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

Michael TTR250 · Veteran Member

Quick question ref. fitting new piston

TTRfan · Super Guru

RE: Quick question

TT-R250M · Super Guru

That is correct...

Jarrah

Michael TTR250 · Veteran Member

Thanks guys, and thanks for the ring gap picture Jarrah that would of most likely been my next question.

TT-R250M · Super Guru

Michael TTR250 wrote:
Thanks guys, and thanks for the ring gap picture Jarrah that would of most likely been my next question.

Yeah, I kinda figured that.

No problems, here to help.

Jarrah

TT-R250M · Super Guru

Here is some nice pictures of the cam marks and position of the cam lobes..

Position of the cam lobes..

Timing marks..

Enjoy!

Jarrah

Michael TTR250 · Veteran Member

Ok, so have compressed/closed the rings and piston has slid over up into barrel till rings can't be seen from underside, but won't go any further. should I be oiling the barrel or is there any other technique? The reborer had the new piston to bore to so I am assuming it is right???

TTRfan · Super Guru

It seems unlikely the rebore would be wrong. Did the piston without the rings pass through the barrel OK?

If so, it could be that a ring isn't seating properly.

I use a decent amount of oil when fitting pistons so that there is some lubrication on start up pending the oil circulating.

Brian

Michael TTR250 · Veteran Member

I didn't think to check the piston without the rings, I guess I could remove them and try it, have put some oil on and still no go?

Michael TTR250 · Veteran Member

Success, on close inspection the bottom compression ring had jumped out and was against the wavie one. it's tight but has gone on. As you suggest I will oil it up.

Thanks Brian.

Michael TTR250 · Veteran Member

Calling it a night and tackle again fresh in the morning. barrel and head gone on but now chain seems to have shrunk (I suspect it has caught up a bit on the bottom of the cog somehow as also I cant turn the wheel fully around to get it back to TDC, seems to be jammed) so will have a good night sleep and look at it tomorrow.

Any thoughts gratefully accepted.

TT-R250M · Super Guru

The chain is caught in the crankshaft drive gear. You will have to take the clutch cover off to free it if it does not free itself easily. This is why I leave the clutch cover off until last as a precautionary measure.

When you free it, use a piece of wire with a hook on it to pull the chain tight to prevent it from getting caught. When turning to TDC, hold it as tight as you can with one hand while turning the crankshaft with the other.

Jarrah

Michael TTR250 · Veteran Member

You da man, is the clutch cover the small one with the three allen head bolts?

Thanks mate,

TT-R250M · Super Guru

Michael TTR250 wrote:
You da man, is the clutch cover the small one with the three allen head bolts?

Thanks mate,

No, that is the oil filter cover. It would be an idea to clean it or replace if needed.

The clutch cover is on the right side of the engine.

Clutch cover on...

Clutch cover off...

This is a close-up of where the chain will be caught...

Jarrah

TT-R250M · Super Guru

While you are there, don't forget to clean the pre-oil filter screen..

Michael TTR250 · Veteran Member

Ok, thanks for the tip on the oil filter, I have a spare so I will do that. So I guess drain the oil then undo that cover, does it have a seal or gasket that needs to be replaced before going back on?

TT-R250M · Super Guru

Michael TTR250 wrote:
Ok, thanks for the tip on the oil filter, I have a spare so I will do that. So I guess drain the oil then undo that cover, does it have a seal or gasket that needs to be replaced before going back on?

When cleaning the oil filter be careful not to loose the O-rings...

Yes, drain the oil before taking the clutch cover off. The clutch cover has a gasket that can be used again if carefully taken apart. Sometimes it will stick to the mating surfaces and break though. Use a Stanley blade (CAREFULLY) to unstick the gasket and prevent it from breaking (if possible). You can always use a little oil resistant gasket goo at the breaks if you don't want to buy a new gasket.

Jarrah

Michael TTR250 · Veteran Member

Thanks again, so very much!

Michael TTR250 · Veteran Member

Sorry to keep bothering you Jarrah, so as shown I am at TDC however the cam lobes and the timong marks look slightly out (compared to how I took them of and your pictures) should I release the tensioner and move the cams one link or have I missed a step somewhere?

thanks

TT-R250M · Super Guru

Michael TTR250 wrote:
Sorry to keep bothering you Jarrah, so as shown I am at TDC however the cam lobes and the timong marks look slightly out (compared to how I took them of and your pictures) should I release the tensioner and move the cams one link or have I missed a step somewhere?

thanks

No problems Michael, ask as many questions as needed.

Unfortunately it looks like your cam chain is stretched. Did you replace it?

Do not move the timing, it is correct!

Jarrah

Michael TTR250 · Veteran Member

When took it apart a week ago I had a really good look at the lobes and timing markers, as they were lined up where they should be I thought ok that's good chain does not looked stretched so won't replace it. That' why I am surprised now that it won't line back up correctly?

TT-R250M · Super Guru

Michael TTR250 wrote:
When took it apart a week ago I had a really good look at the lobes and timing markers, as they were lined up where they should be I thought ok that's good chain does not looked stretched so won't replace it. That' why I am surprised now that it won't line back up correctly?

When you caught the chain you may have stretched it. It is very important to make sure it does not get stuck.

It may be a hassle to replace now but it will be even more of a hassle if it slips and damages the valves.

Jarrah

Michael TTR250 · Veteran Member

Sound advice, your right I must of stretched it. Does the head and barrel need to come off again to replace the chain or can it be feed through?

TT-R250M · Super Guru

Michael TTR250 wrote:
Sound advice, your right I must of stretched it. Does the head and barrel need to come off again to replace the chain or can it be feed through?

You will need to take the clutch basket off. To do this you will need a clutch holding tool such as the one pictured below to remove the clutch boss nut. In addition to this you will need a universal puller like the one pictured below.

To remove the clutch boss nut..

To remove the clutch boss...

More info here... http://ttr250.activeboard.com/t50977234/homemade-special-tools/

If you want to fit the cam chain without doing this, you can cut the old chain off (using a clean rag to make sure nothing drops into the engine) and buy one of these... http://www.ebay.com.au/itm/CAM-CHAIN-suits-YAMAHA-TTR250-1994-2010-/271305751279?pt=AU_Motorcycle_Parts_Accessories&hash=item3f2b153aef. You will need to peen the chain once fitted.

If you are prepared to pay the postage both ways I would be happy to lend you the tools required. It may be better to buy them or make them though?

Jarrah

Michael TTR250 · Veteran Member

Yeah going into the clutch is getting way over my head so I think that leaves two options, 1) give it to my local dealer who will charge me what 4-6 hours to do it??? or 2) try the cut chain option. I have a chain breaker (which I think has something on it to peen the chain), do you think the cut option is ok? does it come in the right length or do you cut it to suit?

Michael TTR250 · Veteran Member

Just had a look at the ebay add properly and the chain is the correct length.

TT-R250M · Super Guru

It is really not that hard with the correct tools, all you do is remove the clutch plates, remove the clutch boss nut, remove clutch boss, remove clutch basket, remove oil pump drive gear, fit cam chain.

I cannot see a problem with using the peened version, the chain will come in the correct length according to the add on eBay.

Jarrah

TTRfan · Super Guru

It is not unusual for the cam chain to jam on the bottom cog. Perhaps I have been lucky but I have always been able to free it by pulling hard upward on the cam chain whilst gently rocking the engine to and fro with a T bar on the flywheel bolt.

Brian

Michael TTR250 · Veteran Member

RE: Quick question ref. fitting new piston

TTRfan · Super Guru

Sorry - should have looked back over the thread before posting disbelief

Did you see Kenny's post here - http://ttr250.activeboard.com/t54842972/raid-revival/?page=1#lastPostAnchor - scroll up one message to see his pics of the cam chain timing marks at TDC. Yours are almost identical.

If your cam chain was worn then the cam gear lines wouldn't be parallel.

Just a thought....

Brian

Kenny R · Veteran Member

Yep, my flywheel timing mark is telling porkies.

My cam chain is tight between the cams and the tensioner is working ok and is around halfway along it's travel and the guide blades show no sign of wear.

Moving the cams one tooth is much to extreme a movement.

You would have to get a dial gauge or some other instrument to measure when the piston is at true TDC and check where your mark ends up.

Are you saying that they lined up before you started working on the bike but don't now?

Michael TTR250 · Veteran Member

That's what I thought however, I pulled the tensioner out again to make sure it was releasing properly (in the manual it said turn it till it stays in place which I did, while on Brians "step by step" it said hold the small screw driver in place while reinstalling which I did the second time) and after reinstalling it the second time I noticed the timing marks seemed now to only be only the tiniest fraction out (nowhere like it was before), I called the mate over who was helping me take the engine apart as he was sitting on that side of the bike and feels that's how it was when we dismantled it. So I put the bike back together, crossed my fingers and hit the starter. While I have not ridden it yet, no strange noises on start up or running in neutral for 5 minutes or so, I am hoping it may have been just a bit of play in the chain/tensioner or perhaps something as you say with the flywheel timing mark.

As I don't race or anything high tech I don't need 10/10 performance, but of course I don't want to crunch valves against the piston either.

Will let you know what happens after a ride this weekend............

TT-R250M · Super Guru

Glad you got it sorted!

At least you now know what is involved in replacing the cam chain. If you are concerned that it is still a little stretched, use a manual tensioner like the one in the link below. You can manual adjust the slack so it gives you more adjustment than the auto tensioner. http://www.ebay.com.au/itm/TIMING-CAM-CHAIN-TENSIONER-MANUAL-ADJUSTER-1999-2006-YAMAHA-TTR250-TTR-250-/160950999231?pt=Motorcycles_Parts_Accessories&hash=item25796d58bf

Of course it would be better just to replace the cam chain if it's too worn but this does offer a solution to a slightly stretched chain.

Jarrah

04TTR250 · Veteran Member

i always fit a new cam chain when i rebuild a bike, saves the hastles of doing it later.

TT-R250M · Super Guru

04TTR250 wrote:
i always fit a new cam chain when i rebuild a bike, saves the hastles of doing it later.

+1 wink