76.44 mm piston what CC's

[yellowbeard]

hey guys, what kind of cc's are we talking about? from what I've read a 250r with big bore kit is 72.00 mm, makes it a 295 cc. Is this right? So what is a 77.44 mm? thanks Joe

[cr480r]

what year R? 77.44mm Bore? or 76.44mm bore? your post includes both....

[cr480r]

An air cooled is 295.3cc with 76.44 bore.... a water pumper is 330cc with that same bore

[1upfront]

You have to include the stroke of the engine into the equation.The aircooler stock has a 64.4mm stroke and a 70mm piston it takes a 76mm piston to get 300cc out of the motor without stroking the crank. The 85 R had a 66.0mm bore and a 72mm stroke so therefore you may get a 295 out of that with a 72mm piston.

[yellowbeard]

sorry guys, it's early, it's a 84 250r with a big bore kit. with a 76.44 mm piston.

[Bryan Raffa]

sorry guys, it's early, it's a 84 250r with a big bore kit. with a 76.44 mm piston.

so you didnt know you had a 300 kit huh.. that like getting a present right there..good luck on it .. these guys will point you in the right direction!

it would be better for you and us if you could keep all your post's in one thred;)

[yellowbeard]

will do, just i'm new to dealing with the big bore kit. will try to keep my questions to a min. and all in one thread. real interesting, thanks for the info. Joe

[Bryan Raffa]

NO NO Please ask your question's these guys will answer!!:welcome:

[cr480r]

will try to keep my questions to a min. and all in one thread.

Questions are good... post as many Q's as you want...I think what Raffa means is try not to post multiple threads on similar topics and search to see if a topic has already be covered before starting a new one... Old threads can easily be revived by adding a new question that relates to the topic..

[Yamahondaman]

I Think SYKO has some info on the Air Cooled Thing's as well .. Raffa .. you have one of those ATC's also ?

[Bryan Raffa]

Nope.. I built one for Bruce's ice racer...Mr hondaline had the parts on the shelf for his particular build..I really hope to see it on the ice this year..

[scrawny]

yep you are right, 295.3907 etc.....

[yellowbeard]

hey guys, 1upfront has it posted ^ that 72mm = 295cc. what I'm looking at is 76.44. So, if 72mm is 295cc what is 76.44? Joe

[yellowbeard]

ok re-read cr480's post said that 76.44 is 295cc. been reading up on all the old threads about the big bore kit. still have no idea what ya'll mean by decking the cylinder. my cylinder, shouldn't it be already decked since it has had a 76.44 mm piston already.

[cr480r]

Well by the sounds of it the new replacement piston is a bit different from the original... So even though the bore size is the same as your old piston, the piston height is not... The deck height is the distance from the top to the bottom of the cylinder... So since the distance from the piston pin to the top of the new piston is reduced the cylinder deck height would need to be reduced the same amount for the piston to reach the top of the bore at tdc again.

[yellowbeard]

have not ordered new piston yet, I'm going to mike the cylinder and see what I have. the 76.44 is the piston that was in it. the old piston seems tight in the cylinder. they sell 76.44. what is the clearence between piston and cylinder wall. still not sure about decking.

[cr480r]

usually about .003" for a forged piston, cast pistons can run a lil tighter .002-.0025"

[1upfront]

have not ordered new piston yet, I'm going to mike the cylinder and see what I have. the 76.44 is the piston that was in it. the old piston seems tight in the cylinder. they sell 76.44. what is the clearence between piston and cylinder wall. still not sure about decking.

Decking is where the stand your cylinder up on a machine and it comes along and shaves the top of the cylinder down. This will need to be done if you use one of those wiseco's. The guy who sells the pistons also offers the cylinder deck work for an extra $60.00.

[yellowbeard]

shouldn't mine aready been decked since it had a 76.44 mm piston in it?

[scrawny]

hey guys, 1upfront has it posted ^ that 72mm = 295cc. what I'm looking at is 76.44. So, if 72mm is 295cc what is 76.44? Joe

nope, 295 is with the 76.44 bore, the 72mm bore is 262cc's.:naughty:

[yellowbeard]

shouldn't mine aready been decked since it had a 76.44 mm piston in it?

[1upfront]

Your missing my point here man if it's truly a hondaline 300r cylinder it's a few mm's taller than the factory 250 jug aswell as 6mm larger bore but adding height to the jug requires a increased deck height in the piston to fill the gap. So if your cylinder measures 76mm or larger its a 300r kit but your options are limited with the hondaline bigbore pistons because they're discontinued and the ones I showed you are for the 3 or so mm shorter stock cylinder with the LA sleeve bigbore sleeve kit installed, that explains why you would have to shave a few mm's of the top of your cylinder if you where to use one in a true hondaline 300r cylinder.

[yellowbeard]

So what your saying is that the piston, that came out of the motor (76.44 mm) is a few mm's taller than the one that I will order. In other words the one that I have is the one that came stock with the big bore kit. I have a friend that has a machine shop. where can I find out how much it has to be decked for a 76.44 or 77mm depending on what I order. Sorry for the misunderstanding, did not realize this was stock piston for big bore kit. thought that since it had this piston in it, that it had already been bored and decked.

Just a question: would it not have the same compression with the piston a few mm's shorter, without decking it.
thanks for answering all these goofy question for me. But I've always heard the only dumb question is the one not asked. thanks Joe

[cr480r]

Just a question: would it not have the same compression with the piston a few mm's shorter, without decking it.
thanks for answering all these goofy question for me. But I've always heard the only dumb question is the one not asked. thanks Joe

Without reducing the deck height the compression would be virtually non-existant if the piston was 3mm shorter... That amount of material must be removed from the base of the cylinder or else drastic changes to the port timing will occur...

[yellowbeard]

ok, guys I see now that I have to get my cylinder decked, for a (76.44) or (77.50) does anyone know how much? Thinking about ordering a piston from L.A. Sleeve.

[1upfront]

Just have the guy that supplies the piston do the modification he offers the service on his ebay listing this is what it says.
* Fits hondaline ATC300 Air Cooled Big Bore Cylinder Kits.

* We Stock Replacement Pistons for the Honda ATC300 kit in the following sizes
* 76mm, 76.50mm, 77mm, 77.50mm. Stock bore is 76mm
* Forged Piston for Superior Strength & Resistance to Detonation.
* Cylinder Requires modification to convert from hondas piston to this style piston for the first time.
* Afterwards you can simply bore to the next over size piston
* Send in your Cylinder We do the modification, Bore, Hone for $65.00 labor With a 1-2 day turnaround

[Bryan Raffa]

sounds like a pretty solid deal right there..

[yellowbeard]

I think I will just send my cylinder to him, sounds like the thing to do. thanks guys.

[1upfront]

No problem man.