Compression test's and Piston's

[93 NSR]

I want to do a compression test on my mito, does anybody know what it should be?
Also i want to put a new piston in cos it's done 12500km and i'm not sure if its had a new piston. where can i get cheap / good pistons from. I've had a quote of £55 for one. when i asked what it was he said " a high grade jap piston "

Any thought's,
Craig

[Danny]

Right, you can buy a compression tester from Halfords or online, it's supposed to be 10 on an NSR so i'm assuming it's about the same for a mito.
I recomend you buy original parts if possible.

[Kickstart]

Hi

Nothing in the workshop manual listing the compression. However I would expect it to be around 140~150psi, maybe a bit higher.

All the best

Keith
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[Mr.Everready]

Do NSR's need new pistons after 9000 miles ?
A rather expensive job if your a high mileage guy.

[Danny]

No they don't afaik, atleast I hope not seeing as I own one

[cagiva gezzer]

Buy a cheap piston and cry. Well, thats what i did. The cheap ones are cast and crap. Much better to get the OE forged ones.

Cheapest place is MitoMondo at around £112 ish. You have to know what family you want though. 01425650034

Last time i tried in the summer mito mondo was the ONLY place in the UK to have OE pistons.

I tried two cast ones under the recommendation of the local dyno centre. First one did 3000km before it failed big style and caused a rebuild and replate. The second one did 2000km before i stripped it down and found that it was going the same way and i had to pay out for another replate to repair more damage.

The OE one did 16,000km and had only slight wear.

I think the difference is that the cast ones are softer and elongate their wrist pin holes which causes a nice rattle and bits of C clip to be removed and score/seize the topend.

Another prob is that the cast ones are usually flat top. This lowers compression and shoves the power up the rev range (compared to the domed ones) due to differences in port timing. Fine if you want that, but the piston cant cope.

Another prob is that because the cast ones are not as dense as the forged ones, they contain more material to be the same weight, and this extra material gets in the way of the ports and prevents cool air from getting around the cylinder. This causes over heating which doesnt help the wrist pin problem.

I also found that the cast ones have smaller windows = less small end cooling = MORE probs.

Cast pistons are also not as tight in the bore which causes excessive noise and wear and causes them to crack from the skirt to the window.

The above info is on a 2000 cagiva supercity, so it should be correct for the mito, but i think a mito might come with a single ring flat top as std.

Summary - Go for OE!


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"because one stroke isnt enough and four strokes waste two"