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Barrel or Head cracked?

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darkangel
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Joined: 18 Aug 2007
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PostPosted: 13:36 - 25 Jun 2008    Post subject: Barrel or Head cracked? Reply with quote

Had my dt125r at the mechanics lately having a full engine rebuild. this was originally to fix a coolant leak issue which was from a blown head gasket, but the bike needed a rebuild anyway.
The bike was done and i ran it for 100 miles under 5k rpm, all was good. but now after i started using more of the rpm range 6k then 7k there is coolant being pressurized and ejected again!
The mechanic cleaned the barrel and head surfaces, they were spotless (he used wet and dry paper, is this bad?), he also said that they were not warped, we tried a replacement rad cap and still coolant is being lost!
Tomorrow he is taking the head and barrel to be checked by a specialist for cracks.
Anyone have any ideas? i cant really afford to be replacing a barrel or head.
The bike has had a blowout once where it overheated and dumped the coolant, i believe i stopped it before it hit the red though.
Any opinions would be appreciated!
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darkangel
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PostPosted: 14:05 - 25 Jun 2008    Post subject: Reply with quote

If it were cracked where would the crack likely be? would having a skim sort it?
The mechanic did a pressure check on the engine surely that would have picked up on this
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NSR Mick
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PostPosted: 14:10 - 25 Jun 2008    Post subject: Reply with quote

If it's cracked the cost involved in putting it right is likely to be more than the cost of replacement parts once you put the cost of getting them tested on top.

You could probably buy an engine for less than what testing and repairing is going to cost you.

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darkangel
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PostPosted: 14:18 - 25 Jun 2008    Post subject: Reply with quote

This is terrible.
I just had a full engine rebuild, and a new piston kit.
If thats the only option im going to have to sell my bike, contract with my job just expired, i need my bike for transport and im allready in debt for having the rebuild done argghhhhh

The mechanic mentioned nothing about the cost of testing, im going to have to ask tomorrow.

Would it not have been the mechanics job to identify this when he had the engine apart and then pressure checked it afterwards?
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NSR Mick
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PostPosted: 14:19 - 25 Jun 2008    Post subject: Reply with quote

Was it ok before the rebuild?
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sickpup
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Joined: 21 Apr 2004
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PostPosted: 14:23 - 25 Jun 2008    Post subject: Reply with quote

Yes it could be a warped head or barrel.

The pattern gasket kit for these is generic for most year but the base gasket is different on the later years models and needs an extra hole cut in it for a coolant channel or the bike over heats. Lots of mechanics miss that one.
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darkangel
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PostPosted: 14:25 - 25 Jun 2008    Post subject: Reply with quote

very good point! i did a top end on mine and never cut that out, and when i stripped it you could tell it needed to be removed as it was soaked and stained
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darkangel
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PostPosted: 14:43 - 25 Jun 2008    Post subject: Reply with quote

before the rebuild it had a blown head gasket
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darkangel
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PostPosted: 14:44 - 25 Jun 2008    Post subject: Reply with quote

Surely a leak down test would have shown a leaking head gasket, a warped head/barrel or a cracked head/barrel?
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cestrian
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PostPosted: 15:06 - 25 Jun 2008    Post subject: Reply with quote

About the wet or dry, I'm not sure I'd use wet or dry on a barrel or head, prefer to use engineers scrapers instead.
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darkangel
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PostPosted: 16:23 - 25 Jun 2008    Post subject: Reply with quote

anyone else?
I have never ragged the bike from cold i always warm it up properly, this seemed to happen after an overheat, would the overheat be more likely to warp or crack the barrel/head?
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Pete.
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PostPosted: 18:07 - 25 Jun 2008    Post subject: Reply with quote

If it's pressurising after a rebuild where it didn't before I would suspect what Sickpup says to be true. Ask the mechanic to check the base gasket.

The proper way to flatten the head/barrell is to lap it on a surface plate/lapping table. You can also use some fine grit wet & dry taped to a pane of glass ( I've used a double-glazing panel). Just rubbing it with wet & dry to clean it would be ok if you only used it to clean gasket residue.
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sickpup
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PostPosted: 18:14 - 25 Jun 2008    Post subject: Reply with quote

darkangel wrote:


Surely a leak down test would have shown a leaking head gasket, a warped head/barrel or a cracked head/barrel?



Can't really do a leak down test on a 2smoke. A leak down test is used to pinpoint an air leak from rings or valves on a four stroke.

A cracked/warped head or barrel will often only show up when a barrel or head heats up, the crack opens up as the metal expands.

In the past I've used a sheet of glass with grinding paste to lap a head.
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Aikman666
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PostPosted: 18:46 - 25 Jun 2008    Post subject: Reply with quote

Is there a temp guage on the thing to make sure that it isnt just plain overheating? Confused
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Pete.
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PostPosted: 18:51 - 25 Jun 2008    Post subject: Reply with quote

sickpup wrote:

In the past I've used a sheet of glass with grinding paste to lap a head.


I missed a 24-inch surface plate on eBay last week - went for under £30. Bloody forgot about the auction until it was to late Sad
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132.9mph off and walked away. Gear is good, gear is good, gear is very very good Very Happy
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sickpup
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PostPosted: 19:17 - 25 Jun 2008    Post subject: Reply with quote

Geri wrote:


I missed a 24-inch surface plate on eBay last week - went for under £30. Bloody forgot about the auction until it was to late Sad



Things like that hurt. Sad
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darkangel
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PostPosted: 20:23 - 25 Jun 2008    Post subject: Reply with quote

im sure its not just overheating, even at low temps coolant is lost
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megastreak140
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Joined: 22 Jun 2008
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PostPosted: 20:11 - 26 Jun 2008    Post subject: dt125 Reply with quote

had this problem on my 1990 dt125r used a cheap gasket kit of ebay was blowing water out of the rad got proper gaskets from yamaha stoped straight away just a theory could be usin cheap parts your michanic
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sickpup
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Joined: 21 Apr 2004
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PostPosted: 22:19 - 26 Jun 2008    Post subject: Re: dt125 Reply with quote

megastreak140 wrote:


had this problem on my 1990 dt125r used a cheap gasket kit of ebay was blowing water out of the rad got proper gaskets from yamaha stoped straight away just a theory could be usin cheap parts your michanic



Did you notice the base gasket modification needed? Wink
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darkangel
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PostPosted: 21:34 - 28 Jun 2008    Post subject: Reply with quote

It ended up that the mechanic had used a cheap head gasket and that had blown.
Stuck a yamaha one in and alls fine now! thanks everyone for your help, really appreciate it!
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2006 _p1
Crazy Courier



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PostPosted: 21:37 - 28 Jun 2008    Post subject: Reply with quote

Wet and dry wont effect it at all.
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