Hmm now what (A Rebore!)

Pablo13

I'll be keeping a close eye on things, regular compression tests and plug chops to see whats going on.

I think I've done what I wanted with the head for now. I'd say I've given it more of a polish than anything

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Its far far from perfect, but also a lot better than what it was :smiling_face_with_open_mouth:

one of the marks is still fingernail deep, but I'm reluctant to go much further without taking it somewhere knowledgeable with two stroke machining. I'm happy enough to fit and find out for now :winking_face:

NINJA

@Pablo13 It looks a lot better for-sure, let us know how it runs once you've finished your rebuild. :thumbs_up_light_skin_tone:

Calum

@Pablo13 That's a million times better, let's hope you haven't modified the squish.

With a bit of luck, the carbon build up ought to fill in the gaps lol

declan

@Calum heads really aren’t expensive I see them all the time for 30 pound but that said I’d be more than happy to run that head

Calum

@declan Cheap as chips mate.

https://www.ebay.co.uk/itm/Zylinderkopf-original-Yamaha-DT-125-R-RE-X-Motor-Head-Cylinder-3MB-11111-01/253954004870?hash=item3b20d69786:g:7TgAAOSwfONb1ce2:rk:9:pf:0

£140 he wants for that 3MB.

Used to be able to get them for £30, but not anymore. You can only get restrictive 3BN heads these days. Which need money spent on them to bring the power back up. Which he could just do to his current damaged head.

https://www.ebay.co.uk/itm/A-CYLINDER-HEAD-THERMOSTAT-MOTORRAD-YAMAHA-125-DTR-DT125R-DT-R-DT-R-3NC/264119708974?hash=item3d7ec2ed2e:g:qDAAAOSwuMZbm0qz:rk:21:pf:0

These look unrestrictive, but I don't know if they fit.

https://www.ebay.co.uk/itm/YAMAHA-DT125R-DT125-2T-MOTORBIKE-PART-3BN-ENGINE-CYLINDER-HEAD/113130967567?hash=item1a5721920f:g:sxsAAOSwWV9bPeMp:rk:23:pf:0

https://www.ebay.co.uk/itm/A-CYLINDER-HEAD-THERMOSTAT-COMPLETE-3BN-MOTORRAD-YAMAHA-125-DTR-DT125R-DT-R/264119710361?hash=item3d7ec2f299:g:mfoAAOSwNJxbm54o:rk:29:pf:0

https://www.ebay.co.uk/itm/A-CYLINDER-HEAD-MOTORRAD-YAMAHA-125-DTR-DT125R-DT-R-DT-R-4BL-TYPE-ENGINE-3NC/264122889180?hash=item3d7ef373dc:g:qRIAAOSwd49btxpP:rk:38:pf:0

If you find a 3MB for £30 in usable condition, buy it. Would be myt advice.

Pablo13

Its back together and running. Not ridden yet, but let it get to temp and adjusted idle. Took about twenty kicks to start first, but now its starting first kick. Took a compression reading before I started the engine with the exhaust off

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Pretty busy tomorrow, but If I get a moment Ill take it for a spin and see what is what

Calum

That's odd. Why did it take so long to start?

You made sure the oil pump does not have any air in it and is operating correctly?

Pablo13

@Calum I'd adjusted the throttle too much so when I fired it idled around 7k I think was the reason. Took it out for 15 gentle miles yesterday and all seemed well, and took to work this morning, so far so good. Just trying to be gentle and keep the revs relatively low for the meanwhile and get some miles under her belt.

Irongamer727

My big bore Athena made 14 bar compression.

NINJA

@Irongamer727 Man that's insane, it ran fine like that???

Pablo13

Little update. After running it in a little and opening it up a bit, I wasn't particularly impressed. It felt worse than before up top. So I did mess with the squish too much I think. Luckily managed to get another 3mb head in a more normal condition for £25 and have just fitted it and compression tested it and its up, so hopefully tomorrow's ride will be an improvement.

Now I have the old head here may as well look into getting it sorted properly at some stage and swapping back later down the line.

Calum

@Pablo13 £25 is very reasonable. Not damaged in any way?

NINJA

@Pablo13 Yeah nice one, post some pics of the new head if you have any bud???

Pablo13

@Calum It had a few small nicks, but was a whole load better looking than the other. Got it from where I bought the bike, it was the best 3mb he had, got loads of the more restrictive ones though.

Sadly no snaps NINJA, I think maybe it's a slightly older head as it had 3mb and Yamaha embossed on the top of it which the other does not

NINJA

@Pablo13 COOL so long as it works fine, then your good_to_go!!!!!!!!!! :grinning_face_with_smiling_eyes:

Calum

@Pablo13 If the other one did not have 3MB stamped on the head then it wasn't a 3MB head. Yamaha used the 3MB all the way till they discontinued the engine. I had a few non-stamped heads and run run on my dt.

The majority of power is made or lost in the head, so it is important to get it right, but I am surpised you noticed it. I would have felt you would have needed a dyno...make sure the bike is setup right. I fear something else may be amiss and might be a little expensive

Irongamer727

@NINJA yeah I got a bad exhaust so it's not making that much power really. It's got a whole lot of torque and I get very good gas mileage.

Pablo13

It's still basically the same

Gotta be something else....not much left really, CDI, crankcase seals or clutching at straws for an extremely worn carb?

I've never inspected the reeds and the exhaust is a bit of an unknown, so could both be causing possible issues and shouldn't be overlooked.

Got a second hand CDI winging its way to me to rule that out. I'll do that and go from there....

NINJA

@Pablo13 I would start simple, have you checked the plug or did you fit a new one? Perform a plug chop to see what the condition of the plug is, which will give you some clues as to what is happening.