DT125R ARCHIVE

gasto · DTR Respected Member

3MB and 3BN cylinder differences

the only way is YAMAHA DTR · Guru

the first dt's had 3bn cylinders and which was nickasil plated then later dts had 3mb cylinders and 3mb head, then 2000 - 2003 ish had a 3bn head fitted with a restricted squish band, i swapped my 3bn for a 3mb head and had alot more bottem end power, 2004 onwards wasn't restricted

http://p1.bikepics.com/pics/2011/04/09/bikepics-2184568-full.jpg

llook at the chart

http://translate.google.com/translate?hl=en&ie=UTF-8&sl=auto&tl=en&u=http://www1.ocn.ne.jp/~ykt/4djb.html&prev=_t&rurl=translate.google.com

-- Edited by the only way is YAMAHA DTR on Saturday 30th of April 2011 08:46:47 PM

gooner78 · Guru

Is it just a straight swap between the heads thanks

the only way is YAMAHA DTR · Guru

yup hard to get hold off tho im lucky mine cost £20 and sold the 3bn for £30 lol

gasto · DTR Respected Member

i am planning to get my 3bn machined with different squish characteristics.I am also thinking of putting on one from yz 125.Any one tried that before?

gooner78 · Guru

how does the 3bn head restrict the engine thanks

-- Edited by gooner78 on Monday 2nd of May 2011 07:02:39 PM

gooner78 · Guru

http://cgi.ebay.co.uk/KTM-LC2-1999-Yamaha-DTR-125-1998-1999-Cylinder-Head-/150494378832?pt=UK_Motorcycle_Parts&hash=item230a29fb50#ht_1776wt_905

-- Edited by gooner78 on Monday 2nd of May 2011 07:11:23 PM

gasto · DTR Respected Member

the cylinder heads are designed different.The 3bn gives lower compression

NEV · Guru

RE: 3MB and 3BN cylinder differences

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the cylinder heads are designed different.The 3bn gives lower compression

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View image O.K Which is which then? View image

DT-R_bradders · Guru

gasto wrote:
the cylinder heads are designed different.The 3bn gives lower compression

i would of thought the compression is the same tbh, the squish band is there to "squish"all the feul/air around the tip of the sparkplug when the piston is at or near TDC to ensure all of it gets ignited all at once to prevent detonation/pinking , and to improve performance, the one in the pic on the left would reduce this because its not as smooth so some of the feul/air would get trapped around the outer ring therefore reduing performance as the effiiency of burning the gasses are reduced = less power

DT-R_bradders · Guru

have a read biggrin

http://etonracing1.homestead.com/Two-Stroke-Porting-Technology.html

Gambodia · DTR Senior Member

Iv got a 3mb head & barrel but my bottom end is a 3bn, is there such thing as a 3mb bottom end? What would the noticeable differences be between the 3bn &3mb bottom ends?

Calum122 · Guru

Type in 'dt engines' into search mate. And read it cover to cover. We discuss everything in there and come to a conclusion.

This thread is actually wrong.

Yes the 3BN comes from a earlier dt 1988 dtr NOT LC. Which suggest it migbt be an import. Since we know the dtr from 1989-2004 the the e 2004-2007.

The 3BN is NOT Nicosil plated! Its bore is 56.40mm and the standard is 56.00mm. Thus the stroke must be shorter in order to maintain cc's. if you do convert you'll want to use two base gaskets.

KenDOG has successfully done this conversion. Although the powervalve is different between the models despite being coded 3BN. Thus you must find the correct powervalve code unknown.

scrimsmustang · DTR Mechanic

Its 3BN-1131A-00-00, the later ones fit with a bit of modding.

scrimsmustang · DTR Mechanic

Oh and the stroke is not shorter, only the cylinder and head are coded 3BN, the actual model code for an 88 UK DT125R is 3DB1........

Check out megazip for all the model codes and part numbers, its in Russian but google translates it

www.megazip.ru/ru/bike/yamaha/view/435

scrimsmustang · DTR Mechanic

Its got all the TZR and TDR model codes and part numbers also