading the article about the new Suzuki parallel twin I’m curious about balance.
 If you change the pistons and/or connecting rods, is the balance shaft still in balance?
 
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Wrenchjockie

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Reply #1 on: November 22, 2022, 02:18:57 am
Depends on if the new bits weigh the same as the old ones.


lucky phil

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Reply #2 on: November 22, 2022, 10:27:00 pm
After reading the article about the new Suzuki parallel twin I’m curious about balance.
 If you change the pistons and/or connecting rods, is the balance shaft still in balance?
 

Wrenchjocky is correct. The new piston assembly and rings need to be the same weight as the originals or very close to it to maintain the original balance and vibration characteristics. If you change the rods as well then you'll need to rebalance the crank and balancer or put up with the imbalance induced vibration. On my Sunday drive car (2.3 litre turbo 4 cylinder flat plane crank with balancer) some of the more performance orientated owner do a balance shaft delete mod. Just unbolt the balancer assembly and remover it. They report greater NVH but for them it's tolerable for the added few HP. 

Phil
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JessHerbst

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Reply #3 on: November 22, 2022, 10:29:51 pm
Wrenchjocky is correct. The new piston assembly and rings need to be the same weight as the originals or very close to it to maintain the original balance and vibration characteristics. If you change the rods as well then you'll need to rebalance the crank and balancer or put up with the imbalance induced vibration. On my Sunday drive car (2.3 litre turbo 4 cylinder flat plane crank with balancer) some of the more performance orientated owner do a balance shaft delete mod. Just unbolt the balancer assembly and remover it. They report greater NVH but for them it's tolerable for the added few HP. 

Phil
So this is what I thought. I see lots of posts about ‘big bore’ & ‘high compression’ kits for the 650, and I wonder if any of those parts have had any attempts at matching the weight of the parts they replace.
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lucky phil

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Reply #4 on: November 22, 2022, 11:07:06 pm
So this is what I thought. I see lots of posts about ‘big bore’ & ‘high compression’ kits for the 650, and I wonder if any of those parts have had any attempts at matching the weight of the parts they replace.

They should but who knows? High comp and big bore pistons are traditionally of higher quality materials and often forged instead of cast so there is wriggle room for the bigger pistons while keeping the overall reciprocating mass the same. However these days with higher quality stock parts being used some of that wriggle room may be disappearing. So then you get pistons with less skirt and support to match the originals weight when you go bigger and this leads to more piston/engine noise which may not please the average road user. Cast pistons these days are getting very good and forged are often heavier.
The truth is people generally aren't interested in asking the sort of questions you have asked so you can sell them anything with the possible resulting consequences. Then when they get the modification they are reluctant to mention any down side for fear of looking foolish. Modification feedback from customers on the internet is almost pointless these days I find, so who knows what the NVH is like with some big bore mods etc.

Phil     
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Shifty1969

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Reply #5 on: November 22, 2022, 11:22:51 pm
If the weight difference were slight enough, would it be possible to rebalance the weight by dimpling the opposite side with a drill, this used to work on Harley flywheels?
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lucky phil

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Reply #6 on: November 23, 2022, 01:19:27 am
If the weight difference were slight enough, would it be possible to rebalance the weight by dimpling the opposite side with a drill, this used to work on Harley flywheels?

Thats the std methodology to remove weight. Sometimes you need to add weight so you cross drill the crank bob weight and add a slug of Mallory metal.

Phil
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NJ Mike

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Reply #7 on: November 23, 2022, 03:27:04 am
So this is what I thought. I see lots of posts about ‘big bore’ & ‘high compression’ kits for the 650, and I wonder if any of those parts have had any attempts at matching the weight of the parts they replace.

I put the high compression pistons in my bike and there was no difference in the vibration from the stock pistons, which was very slight in the left grip causing a tendency for my hand to tingle a bit. Wrenchjockie weighed the HC pistons and they were virtually identical.

My tuner however was able to tune each cylinder separately, they were different, and that completely eliminated even the very slight buzz I felt in my left hand. Now it's glass smooth, no vibes anywhere in the power band.
Been riding since 1980. Live in Bloomfield, NJ.

Current Ride: 2019 RE Conti GT 650

Past Rides: 2002 SV 650, 2001 Moto-Guzzi V11 Sport, 1985 BMW K75, 1992 Honda 750 Nighthawk, 1982 Yamaha Vision, 1981 Kawasaki GPZ 550, 1978 Honda 750F, 1980 Honda 650


Racer57

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Reply #8 on: November 24, 2022, 04:15:24 am
I put the high compression pistons in my bike and there was no difference in the vibration from the stock pistons, which was very slight in the left grip causing a tendency for my hand to tingle a bit. Wrenchjockie weighed the HC pistons and they were virtually identical.

My tuner however was able to tune each cylinder separately, they were different, and that completely eliminated even the very slight buzz I felt in my left hand. Now it's glass smooth, no vibes anywhere in the power band.
Does your tuner change timing/ignition ? No one that I have been in touch with has a map for sale for hi-comp pistons which would require it.


RecoilRob

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Reply #9 on: November 24, 2022, 02:26:42 pm
Does your tuner change timing/ignition ? No one that I have been in touch with has a map for sale for hi-comp pistons which would require it.

He is flashing the ECU so the timing can be changed....unlike the Power Commander which cannot alter the timing.   If you can find a PowerTronic unit it can adjust both fueling and timing.


Racer57

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Reply #10 on: November 24, 2022, 03:09:41 pm
He is flashing the ECU so the timing can be changed....unlike the Power Commander which cannot alter the timing.   If you can find a PowerTronic unit it can adjust both fueling and timing.

True, but without access to a dyno you could detonate the engine.   :D


NJ Mike

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Reply #11 on: November 25, 2022, 02:23:40 pm
Does your tuner change timing/ignition ? No one that I have been in touch with has a map for sale for hi-comp pistons which would require it.

Yes, he changed the ignition timing and was able to fine tune it much more than what the PC would allow. As far as the PowerTronic, good luck finding anyone in the US that will touch it. Plus, by tuning the ECU you don't have to worry about the piggyback unit croaking out on you. It happens far more than you might realize. And when it goes, you're back to the stock map without even knowing it. It doesn't give you a warning sign, it just goes offline. The bike starts to run bad, and with significant changes to your motor, you'd run a good chance of causing significant damage due to very lean running.
Been riding since 1980. Live in Bloomfield, NJ.

Current Ride: 2019 RE Conti GT 650

Past Rides: 2002 SV 650, 2001 Moto-Guzzi V11 Sport, 1985 BMW K75, 1992 Honda 750 Nighthawk, 1982 Yamaha Vision, 1981 Kawasaki GPZ 550, 1978 Honda 750F, 1980 Honda 650


gizzo

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Reply #12 on: November 25, 2022, 09:29:25 pm
Yes, he changed the ignition timing and was able to fine tune it much more than what the PC would allow. As far as the PowerTronic, good luck finding anyone in the US that will touch it. Plus, by tuning the ECU you don't have to worry about the piggyback unit croaking out on you. It happens far more than you might realize. And when it goes, you're back to the stock map without even knowing it. It doesn't give you a warning sign, it just goes offline. The bike starts to run bad, and with significant changes to your motor, you'd run a good chance of causing significant damage due to very lean running.
So if your powercommander fails, the bike will still run? I've wondered about that. Good to know.
simon from south Australia
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NJ Mike

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Reply #13 on: November 25, 2022, 11:12:16 pm
So if your powercommander fails, the bike will still run? I've wondered about that. Good to know.

Like I said, it depends on how heavy the mods are. Will a stock ECU work with a cam and an 865 kit? We'll find out next week. It may work, but I wouldn't want to find out how long it takes to burn a hole in the top of the piston.
Been riding since 1980. Live in Bloomfield, NJ.

Current Ride: 2019 RE Conti GT 650

Past Rides: 2002 SV 650, 2001 Moto-Guzzi V11 Sport, 1985 BMW K75, 1992 Honda 750 Nighthawk, 1982 Yamaha Vision, 1981 Kawasaki GPZ 550, 1978 Honda 750F, 1980 Honda 650


gizzo

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Reply #14 on: November 25, 2022, 11:34:52 pm
Like I said, it depends on how heavy the mods are. Will a stock ECU work with a cam and an 865 kit? We'll find out next week. It may work, but I wouldn't want to find out how long it takes to burn a hole in the top of the piston.
Hmmmm. What I meant was does the engine continue to run with a failed pivgyback? It sounded like you were saying it will. Which is all I was asking. Because that's something I don't know.
 I'm well aware that an out of tune engine can damage itself, but that also it will still run with wildly out of spec tune.

I guess it's easiest if I just unplug my power commander while Th e engines running and see what happens.
simon from south Australia
Continental GT
Pantah
DR250
DRZ400SM
SL125