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The TTR250 FAQ web pages -> TTR250 -> Repairs and maintenance -> Where exhaust camshaft sits, worn. Could I have issues?
Post Info TOPIC: Where exhaust camshaft sits, worn. Could I have issues?
Lichi


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Where exhaust camshaft sits, worn. Could I have issues?
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Hi guys,

Some time has passed since I started working on this motorbike, and finally parts I have ordered arrived.

Today while trying to fit camshaft caps with new bolts, I have found that threads of some of them where stripped..so I have decided to take head apart to fix this.

Once I took head apart, I have seen something that haven't seen before - probably because was covered by camshaft, and I supposed everything was ok-.

I have found where exhaust camshaft sits, is worn. 

Original reason I have ordered new bolts for caps, is that when I first took the head/cam cover out, I found that all bolts where different, so I have guessed they have lost them ( remember Im in Thailand) and have replaced them with just ones they have found around.

Now Im realizing why so many different bolts (many threads stripped) and also wondering that maybe they have runned this bike with caps being loose and camshaft rubbed the walls where it sits.

Im attaching a pic to be more clear on explanation.

And asking, do you think after fitting caps correctly, as camshaft have already worn sits, would I have any issue?

Is there any way to measure this -i know how to check camshafts, but never thought about sits20170312_141541.jpg

20170312_141602.jpg-20170312_141707.jpg

Thanks in advance for cooperation.

Cheers,

Lisandro



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TTRfan


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Hi Lisandro

Don't panic! What you have found is quite common in that it the aluminium journals in the head score very easily.

The good thing is that they don't look blackened which happens when the engine is run with little or no oil.

My suggestion is that you clean the bearing journals on the camshafts to get them as smooth and clean as possible and then make up a simple tool as shown here http://ttr250.activeboard.com/t53051443/camshafts-too-tight/  and clean up the bearing surfaces in the head.

I am guessing that you will Helicoil (or similar) the stripped threads and fit the correct 6mm bolts.

The rub mark on the end casting of the head where the exhaust camshaft fits is odd and I am wondering how it might have been caused. Are there corresponding rub marks or damage on the sprocket or chain? The large exhaust camshaft cap should retain the camshaft in its correct position and not allow it to make such contact confuse

Brian



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Lichi


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Thank you Brian for information given.

Yes, plans are putting inserts for later fitting the bolts in actual stripped threads.

Also I have seen the chemical thread filler sold by Loctite, that seems to be just epoxy glue with some extra glue ( i don't know what is it yet) to paint bolts and avoid them sticking to new thread, once made by same bolt. Need to search more about this.

About rub mark where exhaust camshaft fits, as I said before, my guess was that camshaft caps were loose, and looks as the sprocket was the culprit to mark the aluminum journal( regarding how it rub looks) Haven't checked wear on the sprocket in detail, I will tomorrow.

My initial concerns were as aluminum journal head on exhaust looks deeper than intake ( first pic to see both), this could affect balance and make chain vibrate ( just my guessing).


Lisandro

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TTRfan


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The scoring looks more to do with a bit of swarf coming in with the oil and getting trapped at that spot. A loose cam cap would show different wear or damage marks rather than circular scoring.

When you have cleaned up the camshaft and journals, torque up the cam cap bolts and check if there is any up and down play on the cams. Hopefully there won't be and it'll be good to run.

Brian



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Lichi


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Hi Brian,

Thank you so much for advises.

I have checked today, and apparently what has rubbed the aluminum was the chain. Sprocket looks fine and chain has not much wear, so would be ok.

Unfortunately I will need to heli coil 5 threads that are stripped.... :(

As I need to order them and take minimum ten days to arrive, I don't want to miss the size. Do you think M6*1.25  would be ok?

Actually thread lenght is 1.3 but I cannot find inserts of this size. Or would be better 1.5 and drilling deeper?

Never did this job. In my country you call a guy that comes to your place and make it for you ( lazy guys) :)

Can you help me to double check this info please?

Cheers,

Lisandro

 



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One1


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Theres no way the chain did that. It doesn't run under the timing gear. The scoring is consistent with the circle of the gear, not the chain. The scoring is from the bolt in your gear being too far in. Either it is missing the washer or has been replaced with an incorrect length one. This is why your cam journals are eaten at that spot as well. Once the incorrect bolt was installed it grinded the case and the metal rotating upwards got sucked into your camshafts. 

someone repaired it incorrectly.

 



-- Edited by One1 on Monday 27th of March 2017 07:01:44 AM

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TTRfan


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Lichi wrote:

Unfortunately I will need to heli coil 5 threads that are stripped.... :(

As I need to order them and take minimum ten days to arrive, I don't want to miss the size. Do you think M6*1.25  would be ok?

Actually thread length is 1.3 but I cannot find inserts of this size. Or would be better 1.5 and drilling deeper?

Can you help me to double check this info please?

It is worth investing in an M6-1.00  thread repair kit as this thread is common on the TTR such as all the case bolts, etc.  It is possible to but more expensive types of thread repair kits but I have always used the Recoil kits with 100% success. Try to keep to standard original thread pitch wherever you can.

I think Brian is right about a too long camshaft sprocket bolt causing your damage.

Brian

Recoil helicoil kit 1.jpg

Recoil helicoil kit 2.jpg



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