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March 29th, 2008, 09:43 AM   #1
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high compression piston.

It's been said that the 450 piston will give you an upped compression on the 550 and 650 how do I know what I have, the piston crown in mine is perfectly flat, is the 450 slightly raised.
I was looking at the workshop manual nothing in particular and just happened to see on the page where they fit the piston the piston crown is concaved hence my question.

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Sparks.
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March 29th, 2008, 10:02 AM   #2
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2007 450 has a dome type piston.Distance from top of the wrist pin to the top of the piston is 14,4mm + ~3mm dome.
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March 30th, 2008, 12:35 PM   #3
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it's said that the 470 piston gives higher comp steve?

as swedish steel said recently though: the newer pistons are far lighter than the old stuff and this is more important.

first task should be to get the squish right. try to get .035" to .040"

regards

taffy
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March 31st, 2008, 05:05 AM   #4
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It depends on the year sparks.

In 04 the 650 piston went concave, previously it was flat (I don't know about the current 628 variety). Up until then the high comp mod was to use the 470 piston which had a wicked ramp (angular rather than smooth) or a couple of other aftermarket makers.

As fourstrokeforce says, in 07 the 450 has a dome.

It gets confusing and difficult to follow.....

All the best,
Simon
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April 1st, 2008, 12:32 AM   #5
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Originally Posted by Simon
It depends on the year sparks.

In 04 the 650 piston went concave, previously it was flat (I don't know about the current 628 variety). Up until then the high comp mod was to use the 470 piston which had a wicked ramp (angular rather than smooth) or a couple of other aftermarket makers.

As fourstrokeforce says, in 07 the 450 has a dome.

It gets confusing and difficult to follow.....

All the best,
Simon
Thanks for that mine is a 550 04 which had just had a new piston and crank when I got it, but with seeing the photo in the manual that showed a dished crown I was wondering if mine should be the same and the flat top piston which is now fitted has made it higher compression.

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Sparks.
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April 6th, 2008, 11:31 PM   #6
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first task should be to get the squish right. try to get .035" to .040"


taffy,
i understand now how enginehardware got his squish right(with the 670cc stroker crank)
being 3mm longer(1.5mm futher down+1.5mm futher up).

now, how do get the squish right using a std crank and rod.
like we have been saying hi comp pistons reduce the squish but bad cause they weigh so much.gain performance one way lose in another.
..weed..
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April 7th, 2008, 01:29 AM   #7
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As the cam chain tension is VERY sensitive to any adjustments on deck height, gasket thickness or cylinder head height, things are pointing in the direction of having your own special piston produced. I, for myself, had to go there because of my large valves and valve lift. To get low weight, and strong design, it is crucial to find a manufacturer with a good 100mm forging. The Wössner pistons are still too heavy in my opinion. Still looking.. Any tips would be appreciated! I have designed a complete piston in 3D CAD, but I shouldn´t have to make my own pistons as well, do I?
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April 7th, 2008, 10:23 AM   #8
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Originally Posted by popup
first task should be to get the squish right. try to get .035" to .040"


taffy,
i understand now how enginehardware got his squish right(with the 670cc stroker crank)
being 3mm longer(1.5mm futher down+1.5mm futher up).

now, how do get the squish right using a std crank and rod.
like we have been saying hi comp pistons reduce the squish but bad cause they weigh so much.gain performance one way lose in another.
..weed..
i have no doubt IMHO. you must either increase the length of the rod to 136-137mm or as i used to do - lop the correct amount off the top of the cases and spigot although as you know, i have a slightly 'proud' spigot for better cylinder sealing.

there is a thin gasket available in the doc to help but i would save that for after machining work so you could bring the piston to had nearer if it's available.

one piston or another won't vary even a thou from the same manufacturer but the different makers may well be all over the show!

by machining the barrel you aren't changing the balance or adding any weight.

your next problem is the camchain. the camgear teeth won't line up! they will be 2mm out as measured at the outer circumference of the gear.

you can slot the gear for this. there is more than enough meat for this. careful study of the doc will also show that moving of gear teeth in the primary drive one way whilst 'reversing' this with the cam gear will bring you close.

BTW, if anyone has a 100mm piston (new) about i need one.

regards

Taffy
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April 7th, 2008, 04:02 PM   #9
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i don't know what the piston squish is on the 450/550 but like i said on my old 650 , the piston comes up 2mm below deck height + the 1.4mm head gasket =3.4mm squish.with these specs
the book says my compression ratio is 12.2:1
for instance if i adjusted my squish to .040" or 1mm (2.4mm off what i got now) i recon i would have to be at great risk of detonation, would't i ?
the way i see i is ,the only way you could run a 1mm squish, is with a cam with heaps of overlap like a x1 or a crate engine cam.tell me if i'm wromg?

dr c , enginehardware was telling us that elko pistons are the lightest.

taffy,i see how you readjust cam timing,but you only have to skim 1/2 a fly poo off deck height and your cam chain will have no adjustment.
whatever you take off deck height ,you have to fill on the bottom of the cam bearings,then machine out the same amount in the rocker cover.
..weed..
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April 7th, 2008, 11:05 PM   #10
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i don't think it's as bad as you say popup? if you are bringing camchain adjustment into this i suggest you try a little experomenting.

remember that the very early 400s (and maybe others?) had a 1" alloy knob on the end. then they went to a shorter one and then they got rid of them completely.

i believe i still have a photo of my early tensioner in my gallery and the doc. the alloy knowb was very long.

regards

Taffy
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