A forum for owners of Yamaha TTR250 trail and enduro bikes!

ttboof · Super Guru

Head gasket bugger

TTRfan · Super Guru

Bad luck Les cry

The only head gasket that blew on an engine I rebuilt was where the front LH head stud was binding in its threads so the torque wrench was clicking before the head was actually being tightened down - not had it before or since but I do check those outside stud crankcase threads are clean before the head goes on now wink

I hope you find a gasket!

Brian

ttboof · Super Guru

Thanks. I thought the same. Will give it all a good clean up and try again. I'm thinking the threads - can't remember lubing them when it went together

Got head and base gasket ordered Will arrive Wednesday only ones are in Sydney only four hours drive each way I was tempted but will be patient and get everything 110% and take my time

About to pull it down

ttboof · Super Guru

All looks good found I'd put two washers on one stud and none on one outside one so wouldn't have tightened down enough and the threads need a clean just in case

Now have to wait a few days for a new head and base gasket

Will be realy clean again

-- Edited by ttboof on Friday 8th of February 2019 02:00:44 AM

Kaos · Senior Member

Good you worked out why it went, bet you won't do that again. ;)

ttboof · Super Guru

Sure won't I'm missing a couple of days riding

Kaos · Senior Member

Looks a bit different without the cooling fins!

ttboof · Super Guru

Got a sample tile and some emery paper cleaned up well and checked the surfaces are flat

TTRfan · Super Guru

Did the outside studs thread in easily with no binding Les?

Brian

PS you always amaze me how quickly you get stuck in and get things sorted!! smile

ttboof · Super Guru

Ran a tread tap through the threads yes they were a bit tight

I'd say your spot on

I did try all bike shops in a 200k radius for a gasket if they had one it would be going by the morning biggrin

ttboof · Super Guru

Had a spare hour cleaned up the casting marks opened the exhaust port a bit then polished it with 400 then 800 grit paper will see if it makes a difference

Pic isn't very good cleaned out with brake cleaner and compressed air

TTRfan · Super Guru

I recollect being told that it's a "good thing" to check the joint between the carb stub and the head to make sure that the gas goes in smoothly and that there is no "step" to disrupt the flow. Not sure if I have explained that properly disbelief

The consensus also seems to be that you don't polish the surfaces of the inlet tract as, leaving them a bit rough, helps mix the petrol/air going in.

Brian

ttboof · Super Guru

Spot on Brian

The inlet on the ttr is good. The surface crates a bit of turbulence to mix fuel and air and is shaped well . The exhaust was OK will see if a bit of a tidy up helps . My first mod way back was cleaning the weld up in the header pipe as it was really rough and about one mill high all round made a bit of an improvement .not chasing a big improvement just a tidy up

leigh · Senior Member

Bugger, but TTR so it will be fine.

Whats your technique for removing the base gasket etc. Looks very clean (head side), I notice you mentioned emery paper.

Mine base gasket was stuck like cement to the barrel side and had to use a razor blade to scrape it off, took an hour or 2 - and despite taking my time and being super careful I was mortified at the result. The barrel mating surface was covered in nicks and scratches. At the time I didn't think you could use sealant on the gasket as well. Wish I did, it isn't leaking after 5000k or so but I'm not happy about it!

If there is a next time, I will need to do a better job. Wasn't sure if you could smooth it off a bit or I did it completely wrong, or just use sealant as well and forget about it.

Cheers Leigh.

ttboof · Super Guru

Head gasket surfaces emery paper on a flat surface

The bottom surfaces cleaned up easy with a blade may have been lucky but no evidence of sealant on the gasket Will be going back dry as the original never leaked. For the sake of $12 I'm putting another new base gasket on

-- Edited by ttboof on Tuesday 12th of February 2019 08:14:35 AM

leigh · Senior Member

Yeah might have been lucky there, was the original base gasket ok to get off?

Anyway mine was like it was super glued on the barrel side. Tried a few things to get it off and had to settle on a blade. Local Yamaha parts guy who knows his stuff said its common for them to leak at the base and they would often have them leaking from the base gasket on the showroom floor brand new.

Anyway, just paranoid about doing it again and stuffing the barrel mating surface.

Head gasket came off cleanly and both surfaces were perfect. Not so for the base gasket barrel side.

Cheers Leigh.

ttboof · Super Guru

Went to pick up new gaskets on the way home local bike shop found some so called you beaut non genuine gaskets for half the price

Made the call without asking me if prefer genuine but I have known the guys for 30 years so will see what there like tomorrow Arvo fingers crossed I want to be riding Saturday

Base gasket does stick to the cylinder a bit but a scraper wire brush and the secret weapon brake clean and patience

-- Edited by ttboof on Wednesday 13th of February 2019 07:29:29 AM

ttboof · Super Guru

About to reassemble apparently the bike shop uses this brand on rebuilds claim there pretty good. Will see

TTRfan · Super Guru

Steve sells those Cometic gaskets in the shop - great value. I have used them for years and absolutely no problems - except where I had the binding head bolt that is

You'll be fine Les!

ttboof · Super Guru

She's alive pic shows smoke off header

Thanks Brian and everyone for ideas and feed back I used a bit of sealant on the bottom gasket just in case

-- Edited by ttboof on Thursday 14th of February 2019 09:48:38 AM

leigh · Senior Member

Happy trails!

ttr steve · Super Guru

Well done, now get out riding smile

ttboof · Super Guru

Thanks Steve

I'm heading out first up in the morning

ttboof · Super Guru

Five hours in the forest and the bike is perfect I'm a bit stuffed .

Hope do do it again tomorrow.