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

leigh · Senior Member

Leaking base gasket - should I be excited or disappointed??

TTRfan · Super Guru

Hi Leigh and thank you for your kind comments about the tutorials - it's good to have such positive feedback biggrin

First off, you can only access the external head bolts easily. The internal bolts will require removal of the cam gear to get access so my suggestion is not to worry and go straight to the strip down.

Over the years I have come across a number of TTR engines that have "hydraulicked" following a drowning and they all seem to run OK for a while but further down the line they suffer from oil burning and leaky bottom barrel gaskets.

I am not a trained mechanic but the conclusions I draw from this is that the piston rings and/or their lands get damaged when the engine slams up against an uncompressible body of water in the combustion chamber.

Also, and again it is supposition, I think the force of impact when the piston stops dead against the water means something else has to give and that the head bolts get stretched slightly. Not in an obvious way but enough to allow the bottom gasket to leak after a while.

Anyone else think those are reasonable assumptions?

I think you have to wait until you have the barrel off before making a final decision but I am suspicious that just fitting new rings will not be a long-term fix cry

We are here to help. Let us know what you find.....

Brian

leigh · Senior Member

Hey Brian

Thanks for the advice, really appreciate it. I'll certainly let you know what I find and take photos ( and err no doubt have lots of questions)

When you say just rings might not be a long term fix, are you meaning replace piston as well and maybe new head bolts?

I hope you don't mean bottom end might be dodgy😢

My plan is to replace piston +2mm and rings, new gaskets , valve seals and I guess disasamble the head and clean everything, maybe new head bolts? Probably port and polish the head too while I'm at it.

Leigh.

ttboof · Super Guru

Doing the lot is an overhaul and ride again .just rings you may need to revisit and do the rebore ext some time soon

Brian's theory on water lock up I recon is correct everything is torqued down providing a small amount of stretch with the big hit there may be a bit of give in the bolts threads in the cases ext allowing the slight leak to develop .once re done should be OK

leigh · Senior Member

Makes sense. For the sake of a few hundred dollars I'll do the lot. Probably won't have to touch it for years.......if I stay out of trouble 😜

TTRfan · Super Guru

If you are following the guide here http://www.ttr250.com/Removing_Cylinder_Head/TTR_head_removal.htm Leigh then can you please feedback any bits you find confusing or anything missing please?

It is worth mentioning that moisture can sometimes get down the threads of the front left "outside" head bolt so make sure that the bolt and case threads are nice and clean before putting it back.

I doubt that your head bolts will have been damaged but Steve stocks s/h ones if needed - see https://totallyttrs.com/epages/699105d9-e4cc-4b32-b236-84e72cd67f84.sf/en_GB/?ObjectPath=/Shops/699105d9-e4cc-4b32-b236-84e72cd67f84/Products/TTR-0481

Brian

leigh · Senior Member

I will definitely be using those guides, I have a couple of basic questions so far but I will wait closer to the time and once I have done more research reading the manual etc so I don't pester you too much! Happy to let you know what I understood and what might be missing for a first timer like myself :)

I am guessing there is a different head gasket to go with the 2mm oversize piston and rebore? Does the head have to be modified by 2mm as well?

I will save a few $$ and then buy parts and get into it. I'll add to this then.

Cheers Leigh

.

-- Edited by leigh on Tuesday 13th of June 2017 12:09:21 AM

-- Edited by leigh on Tuesday 13th of June 2017 01:02:14 AM

TTRfan · Super Guru

Same head gasket fits all up to the max 2mm oversize.

No need to modify the head in any way. Just clean up the valves, fit new valve stem oil seals and lap the valves in.

Brian

leigh · Senior Member

Great. Roger that.

leigh · Senior Member

Further to this post - of course things go this way....

My leak had pretty much stopped and I've been getting ready for a 5 day trip with a mate doing around 1200klm - last night i noticed the gasket has let go and there is plenty of oil coming out. I'll add an engine strip to my to do list now! Leave in 2 weeks, just ordered the gaskets from Mr Yamaha as I don't think they would arrive in time from Steve. cry

Plan was obviously oversize piston etc but I don't have time for that now. It will be a pull apart, new gaskets and back together again. Am I silly to not add a new set of standard rings? Bikes done 25,000klm.

Cheers Leigh.

Edit: I have a torque wrench - is it essential to get the Motionpro tool to get some of the nuts/bolts done up? Is it possible to get the job done without? It is on my BUY list but not sure I can get one in time either.

TTRfan · Super Guru

Whether to fit new rings depends on what you find when you get the barrel off Leigh.

If you are pretty confident that your piston is standard then it would be worth having a new set of rings standing by in case they are needed.

If the bore and piston look OK then check the new top ring in the bore against the old one to check how worn the old rings are. If no difference then you could save yourself some money and not fit the new rings although, personally, having got this far I would fit them anyway!

You can do without the MotionPro wrench and use your judgement on how tight to go wink

Brian

katana · Senior Member

Replace the rings. It will make the bore and the piston last longer. Might as well do valve stem seals too. For how deep you are going, it is not overkill.

leigh · Senior Member

Thanks for the replys.

Your thoughts echo my own, in the end I ordered a set of standard rings with the gaskets.

Looking forward to seeing what it all looks like.

I'll keep you posted.

leigh · Senior Member

Doesn't look too bad. Bit of play in the conrod though, .8mm is the max I have a feeling it's more than that. Not sure how to accurately measure it.

Bore and piston appear to be in spec using my micrometer. I'll throw the new rings on

Cam chain is a little worn new one on the way

She'll be right because "race bike"

Had a oh crap moment when fiddling with the piston and the timing moved a whisker moved it back by pulling up on the crank/piston.

Cleaning gasket surfaces and assembly tomorrow

-- Edited by leigh on Saturday 11th of November 2017 08:03:44 AM

TTRfan · Super Guru

It all looks good in there Leigh biggrin

I can see where the base gasket was damaged. Is that where it was leaking - front right?

Both timing lines on your camshafts are almost exactly parallel to the head casting indicating your timing chain is not worn - what makes you think it is?

Brian

leigh · Senior Member

Yes that's its, leaking at the front right.

I thought because they didn't line up perfectly it indicated the chain was worn, I know its not too bad compared to other pics I've seen. New cam chain will go on next time I have to open the engine up.

It's almost back together, I stopped after checking the valve shims and confused myself.

Intake side has a 195 and a 192, exhaust side a 180 and 175. My 0.10 feeler gauge wont fit under either side, so they are all way out (gap to small). I haven't changed anything from it running so it was running fine but the clearances seem to be quite a bit out of spec. Just need to get shims now, are the ones for the TTR common?

I am confused because I'm either doing it wrong or they have a lot of tolerance either way, the min spec for an exhaust valve is 0.19mm and my .10mm feeler wont go under there so how does it still run? Seemingly perfectly. Out of interest what does it effect when they are not set correctly? Premature valve wear? Inefficient engine operation?

looking at the chart in the manual I need at least a 160 for the exhaust side maybe smaller.

Edit: I forgot to say the parts guy at my Yamaha dealer is an encyclopedia on Yamaha stuff and told me the base gaskets leaking is quite common on the ttrs. He said they have had them in there new for sale on the shop floor leaking from a base gasket.

Cheers Leigh.

-- Edited by leigh on Sunday 12th of November 2017 11:01:38 PM

leigh · Senior Member

All back together and running fine - apart from noisy tappets.

I didn't think I was that bad with a feeler gauge! Put the new shims in and they measured as being a bit too wide a gap, and I thought the shims might take me mid range in spec or not quite enough. Anyway I'll pull them out and put the originals back in and have a think about it and take it for a spin.

TTRfan · Super Guru

Well done Leigh - job done!

The exhaust valves can be noisy if adjusted on the higher side of the specified clearance so I tend to adjust those to nearer the bottom of the range.

Brian

leigh · Senior Member

Hi Brian, I think that was the case, I adjusted them on the wider side of the spec. I put the original shims back in and its now quiet as a mouse. I'll do them again soon, now I have a better understanding I'll probably get it right!

Thanks so much for all your help and the guide. I made a few errors and wasted time but overall it was a very satisfying thing to do. I took it for a spin last night and I'm surprised how much difference a new set of rings has made. Really glad I did that too.

I got the timing all sorted etc and put the cam tensioner in then realised the starter wouldn't fit back, DOH! pull it all apart again. Had things like that a few times. Lost TDC a few times so the first time that was a stress while i thought about how to get it back. Maybe you could add those to the guide?

Thanks again, I'd buy you a beer but we are a bit far away!

Leigh.

TTRfan · Super Guru

leigh wrote:
I got the timing all sorted etc and put the cam tensioner in then realised the starter wouldn't fit back, DOH! pull it all apart again. Had things like that a few times. Lost TDC a few times so the first time that was a stress while i thought about how to get it back. Maybe you could add those to the guide?

Thanks again, I'd buy you a beer but we are a bit far away!

Leigh.

I did just that the other day but it is possible to remove/replace the starter motor with the cam chain tensioner in place if you remove the 10mm bolt that holds the clutch cable retainer and move it out the way. See http://www.ttr250.com/Starter_information/TTR250_starter_motor_information.htm

I am always pleased to receive feedback and suggestions on how to improve the guides but if you followed this guide http://www.ttr250.com/Removing_Cylinder_Head/TTR_head_removal.htm it does say to put the starter motor in before the cam chain tensioner?

With regard to keeping the engine at TDC when refitting the camshafts and cam chain, it is difficult and I confess to getting Mrs TTR to help if she is around wink Otherwise it's a case of going back and forth from side to side to check.....

You never know, I might get close enough for you to buy me that beer one day biggrin

Brian

leigh · Senior Member

Haha, my wife helped with the same, can you please hold this cam chain and let it move through your hand while I do some cursing!

Well obviously I need to read things more closely, I did consider undoing the clutch cable, anyway all a good experience.

If you ever do make it out this way, a beer and ride is available anytime Brian.

Leigh.

JOHNYBOY · Super Guru

AS REGARDS TO A BEER I WOULD BUY YOU MORE THAN ONE BEER BRIAN BOOK ON WITH TTR STEVE FOR IOM NEXT YEAR WE WILL MEET UP SORRY FOR CAPS LOCK I JUST NOTICED JOHN

ttr steve · Super Guru

May be something we could do smile