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General Category >> Rubber Side Down! >> 0.5 mm Over-sized Piston - Rejet??
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Message started by T-Mack1 on 07/30/07 at 10:05:10

Title: 0.5 mm Over-sized Piston - Rejet??
Post by T-Mack1 on 07/30/07 at 10:05:10

Does anyone have experience with the 0.5 mm oversized pistons???

Do I need to rejet the carb??? I've done the white space mod (took two tries to get washers that would fit into the depression in the slide). I have the brass plug out and ready for when the engine is back together. I'm still in the process of cleaning the internal parts. I guess I should post of pict of the insides for everyone to see, not much there.

Bike is a 2001 and looks to be 100% stock when I picked it up. Other than the engine was in pieces and the piston looked like s--t (Melted and flaking on the trailing side). Bike has 10460 miles.

I'm planning to keep the pipes and air cleaner stock to start with. The exhaust pipe has almost no blueing and the muffler is slightly discolored at the back.

I did the volume calcuations and it's going fm a 652cc to a 659cc displacement. That's just over 1% larger.

I would be grateful for any shared knowledge. A from/to jet size would be good if you've already did the O.S. piston.

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by Bugscraper on 07/31/07 at 18:16:37

Just curious why you didn't bump it up to 700cc's while you were at it?

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by jd06s40 on 07/31/07 at 18:30:59

is there a big bore kit with piston,rod,cylinder,etc for the savage/s40 650 available

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by LANCER on 07/31/07 at 18:50:07

Pistons available in 95, 96 & 97mm overbore, then just have the cylinder bored at a machine shop, use same rod.

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by jd06s40 on 07/31/07 at 19:27:35

what would that 97 take the cc to

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by klx650sm2002 on 08/01/07 at 02:36:02

A 97mm piston would give 694cc.

Clive W :D

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by T-Mack1 on 08/01/07 at 06:36:28

Bugscraper,
Didn't bump up to 700CC this time because I'm from old school where we try to repair things over & over again. In another 20 to 30K miles I'll go one more step up, then after that another , and another.

Hey, here's a idea, why not do like they do to the Honda 50cc's. New jug & head assy's that increases the size of the engine. On those, the case opening has to be machined to fit the bigger sleeve. Can you see a Savage with a 1000cc or even a 1200cc engine......probably would need a safety harness just to hold you on to the bike during accelerations. Wonder how long the tranny could handle it?

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by Savage_Rob on 08/01/07 at 09:45:44

I think I'd be concerned about the effect of increasing displacement too much without modifying the counterbalancer. Doesn't that seem logical?

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by srinath on 08/01/07 at 11:02:54

LANCER wrote:

Pistons available in 95, 96 & 97mm overbore, then just have the cylinder bored at a machine shop, use same rod.

Yes ... however that is only 1/2 true ... those are DR650 pistons ... ;D and oh yea, they'd fit and work and be super cool, however they are much lighter and stronger and have these tiny skirts and I believe they have piston pins that sit too close to the rings. Wonder if they would lower the compression,
Also a lot of like 400CC atv's have huge pistons and they also are super light and have pins that sit 1/2 way in the bores.
Cool.
Srinath.

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by T-Mack1 on 08/02/07 at 06:37:17

So, now that my what if made you think, let's get back to the thread.

Rejet the Card for the factory 0.5 mm O.S. pistion (94.5mm)??????????????

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by vroom1776 on 08/02/07 at 10:46:27

start rich and work your way down.

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by T-Mack1 on 08/17/07 at 13:59:55

So, contiuing from the gas mileage thread:

First: Thanks go out to Lancer for selling me jets.

Today, was off (have to use up vacation days or lose them).

Took out the factory 145 jet (2001). (had to take battery housing off, means seat too). Put in the 150. Then, what's that noise,......thunder.....turn on radio and hear severe T-Storm warning and tornado warning for neighboring county 20 miles away. Tornado's in PA.......Da_mn.....

Well, start bike & play with air screw, was 1 1/2 turn to lean roughness, 1 turn to rich roughness. Could explain the carbon on sides of spark plug ceramic. Turn down 1/2 turn. Turn off bike, go eat lunch. Come out and start bike, hey need one click of choke, might be a sign that was too rich before (carbon on spark plug).

Sun is out and roads dry. Roll out of garage and see dark clouds coming. Quick trip around the big block (about 1 1/2 miles). Runs a bit better.

Home again, come in to check forun, see Lancers suggestion to put in the 155 first, D-amn, off comes seat & battery housing. 155 in, ten minutes, wow, getting better at this. Roll out of garage, more dark clouds, but will try. Get 1/4 mile and it starts raining, but.....no bogging down, ...hmmm. Get home and here I am waiting for the roads to dry again. Want to get to the highway for some 55 MPH driving.

Lancer, again, thanks for the help......

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by LANCER on 08/17/07 at 15:18:39

Happy to do anything I can.

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by T-Mack1 on 08/17/07 at 18:07:12

Did a 15 mile run. Bike runs good, smoother and more power/torque. No bogging down what so ever.

When I got home, let engine cool down.....check plug. Looks ok. Yea........will check again in a week or so.

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by Savage_Rob on 08/18/07 at 07:25:45

Savage_Rob wrote:

I think I'd be concerned about the effect of increasing displacement too much without modifying the counterbalancer. Doesn't that seem logical?

I didn't see any thoughts on this. I don't know if everyone just thought it was a stupid question or if they were studiously avoiding the topic. I mean, on a multi-cylinder engine it's less of an issue and it's virtually a non-issue as long as opposing cylinders are enlarged at the same time but I'm thinking the counterbalancer is designed with the stock displacement in mind. While it may be that small increases in displacement won't make an appreciable difference, wouldn't it follow that the engine would become less stable the more you alter the displacement?

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by LANCER on 08/18/07 at 14:30:58

Savage_Rob wrote:

Wouldn't the only real concern be if the replacement piston is the same weight as the stock piston?

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by Trippah on 08/18/07 at 16:11:56

would counterblancing be concerned with weight (of the piston) or mass? And functionally what would be the difference?

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by LANCER on 08/18/07 at 18:19:14

I think so. It is called a "counter-balancer", and that implies weight or mass is being compensated for.

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by Savage_Rob on 08/19/07 at 13:30:22

Maybe my emphasizing the word "displacement" was a poor choice in phrasing but I think the result is basically the same - a larger cylinder, with a larger piston inside it... and I'm thinking that most of the time a larger piston would have greater mass - assuming similar materials are used and it's shaped generally the same as the original. So now back to my question. Does this represent an appreciable difference in mass to which the issue of counterbalance should be addressed?

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by LANCER on 08/19/07 at 15:07:56

The Wiseco pistons do not list the weight, but they are forged pistons.
The Sudco book lists a 100mm forged piston for the DR650 at 375 grams.
The piston from my engine is roughly 405-410 grams (the scale is not perfectly accurate and could easily be +/- 5% ), which is 35 grams, or about 7% +/-weight difference.
That seems like a significant amount.

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by T-Mack1 on 08/19/07 at 20:51:01

First, you could reduce weight by making a billet connecting rod. Vertical moving weight would be less. Would need some thinking on which alloy would be stong enough.

Second, Went for a 40 mile ride yesterday, back rode and freeway driving ( found out they re-grooved about a mile of the expressway not too long ago (I-78). Well, at the end of the trip about a half mile from home, it started to buck a little. Got home and checked the spark plug. Solid black.

Apart it comes again. .........

Title: Re: 0.5 mm Over-sized Piston - Rejet??
Post by LANCER on 08/20/07 at 04:23:34

Will the larger but slightly lighter in weight piston really cause any problem? I think it would be a better situation.