Piston parts

[DewCatTea-Bob]

____ Well so-far the only stockpile of pistons I've been able to locate, is just my stash of used-pistons.
As many of them as I have, I had thought sure I'd have at-least one 74.4mm,, but aside from a couple of 74.6 and 74.8 & 75mm sizes, all the rest were std.74mm (which actually measured between 2.906 to 2.907" *).
The piston-size closet to your requested size actually measures at 2.932", (which is near .005" under 74.6mm and .003" larger than your stated target size),, whilst I was searching for a 250-piston with an OD of 2.922 to 2.925". - (* It ought be apparent that the pistons are actually sized according to the intended bore-size of the cylinder-liner rather than the diameter of the piston itself.)
So a 74.6-size may work close-enough for you, if you wish to stick with a used-piston. (?)


Sorry-Cheers,
-Bob

[single-junk]

Thanks for looking into it Bob.. much appreciated.

With a 74.6 piston, I could get my 2nd cylinder honed/cleaned up (it measured in at 74.59 with slight corrosion) and it should work perfectly for that correct?
Provided I could get a set of rings for it from you as well..

[DewCatTea-Bob]

[quote= single-junk ...
" With a 74.6 piston, I could get my 2nd cylinder honed/cleaned up (it measured in at 74.59 with slight corrosion) and it should work perfectly for that correct? "

____ Can't say for-sure that the final end-result would be absolutely 'perfect',, but it's pretty certain that it'd be quite close enough, (considering the intended piston is a used-one anyhow).
A light hone-job should remove "slight corrosion" without taking the cyl.bore notably past 74.60mm, so it seems we have a good match-up.



" Provided I could get a set of rings for it from you "

____ I have lots of NOS ring-sets of most-all sizes (except standard) left !
__ My used 74.6-pistons are both 4-ring Monza types which use a pair of 2mm comp.rings and a pair of 2.5mm oil-rings, however my new Monza-type ring-sets only include just one oil-ring,, so either the piston's bottom ring-slot could be left empty or-else fitted with a used oil-ring of either the correct dia.size or any smaller size. - (A smaller/std.size could do the job since the ring end-gap clearance is-not important with oil-rings, [especially-so at the bottom location].)


Duke-Cheers,
-Bob

[single-junk]

Am I safe to assume then that it's ok to run it without the bottom ring?

Though I would get one if I knew they were readily available somewhere.. are they possible to buy as a single part? Or would it generally only be included in an entire ring set?

[DewCatTea-Bob]

[quote= single-junk ...
" Am I safe to assume then that it's ok to run it without the bottom ring? "

____ Not-only just that, but it was once considered to be a worthy performance-advantage to cut-off the lower-skirt of the piston right-at the lower ring-grove to not-only ditch that unnecessary oil-ring (and it's contributed friction), but-also the entire lower section of the piston-skirt,, for the main-purpose of significantly lightening-up the piston and-thus also reduce it's burden of being accelerated by the engine-power, (and-also to reduce engine-vibration as well) ! _ At-least that was the expectations of those who bothered with doing that somewhat popular radical piston-mod.
While I-myself was once only tempted to try the same,, I've never actually gone-ahead & performed that entire piston-mod from scratch for any of my-own engines, but have found 250-Monza & Motocross/Scrambler engines, (mostly the later !) with such modified (4-ring type) pistons. _ Of-which, I replaced,, and, after completing an improved finish-job* to the previously-done piston-skirt mod.work (* so that the modified p.skirt looked more like factory-work than a hack-sawed butcher-job),, I then traded-off those pistons to those more inclined to make use of them.
__ I've ridden with so-equipped engines,, and while I didn't really notice any marked improvement in acceleration-performance, I did think I noticed that the engine-vibration was sort-of different and not really improved overall.
So I-myself never recommended that piston-mod, but rather only told others of it being recommended* by racer-types, (* along-with lightened crankshafts, etc.).



" are they possible to buy as a single part? Or would it generally only be included in an entire ring set? "

____ Normally, ya can only get any particular p.ring by purchasing an entire set,, but it's been possible to find sellers (like myself) with ring-sets which have already been robbed and may still possibly retain the ring sought-after.
__ If you really desire, I will give you a used std.size oil-ring to fill the bottom ring-slot, (but the used-rings I have aren't pretty and-thus would require some cleaning, [as most of the used-pistons do as well] ).


Dukaddy-DUKEs,
-Bob

[single-junk]

Bob, I sent you an email at your new address.

[DewCatTea-Bob]

Bob, I sent you an email at your new address.

____ And I've found it, and sent a reply back to you.


Cheers 2U,
-Bob

[single-junk]

Bob, sent you another email.

[DewCatTea-Bob]

Bob, sent you another email.

____ I've been aware of that but, that email-account is ad.supported and it seems that when some recently included new ad.pop-up tries to get fully loaded-up & run, the process then causes my browser to crash before I can look-over my email. - (I guess I need to install more ram in this PC, as it's hard-drive runs like mad just before the crash-events.)
I've assumed the offending ad will get fixed or replaced before too long and I'll then get-around to sending you a reply-email.

____ To make this post somewhat more worthy of being posted, I'll add mention of having just two NOS.Mondial-pistons left in stock - (one 74.6 & one 75mm), both of which are 10:1-cr.versions intended for 250Mark-III (not 'Mark-3') engines.
And on the other-hand,, also have-left a half-dozen 75mm ASSO 8:1-cr.versions rather with the larger-sized valve-pockets, (as apparently Asso intended universal fitment within any 250 engine-model).


Hopeful-Cheers,
-Bob

[single-junk]

Bob, sent you another email.

____ I've been aware of that but, that email-account is ad.supported and it seems that when some recently included new ad.pop-up tries to get fully loaded-up & run, the process then causes my browser to crash before I can look-over my email. - (I guess I need to install more ram in this PC, as it's hard-drive runs like mad just before the crash-events.)
I've assumed the offending ad will get fixed or replaced before too long and I'll then get-around to sending you a reply-email.

Sounds like you need to install Firefox with Adblock.. problem solved.

____ To make this post somewhat more worthy of being posted, I'll add mention of having just two NOS.Mondial-pistons left in stock - (one 74.6 & one 75mm), both of which are 10:1-cr.versions intended for 250Mark-III (not 'Mark-3') engines.
And on the other-hand,, also have-left a half-dozen 75mm ASSO 8:1-cr.versions rather with the larger-sized valve-pockets, (as apparently Asso intended universal fitment within any 250 engine-model).

Hopeful-Cheers,
-Bob

I'm not up to snuff on compression ratios on Dukes yet.. does the larger compression number mean larger valves required?