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Discussion Starter · #1 ·
Hi guys,im looking for some help on the difference between a 3MB and a 4FU prefix barrel.I understand the 3MB was fitted to the DTR and the 4FU fitted to the TZR 4DL Model, is it correct that the difference is only in the porting?
Main reason for asking is ive just bought a TZR 4DL and it has a 3MB barrel fitted, my fault should of checked before I did the deal. although I don't think all is lost.any advice would be great thanks.
 

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If I remember correctly FU is the plated series 2 4dl barrel, uses a slightly different head, different head gasket, piston crowns flat, & a different spark plug, the ports are almost identical but the 3MB inlet port is bigger & the exhaust ports are slightly different. I have a 3MB00 on my 4dl1
edit: & with the 3MB00 the piston should have a 10mm hole on the inlet side, for lubing the small end bearing
 

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Discussion Starter · #3 ·
If I remember correctly FU is the plated series 2 4dl barrel, uses a slightly different head, different head gasket, piston crowns flat, & a different spark plug, the ports are almost identical but the 3MB inlet port is bigger & the exhaust ports are slightly different. I have a 3MB00 on my 4dl1
edit: & with the 3MB00 the piston should have a 10mm hole on the inlet side, for lubing the small end bearing
Thanks for the information,the lad I bought it off says its just had a bore and piston, but now its making a ticking noise, it does sound like the little end,but im guessing its either the PV or the head gasket just being touched by the piston, Im going to pull it down and see whats going on.
 

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Think you should be safe with the gasket mines +1.4mm OS & havn't had a problem but the pv did need some flatting back just around that 50odd degrees where it reaches in. When mine was touching i could feel it catching the piston when manually turning the pv & add a tiny gap for the pv expanding when hot. Did he fit a new small end bearing during the rebore?
 

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Just for clarification, as I know barrels seem to be confusing,
4dl series one and three use the 3mb barrel,
4dl series 2 uses the very rare 4dl-00 barrel a it's an sp
The 4hw/4fl use the 4fu plated barrel, as do some DTR's
And some DTR's use the 3mb barrel too.
The porting is slightly different between the 4fu and he 3mb and the 4fu is Nicosil plated an uses a higher compression head, but the 4fu has less aggressive porting.

So if your bike is the 4dl then it has the right barrel on it :)
 

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Just my 2 penneth, The DTR125R only used the 3MB00 barrel and never nicosil plated. TZR5000 really knows his TZR125R stuff and I am sure he just unintentionally didn't explain quite right that the 4DL markings on the barrel have 3MB00 P 124cc, the "P" being stamped on later. If it doesn't have the "P" stamp then it is just a DTR125R barrel, also some highly port restricted DT125R's have a 3BN00 barrel and head, I don't know what country they were intended for but if anyone wants to restrict their DT to a 3BN barrel and head they are quite welcome to the set I have !!! Yes I know but why?. TDR125's I have never had dealings with so I will keep quiet on that one.
 

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Discussion Starter · #7 ·
Just my 2 penneth, The DTR125R only used the 3MB00 barrel and never nicosil plated. TZR5000 really knows his TZR125R stuff and I am sure he just unintentionally didn't explain quite right that the 4DL markings on the barrel have 3MB00 P 124cc, the "P" being stamped on later. If it doesn't have the "P" stamp then it is just a DTR125R barrel, also some highly port restricted DT125R's have a 3BN00 barrel and head, I don't know what country they were intended for but if anyone wants to restrict their DT to a 3BN barrel and head they are quite welcome to the set I have !!! Yes I know but why?. TDR125's I have never had dealings with so I will keep quiet on that one.
Hi,thanks for all the excellent information..just checked and mine has the 3MB P 124cc...barrel, so all agreed it has the right barrel. ok well I stripped the top end off and some monkey has bored it and fitted a 56.4mm standard 2RK piston..oops..its a cheap nasty piston and is in a bad way ,looks like its been nipping up. my thoughts are do I buy a DTR125 R +.50mm piston and just have my barrel cleaned up,to take it to (56.50mm), as its not picked up...can a DTR 1255R piston be fitted to my bike/ im aware that the std 4Dl piston should have the 10mm hole on the inlet side.any advice would be great. thanks again
 

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He must've use the same tool who did my rebore from 57 to 57.4. I only asked for +0.25 but he assumed it was a 56.4 standard despite saying exactly what bike it was..
I struggled to find a piston with a hole I ended up just drilling & chamfering it myself matching a standard piston.
It will run fine without the hole, just the small end bearing won't be quite as lubed as it could be.
 

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Discussion Starter · #9 ·
He must've use the same tool who did my rebore from 57 to 57.4. I only asked for +0.25 but he assumed it was a 56.4 standard despite saying exactly what bike it was..
I struggled to find a piston with a hole I ended up just drilling & chamfering it myself matching a standard piston.
It will run fine without the hole, just the small end bearing won't be quite as lubed as it could be.
thanks,I know some so called engineers just don't know their stuff. Im going to get a DTR125 R piston @ + .50mm and just get my barrel cleaned up, I will also get the hole put into the inlet side at the same time..thanks
 

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Glad you are getting sorted, regards getting the "proper" parts may I suggest PJME? I have just parcelled up a "p" barrel to be honed or rebored, I will let Paul decide and getting the piston/gaskets etc from there also. Only good references about them on here. Paul pops up on this forum now again. I think I am allowed to link http://www.pjme.co.uk/
 

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Sorry for the random question, but could anybody tell me what piston is meant for a 4fu barrel? I have recently converted to a 4fu on my dt125r but the piston part code is reading 1kt250, this code is for a 56.4mm tzr piston, but when holding it next to a 56.4mm it's noticeably bigger and wider?
 
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