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Top end/high compression piston question

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I have an 06 drz400sm , 3X3, Yosh rs3 full pipe, K&N , fcr39 carb. The bike has 20K miles, no issues. I decided to take it to my mechanic and get a top end done just because it has 20K, I figure it's time. Is it a reasonable assumption that need that(top end)?

I don't want to go with the big bore kit because of $$ and I like my current MPG.

My question is that if I change the piston is it worth to put a high compression piston? will I gain performance from it, any reliability issues?

thanks:ride:

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You will not gain much. I would go stock size and put it all back. If you gonna upgrade you want to probably get 1 piece valves when your doing the top end.

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only real way to determine top end condition is to take it apart & measure everything to the specs in the manual.

once you have it apart, you need a gasket set, rings & circlips anyway.

if you want to bump up compression, just use a single layer base gasket for 12:1 compression.

any more compression & high octane pump gas won't cut it.

there's also the condition of the valves to consider.

are you burning oil or down on power?

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if you want to bump up compression, just use a single layer base gasket for 12:1 compression.

any more compression & high octane pump gas won't cut it.

?

I have to disagree with the gas comment.....I was running a 95.5 mm cyl and13.5:1 compression JE piston and had no problem with high octane pump gas......I did however have continual sealing issues and coolant ending up in the oil....Went through 2 kits with the same result. All went away when I dropped down to a 94 mm kit and single layer base gasket. I should've listened to Eddie sooner:bonk:

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only real way to determine top end condition is to take it apart & measure everything to the specs in the manual.

once you have it apart, you need a gasket set, rings & circlips anyway.

if you want to bump up compression, just use a single layer base gasket for 12:1 compression.

any more compression & high octane pump gas won't cut it.

there's also the condition of the valves to consider.

are you burning oil or down on power?

Not burning oil, great on power.

Yes, it's comming apart to assess.

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You will not gain much. I would go stock size and put it all back. If you gonna upgrade you want to probably get 1 piece valves when your doing the top end.

thanks:thumbsup:

what will the one piece valve gets me?

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Thanks guys, so to summarize the opinions:

-No on high compression piston.:confused:

-Change to one piece valves.:thumbsup:

Anything else while it’s all open?

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Valves springs , get the RHC kit , it has all you need :thumbsup:

And don't forget the single layer base gasket !

Cool,

Does the single layer base gasket changes the compression?

Confused about the compression: the stock is 11.3:1 and 90mm.

The after market kits for 90mm are either 12.2:1(Standard Comp) or 13.5:1(High Compression).

So even if I go with an aftermarket kit standard I am still increasing the compression, right?

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bumped for this question:

Confused about the compression: the stock is 11.3:1 and 90mm.

The after market kits for 90mm are either 12.2:1(Standard Comp) or 13.5:1(High Compression).

So even if I go with an aftermarket kit standard I am still increasing the compression, right?

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If you just want to bump to 12-1 all you have to do is pop the rivets in the base gasket of the standard kit and use either top or bottom ply. Really don't think the 94 mm kit will compromise either reliability or fuel consumption.

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I don't understand why people take a bike that is running perfectly and decide to tear it apart and rebuild it "just because". Your wasting money and taking the risk that the guy who does the work is not going to screw up a perfectly good running bike and cost you even more money. (Has happened many times to guys here who have taken bikes to so-called professionals.) There is only 1 professional I would trust my DRZ to...and also a few experienced amatuers who post here.

Other than that...if I can't do it myself...it will not be done.

If it ain't broke...don't fix it...unless you are upgrading for more power. Leave it alone.

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I don't understand why people take a bike that is running perfectly and decide to tear it apart and rebuild it "just because". Your wasting money and taking the risk that the guy who does the work is not going to screw up a perfectly good running bike and cost you even more money. (Has happened many times to guys here who have taken bikes to so-called professionals.) There is only 1 professional I would trust my DRZ to...and also a few experienced amatuers who post here.

Other than that...if I can't do it myself...it will not be done.

If it ain't broke...don't fix it...unless you are upgrading for more power. Leave it alone.

Good point, that was part of my original questions. Do I really need to do it? I guess your answer is a big no. I am just surprised no one else had the same impression.

I decided to do it as a “preventative maintenance”. The question is once things start to go will be warning signs or just things start to brake.

At this point my mechanic is taking the top off and see how things are. Let see what he comes back.

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20k miles really isnt that much ridden on the road only. go for another 20k and see how it goes.

I know someone here who has 40k miles without a rebuild and runs like a top.

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Good point, that was part of my original questions. Do I really need to do it? I guess your answer is a big no. I am just surprised no one else had the same impression.

that's why i asked if it used oil or was low on power.

also, the bottom end has just as much mileage as the top end. and i've seen the bottom end go before the top end twice now.

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No such think as a preventative rebuild. You either need one or you don't. Wait until you have an obvious problem before disecting your engine...and you should be using good diagnostic methods before doing that.

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OK, thanks for all the input :thumbsup:.

As for now I will hold off the preventative:smirk:-top-end rebuild.

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