I started assembling my 340/S engine last night. My original pistons were in very good shape so I'm re-using them. When I tore the engine down I labeled the pistons for which cylinder they came from. PTO or Mag. When I cleaned them up I was very surprised not to find an arrow or dot on the piston top for direction placement. The 340/S Service Text book does not cover the engine rebuild. The SM-2100 Service Manual that covers piston ported rebuild tells you that the arrows point to the exhaust port side (front of the engine). The problem is the top ring land has the ring locating pin that will run dead center of the port opening. Either intake or exhaust?
The piston skirt aligns with the cylinder jug skirt best with the locating pin aimed at the intake port.
A NOS piston I have for regular 340 engine with a arrow indicated the top ring end gap goes to the intake side.
So which way does the top ring piston end gap go? Exhaust or Intake port side?
Looking for some verification.
Help
'72 400
'73 400, (2)500's, 600
'74 295/S (restored) 2010 HOF poker run survivor.
'75 800, JDX8,
'75 340/S 2011 & 2012 Vintage Challenge finisher.
'76 (2)400's
'78 Liquifire 340,440
'79 Spitfire
"If it has Tits, Tires, or Tracks it's gonna cost you money!"
The 340/S piston availabilty is nill to none. There are still some ring sets floating around. I felt very fortunate just to have two good pistons. A few guys here on the list have talked about having them repopped, but $$$$$$ is the issue.
I installed mine with the ring end gap toward the intake port. I would think the end gap in the exhaust port would create hot spots and possibly cause the ring to deteriorate.
'72 400
'73 400, (2)500's, 600
'74 295/S (restored) 2010 HOF poker run survivor.
'75 800, JDX8,
'75 340/S 2011 & 2012 Vintage Challenge finisher.
'76 (2)400's
'78 Liquifire 340,440
'79 Spitfire
"If it has Tits, Tires, or Tracks it's gonna cost you money!"
The intake port has a big tear drop in the center of it, that is so the ring doesn't catch the port, So because of this you can't even see both rings when @ BDC, the exhaust port will not have that tear drop so the ring would catch the port going to or from BDC..
I always mark the pistons with a scribed ( with a Ice pick ) arrow unless the pistons are plainly marked.
Also I personally believe that there is nothing wrong with used piston (as long as there is no cracks anyplace?? just clean them up using emery cloth or something like that.
( 2-strokes love clearance, used & sanded clean means clearance ) I would however hone the cyl.s & use NOS rings as there is an abundance of NOS 340/S & Dator rings out there..
Kenny
Last edited by ICCSF 108 on Sun Dec 14, 2008 8:24 pm, edited 1 time in total.
AKA: Kenny, Grumpy, Mr. Richard Head
"I Hunt For it, Purchase it, Haul it, Sometimes Repair it, Sometimes Break it, Then Fix it Again, Label it, Warehouse it, Talk About it, So NOW, HOW Can I Take Any Less $$ For It?"
"God I love the smell of KLOTZ in the morning, That smell, you know that Gasoline/Oil Smell, MAKES the whole place SMELL like.. LIKE VICTORY. You know someday the 2 strokers are gonna end..."
Do Anti-War Protesters have reunions? If so what do they TALK about?
Two stroke like clearance to a point, to much clearance and you get excessive piston slap, then your piston develops cracks in the skirt from the constant hammering. Finally the skirt breaks off, gets wadded into a ball in the bottom of your crankcase, probably destroying the cases. You'll also be very lucky if the crank comes away unscathed, generally the fragments of skirt, find there way into the lower end bearings.
I would never run a piston that is more than a few thousands of extra clearance.
Troy and I were disscussing this on the phone, and I had totally forgot about the dropped center in the intake port! Good point Kenny, that is why it is there Troy, problem solved.
Paul, we'd be putting in new pistons if we could find a truckload of them. Chuck has all the NOS ones.
'09 Vintage Challenge Survivor, and I wasn't late for supper!
'10, '11, '12, '13,'14,'15,'16,'17, '18, 19, 20, 21, 22 Vintage Challenge Survivor !
72 400 restored, Father bought new in '71
73 X8 restored
'74 340 green machine
'74 X8 9 time VC finisher
'78 Spitfire in progress
2 '75 340S 1 running, one on deck
'78 LF 440 future CC clone
'73 Skiroule RTX 440, 500 mi.
Speedy, Your Votech instructor never ran a Dator, some place on this site Jon has a post about how much clearance his Dator motor had, something about how you could hear the pistons clattering in the Cyl.s.. Stick around your bound to learn something on this site.. LOL
Kenny
Last edited by ICCSF 108 on Sun Dec 14, 2008 11:08 pm, edited 1 time in total.
AKA: Kenny, Grumpy, Mr. Richard Head
"I Hunt For it, Purchase it, Haul it, Sometimes Repair it, Sometimes Break it, Then Fix it Again, Label it, Warehouse it, Talk About it, So NOW, HOW Can I Take Any Less $$ For It?"
"God I love the smell of KLOTZ in the morning, That smell, you know that Gasoline/Oil Smell, MAKES the whole place SMELL like.. LIKE VICTORY. You know someday the 2 strokers are gonna end..."
Do Anti-War Protesters have reunions? If so what do they TALK about?
Good on Don, Paul, the only difference between the liquids & the air cooled ones is when working on the air cooled engines you not standing in a puddle of antifreeze
Kenny
Last edited by ICCSF 108 on Sun Dec 14, 2008 11:51 pm, edited 1 time in total.
AKA: Kenny, Grumpy, Mr. Richard Head
"I Hunt For it, Purchase it, Haul it, Sometimes Repair it, Sometimes Break it, Then Fix it Again, Label it, Warehouse it, Talk About it, So NOW, HOW Can I Take Any Less $$ For It?"
"God I love the smell of KLOTZ in the morning, That smell, you know that Gasoline/Oil Smell, MAKES the whole place SMELL like.. LIKE VICTORY. You know someday the 2 strokers are gonna end..."
Do Anti-War Protesters have reunions? If so what do they TALK about?
See you at the finish line Don in February...what is your drink of choice? I think I will have more than enough time to run in and get you a drink and have a couple for myself!!
I hope that trailer queen has got legs!! You better invest in legs instead of chrome!!
Last edited by Danzig on Mon Dec 15, 2008 12:43 am, edited 1 time in total.
ICCSF 108 wrote:Speedy, Your Votech instructor never ran a Dator, some place on this site Jon has a post about how much clearance his Dator motor had, something about how you could hear the pistons clattering in the Cyl.s.. Stick around your bound to learn something on this site.. LOL
Kenny
Votech? I don't have no instructor. I'm just saying I've seen this happen in dirtbikes frequently. Snowmobiles certainly are under much more abuse than a dirtbike, having a 8000RPM+ maintenance speed. I've been here for 3 years, I just get busy with cars, guitar, and dirtbike, so occasionly this place slips to the wayside. I have learned quite a bit on this site and intend on learning quite a bit more.
Good man, Dirt bikes do seem to swallow stuff that snowmobiles don't, that's why we normally only use empty air boxes & not filters.
Also 2-stroke cycles in general use a 3.0 Needle & Seat (gravity fed carbs no fuel pumps) so you might be able to run them on the ragged edge more often than sleds with a 1.5 or lower Needle & Seat & a pump...
Kenny
AKA: Kenny, Grumpy, Mr. Richard Head
"I Hunt For it, Purchase it, Haul it, Sometimes Repair it, Sometimes Break it, Then Fix it Again, Label it, Warehouse it, Talk About it, So NOW, HOW Can I Take Any Less $$ For It?"
"God I love the smell of KLOTZ in the morning, That smell, you know that Gasoline/Oil Smell, MAKES the whole place SMELL like.. LIKE VICTORY. You know someday the 2 strokers are gonna end..."
Do Anti-War Protesters have reunions? If so what do they TALK about?
With the cylinders installed you can see those tear drops in the intake ports and the pistons end gap placement makes perfect sense now.
You would be proud. I put a asterik beside the piston installation picture in my manual. Then in the notes page of the manual I added your comments about the reason for the tear drop in the intake.
Thanks
Troy
'72 400
'73 400, (2)500's, 600
'74 295/S (restored) 2010 HOF poker run survivor.
'75 800, JDX8,
'75 340/S 2011 & 2012 Vintage Challenge finisher.
'76 (2)400's
'78 Liquifire 340,440
'79 Spitfire
"If it has Tits, Tires, or Tracks it's gonna cost you money!"
Stick around your bound to learn something on this site.. 
