Heavy pistons

Hi Guys

Need some advise from some of your knowleged people balance.
3 years ago i put some new pistons in my 850 commando, I did not drive much before i changed the pistons so i did not have too much feeling of how much the engine vibrated, I have tried to adjust the isos because i felt I had to much vibrations but it did not seems to make any difference. I always had a feeling that the new pistons was heavier than the old ones só today I took the engine apart.
I still had the old pistons in the workshop so I put them on a digital kitchen scale 1 weighs 399grams the new ones also standars bore size weighs 442grams :?:
Old ones AE new ones JP.
What are your thoughts about that?
Does these ekstra 43grams make my engine shake like a "air hammer"

Best Regards

Henrik

That's 80+ grams (both pistons)

That'll make a difference alright...

Yes, thats also my feeling.
anyone having a guess what change in balance factor that makes?

These where bought at the norvil motorcycle compagny in the U.K. I think he should have known better than selling crap like that :evil:

I am feeling very dissapointed right now.

Best Regards

Henrik

Lucky said:

Yes, thats also my feeling.
anyone having a guess what change in balance factor that makes?

These where bought at the norvil motorcycle compagny in the U.K. I think he should have known better than selling crap like that :evil:

I am feeling very dissapointed right now.

Best Regards

Henrik

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It's not necessarily crap. It's worse when the two pistons don't match.

Do you tell him what brand you had originally?

Those pistons are way too heavy. You can use high quality pistons that weigh only 215 grams and your 850 will ride smoother than ever.

Details about lightweight pistons as shown below are at:

http://users.gotsky.com/jimschmidt/nortonrods.html

jseng1 said:

Those pistons are way too heavy. You can use high quality pistons that weigh only 215 grams and your 850 will ride smoother than ever.

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While the lust factor is super high on these you do need to purchase the rods too. So it's well over $1000 for the whole set up.

You can get into a stock pair of pistons for something around $300. Which is important if you don't want to get into the bottom end.

Yes, these really look great, but as you said, when the bottom is disassembled you want new main etc. etc.
and as I live in Denmark i have to pay 25% tax of the parts + shipping from the US, so it will be quite expensive and spring is very close here
I think I will go for some AE hepolite from RGM.
What pistons do you guys use?

Regards

Henrik

Lucky said:

Yes, these really look great, but as you said, when the bottom is disassembled you want new main etc. etc.

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What would be really cool is lightweight pistons that fit on the standard rods.

Actually I have been looking for that the last hours but with no luck.

Lucky said:

Actually I have been looking for that the last hours but with no luck.

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Don't bother. Super lightwieght like what Jim offers isn't available, and may never be. The short deck requires the new rods.

I am still running Omega high compression piston, these are heavier than standard pistons. No ill effects from vibration at all.

Henrik,
When you first built the top end, did you pay very careful attention to setting up the top head steady? This can create roughness if not done properly. In addition, if you do not already have it, I would recommend you fit the Mk3 spring kit to the headsteady. This certainly assists the Isos. It may well be that the heavier pistons are manageable if you optimise the Isos.

Mick

Hello Henrik
Seeing that your engine is apart and you have taken the pistons out. You can bring your Crankshaft, Con Rods, Pistons/ wrist pins and Rings to a Balance Shop and have the Balance Factor Changed to suit your new piston weight. Harmonic and Dynamic balance the Crank would cost you a lot less than going for new pistons. I have my Combat Crank balanced by Forest and Forest. Herb Becker recommended these guys in my area. You have to search around Denmark. (That’s your homework. If there is nobody you can trust there then try England). I put on +0.020 GPM pistons and they are a lot heavier than the equivalent Hepolite Pistons in the same Overbore size. Swoohdave is right Not Necessarily Crap.
Balance Factor for an 850 should be 52% Dry. Please correct me if I am wrong but I took it from the Norton Tech Digest 3. A filled up Sludge Trap can change the balance factor by 10-12 %. When you changed for the new pistons did you split the crankshaft? If no, then buy new Crank stud and nut kit 06-4184 if you want to make sure the sludge trap is not filled. If you go this route then before you split the crankshaft pin punch a mark on the timing side cheek and on the same side of the flywheel to make sure you do not put it together the wrong way around. 8)
Regards,
CNN

Lucky said:

Yes, thats also my feeling.
anyone having a guess what change in balance factor that makes?

These where bought at the norvil motorcycle compagny in the U.K. I think he should have known better than selling crap like that :evil:

I am feeling very dissapointed right now.

Best Regards

Henrik

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With a balance factor of 52%, you would need about 45 grams added to the flywheels to make those heavier pistons balance the same as the lighter ones.

Hi all

Thanks for your replys.

The thing is that I only have the head and barrels of, the engine runs ok and I dont have any problems with the bottom end, but I know if I start on the bottom end I cant assemble it again without regrind of the cranck, new big ends, mains a PW3 cam etc. and I do not feel this is nessesary at the moment.
So I was hoping just putting a pair of new original AE Hepolite pistons would save me from the above?

I have a dave Taylor head steady with the MK3 spring, but adjusting did not seems to help,
the worst spot was a few hundred rews above tickover, there the engine literaly "jumps" up and down.

Regards
Henrik

I wouldn't rebalance a crank for heavy pistons, it will end up looking like swiss cheese when you next rebalance for the correct weight pistons on the next rebore. Go for the hepolites which were the orginal fitment.

Lucky, is there enough meat on the pistons, under the crowns for example, where you could remove some of the weight yourself and bring the pistons down to something nearer the original weight? This should be relatively straight forward with a Dremel grinder and you might be able to solve the problem in a couple of hours at home.

Had the thought of removing material, but had no feeling of how much can be done without risking the piston to fail, which eventually could end up beeing very expensive and dangerous if the engine lock.
I think the Hepolites is the correct decision in this case.

Thanks for all the comments

Best Regards

Henrik

swooshdave said:

Lucky said:

Yes, these really look great, but as you said, when the bottom is disassembled you want new main etc. etc.

Click to expand...

What would be really cool is lightweight pistons that fit on the standard rods.

Click to expand...

Steve Maney!!!!!

Lucky said:

Had the thought of removing material, but had no feeling of how much can be done without risking the piston to fail, which eventually could end up beeing very expensive and dangerous if the engine lock. I think the Hepolites is the correct decision in this case. Thanks for all the comments

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There's a smart lad.