Head



  • I want to get the most performence out of the TDR, so I have come across 3MB head. Now I have 4FU, the question is - Can I use 3MB head with 4FU barrel( saving up for a 3MB one)? My bike doesn't have domed piston, btw.



  • Yeah, you can use it, but it won't do you any favours.

    Since, as you say, the 4FU runs a flat top piston.

    My 4FU had a combustion ring in it, if yours does too then I'd have that ground out.



  • The ring is in the head or barrel? But if I get domed piston and later the 3mb barrel? The deal is just too good to let it slip by.



  • @killersbeez Meh, I'd stick with the nicasil plated 3MB 4FU for better heat disapation. The port timings look much better on the 4FU as well.

    https://www.youtube.com/watch?v=P8okvTxe-Bs&index=8&list=PL66C1264C7D6205BB

    The combustion ring on my 4FU is located in the head. It's really obvious. HOWEVER I was shown that not all 4FU's have this ring.



  • I didn't quite understand what You meant. I should stick to 4FU or go 3MB?



  • If it were me, I'd stick with the 4FU setup.



  • Well, I ordered 3MB head and domed piston. My barrel is messed up quite bad, it has 2 scratches from exhaust port to top like 2mm deep, and it is blowing my head gasket regulary. I would stick to 4FU barrel but it is quite hard to get hands on one :(.



  • @killersbeez Show us a pic of the bore mate. It might come out with a hone.

    The barrels aren't scrap mind you, they can be replated.

    The bores will take a battering before they're unusable, although the scores aren't good, it isn't always game over.



  • Well, at the moment I don't have any picture of it but it is similiar to this
    alt text
    Only my barrel has to 2 scratches and they are deeper. I came to conclusion that the previous owner decided to take it for a spin when he had rebuilt it, but "forgot" to put exhaust on and the tire threw some stone or something and it did few strokes with the rock in it. But i will probably pull the head this week to get a good photo of it.
    Also quick question so I don't have to make new thread- does DT 125 pipe fit TDR there is some buthering to it too( last owner decided to pull the stuff from silencer and welds are 45 degrees on the pipe where they should of been smooth)?



  • @killersbeez Yeah okay, that needs replating I'm afraid.

    The scores look too uniform to be debris. My guess, incorrect installation of the piston.

    Notice how it's on the "cool" transfer port, not the exhaust port.

    The engine is going to be exhausting gases outwards, and it's only the exhaust pipe that causes a forced induction of lost charge through the exhaust chamber.

    Therefore we can conclude that it's probably not fed in through the exhaust port.

    The barrel can be saved, it needs replating. Can be costly though with plating costing around £130.



  • You misunderstood me, this is just a picture for reference. On mine scratches are on the exhaust side. : )
    And what about the exaust pipe?



  • @killersbeez Sorry mate, I am busy doing something at the same time lol.

    Yeah, if it's worse than that then it needs a replate.

    I still think it's unlikely that something got into the exhaust port, but I guess it really doesn't matter too much. What matters is what are your plans.

    Again I don't know what benefits you will get, if any, of a 3MB over a 4FU. I think it's the complete package. If you got the barrel as well...

    The head must not have any pitting in it for it to be any good.



  • Well here is a photo of the head -alt text
    Yea, I know that You need the full package but i will get it eventually.



  • @killersbeez Yes mate. Clean head.

    What size is the piston on the 4FU?



  • It's standart bore, it is in pristine condition, not oval just the scores.



  • Try and get the 4FU fixed, they are Nicasil plated bores, so yes it's expensive to repair the cylinder wall regardless, but I believe the transfer porting is better than a 3MB.



  • @darty I reckon they are too bud.



  • @calum you mention head pitting what caused this and this leads to poor performance?



  • @declan Detonation can cause this, this happens when the fueling isn't set up properly, causing the fuel to ignite before the piston reaches TDC, in other words without the spark plug igniting. This causes masses of problems as the force of the piston going up is met with the force of the explosion. Destroys bearings and pits the head.

    A piston failure or debris will also cause pitting. But for tuners it's usually detonation.



  • Are the barrels really plated? Which models is that? Could have sworn than mine was steel lined.


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