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Post Info TOPIC: Piston Sizes For Different Barrels


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Piston Sizes For Different Barrels
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This is actually starting to do my nut in.

 

Can anyone help with this please?

 

Basically there is lots of contradicting informaiton out there on the net with Standard Piston Sizes for different codes of barrels.

 

For Example directly from the Haynes manual:

 

Cylinder barrel

Standard bore ID:

     TZR and early DT models (3DB1)....................... 56.40-56.42 mm

     Later DT models (3RN1 Onward)....................... 56.00-56.02 mm

 

Piston

Standard OD:

    TZR and early DT models (3DB1)......................... 56.34 -56.40 mm

    Later DT models (3RN1 onward)......................... 55.950 - 55.955 mm

 

Ok so that above is directly out of the Haynes.

 

So what is with the different internal Diameters of the earlier models. What was the code on these barrels. I'm mainly concerned with the DT side of things.

 

 

So from what I have read is that the 3BN cylinders have a 56.40mm Internal diameter. And that the 3MB cylinder is 56.00mm ID.

 

 

I've recently acquired a 4FU cylinder and will be looking into fitting it onto the DT bottom end. Can't find much information on the net about it's specs. Only that the bike was coded 4GW and that the cylinder is off a 1993 TDR. But what does that mean?

 

What I want to know is what is the standard piston size for the 4FU. i've measure it using verniers and all I get is the 56.00mm ball park. But how accurate am I measuring?

 

When looking for pistons on the net Woesnner reckon that the standard bore sizes are the same for my 1993 TDR and the DTRE

 

Standard4FUSize_zps47522584.jpg

 

 

Any help is appreciated. At least here it will remain for future people to refer to...

 

 



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Not sure of the piston size Calum, but the standard piston part number for a 93 TDR 4GW1 with a 4FU Barrel is 4FU-11631-00-a0.
The different size bores and strokes apply to pre 1989 DTR's, yours being a later RE 3BN bike will be the normal standard bore/stroke.

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Wow really? So DT's made prior to 1989 would have had that 3BN cylinder on it? Which was a bigger bore?

So in which case the 4FU should be standard bore size since it's made in 1993. Which should mean 56.00mm bore. The DTR wasn't important by companies before 1989 was it? As we were looking at that list you posted up. It didn't make the UK until 1989 and prior to that we only got the LC.

Cheers mate.

Saves me head scratching.

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mine was an E-reg 1988 DT125r infact E838 ALG if i remember correctly lol


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dread123 wrote:

mine was an E-reg 1988 DT125r infact E838 ALG if i remember correctly lol


 What was the code on the side of the barrel?



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i've got an e reg dt 125r at the moment,waiting for a rebuild. 

the 4fu's use the 56mm piston cal,lovely snug fit biggrin



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Cheers mate.

Thats my main question.

Although they don't make a 56mm piston. I take it it will be the 55.94mm piston.

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Doesn't the bore need to be 56.00, I'm sure there's meant to be 0.06mm clearance.

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David what did you run the 4FU on? Was it a tdr. I'm concerned about altering the port timings if i install this cylinder? I haven't got a 3mb to hand to work out if there is any difference.

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If i raise the exhaust port then i'll lose compression. So i'md need to skim the head or the top of the cylinder to gain this compression back.

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its running on a 3mb bottom end at the moment.

the port timing seems the same but its not been running for very long.

when i said the 56mm piston,i meant the piston for the 56mm bore omfg.gif



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Ok. Got it. Thats alright then.

So to confirm then dave. You put the 4fu briefly onto the dt.

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yes,its done about 3 heat cycles and half hour's gentle ride,

no issues so far....



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Nice one mate. Notice any power gains?

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not cracked it open yet,but it feels like its going to go well.

feels run in already confuse just read through skint's project as i remembered

he had a 4fu barrel and it is a 56mm piston LINK i'm sure i used a standard 3mb piston in the end



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Cheers mate.

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