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Johnny Two Tone
'15 GTS300, '86 PX125EFL, '66 VBB, '01 ET4
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Does the ET3 top end use the same cylinder head as the earlier primavera engine?

I'm assuming I can drop an ET3 cylinder on my stock lump, re-use the cylinder head, polini kidney, and 19mm carb. Probably have to drop the timing back to 20 degrees like ET3 used? Is that it?

Scooterworks has the kits on Ebay for ridiculous prices, with free shipping. I figured it was too cheap not to have a look.

-John
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I have these pics for reference.

Ive used both stock head and primavera.

Always check squish.
Forum member supplied image with no explanatory text
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John,

Just toss that barrel on. Using same piston?

You'll have to do your timing over and such; TDC may change due to different piston.
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Johnny Two Tone
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I was assuming using the new piston, I have no idea what is in my Primavera cylinder.

Time it like an ET 3 or a primmy? I wasn't sure. I figured ET 3 20 degrees.
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sdjohn wrote:
I was assuming using the new piston, I have no idea what is in my Primavera cylinder.

Time it like an ET 3 or a primmy? I wasn't sure. I figured ET 3 20 degrees.
Yes, like an ET3. Do you have an ET3 primary set? If so, you should move on that. I've got a few stashed away.
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Chris is better at this shit than I am but I have a question.

Did you ask marcus if he ever oversized the piston. Hes had it a loooong time and so you should measure your piston or unfortunately you have to order a new piston to go with the barrel. If it a stock piston than it should be fine witht he new barrel and your old head.

Get it.....old head!!! Im f'n funnee dude
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Johnny Two Tone
'15 GTS300, '86 PX125EFL, '66 VBB, '01 ET4
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Barrel comes with a new piston too:)
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sdjohn wrote:
Barrel comes with a new piston too:)
There ya go. Done and done. Check the champer and squish.
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Johnny Two Tone
'15 GTS300, '86 PX125EFL, '66 VBB, '01 ET4
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Chris theET3 had different primaries?
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sdjohn wrote:
Chris theET3 had different primaries?
If hes not gonna answer you I will.

Yes.

there in the 20something/60 soething.

The gear stack/cassette is the same but the primarys vary from bikes. The et3 sahares the same as others and the primmy shares the same with others.

Maybe chris knows exactly the primary numbers.

But I wouldn't worry about that shit right now. Youre looking for more oomph for a hill the barrel swap will be a good start.
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An et3 and primavera have the same primary ratio: 24/61 helical cut gears (2.54).

The et3 cylinder head has a slightly different head over a stock primavera. The et3 head looks like pic #1 in Jimmy's photos, its very similar to a polini style. It has a wider squish band and smaller combustion chamber over a stock primavera. I would think it has a slightly higher compression ratio. Photo #2 & #3 are primmy style heads.

Timing on et3 is 20º and primavera is 24º.
Forum member supplied image with no explanatory text
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Johnny Two Tone
'15 GTS300, '86 PX125EFL, '66 VBB, '01 ET4
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Now that makes sense - the higher compression ratio is the reason for the timing change. 8.2:1 vs. 9.25:1
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