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

TTRfan · Super Guru

Rebuilding a 2005 official UK imported TTR250

TTRfan · Super Guru

I have seen pitted valves before but not quite as bad as these. The exhaust valves on this engine are too far gone and I will have to replace them. The valve seats look fine so that's a bonus!

Brian

Paul13 · Veteran Member

I hope you keep one for me to purchase in March 2016

Really fancy one of your rebuilds. Ride a 450 Kim at the moment. However another bike in the garage would be great.

TTRfan · Super Guru

I might have finished it by then Paul - possibly smile

The following sequence is a bit basic on how to install new valve stem oil seals so apologies to experienced owners!

Having lapped the valves in, it's now a case of carefully re-assembling the head.

I am using some Kibblewhite VSOs I bought as a job lot recently hence they are blue rather than the traditional Yamaha green..

Valves 001.jpg

I find the easiest way to install them is to keep them straight over the guides by slipping them over the valve stems first.

Valves 004.jpg

It is easy then just to push them down with your finger with the valve stem until you feel them click into place.

Valves 006.jpg

VSOs in place.

Valves 007.jpg

To keep the valves from dropping out I use a block of wood that fits between the two head spigots and a rolled up bit of paper that fits in the combustion chamber. Otherwise when pushing down on the valve tool the valves move down making it difficult to install the collets.

Valves 008.jpg

I only use one part of the valve spring compressor kit and find that I can compress the springs with my thumb enough to pop the collets in without using the cumbersome compressor tool that comes with the kit. I use a non-magnetic screwdriver to press the collets into place.

Valves 009.jpg

I then put the shims and buckets back into their original positions and give them a good lathering of engine oil.

Valves 011.jpg

Next up is to fit the cams and can caps and set the valve clearances.

Brian

TTRfan · Super Guru

Time to check the valve clearances. It's a lot easier with the head off the engine but the procedure is much the same as if the head is fitted except you will have to deal with the timing chain if you find you have to remove the camshafts to adjust the clearances.

Set out the cams and caps in their correct position and have everything nice and clean.

Assemble the cams and caps and torque the nuts up to 10Nm. All of the bolts should be free in their threads so that they torque up properly. Use a thread cleaner on any tight ones if you have one. I got a metric kit which has earned its keep many times over. It is possible to buy individual parts and a 6mm x 1.00 tap and die is really useful for working on the TTR.

Mr Yamaha has kindly marked the TTR's cam caps with I for Inlet and E for exhaust plus a direction arrow on each cap pointing to the RH side of the engine smile

I use a laminated guide with the cam lobe positions and clearance ranges written on it along with an essential bit of kit - a set of metric feeler gauges with individual gauges from 0.02mm to 0.10mm and then in stages of 0.05mm.

I use a spanner to turn each camshaft both ways to compress the valve springs and make sure the valves, shims and buckets are seated properly.

Check the valve clearances with the feeler gauges and make a note of each gap where the feeler gauge slides under the cam lobe easily and is not being forced.

The camshafts can then be removed and any necessary adjustments made using different sized shims. I use a valve tool to pull out the buckets.

The next bit is the interesting part of the exercise! Having noted the respective gaps and checked the size of the existing shims, you need to do a bit of arithmetic to work out what size shim is needed to get the optimal gap. I aim for the midpoint of the range of clearances given in the manual i.e. 0.14mm for the inlet valves and 0.23mm for the exhaust valves.

In my particular case, both inlet shims were 2.00mm and the gap was 0.08mm. To get to the ideal of 0.14mm I needed to reduce the shim thickness by 0.06mm. So 2.00mm less 0.06mm gives a shim thickness of 1.94mm.

The shim kit I use has a variety of thicknesses in 0.05mm increments so the nearest to the 1.94mm shim that I have is 1.95mm which is absolutely fine biggrin

Be careful that you put the new shims into the valve retainer squarely as it's the devil's own job to get one out again if it tilts and you try pushing it in

If you are working with the head installed then you can now replace the timing gear. As my head is off, I have to fit it so that I have access to the inside head bolts before they are covered by the cam gear.

Next up is to install my head biggrin

Brian

TTRfan · Super Guru

Head back on but the cam chain looked to be a bit tired so I decided to fit a new one before torquing down the cam cap bolts.

When I removed the clutch cover I found that one of the case bolt heads had snapped off cry

My friend Rik is a master of the "weld a washer over the sheared bolt/stud to get it out" method so I took the engine to him to get the broken bolt out.

A very simple but effective technique.

Rik put a washer over the remains of the bolt.

And then MIG welded the washer to the stud.

The heat going into the bolt from the MIG welding helps free it up and it was then possible to start to wind it out using a pair of Vise grips on the washer which gives some extra leverage.

It was then a case of winding it all the way out with the Vise grips in the centre to prevent any damage to the gasket edge of the crankcase.

This is what the remains of the bolt looks like.

A little bit of aluminium came out with the bolt from the top of the thread but a quick run down with the re-threader cleaned up the threaded bolt hole and I am pretty sure that a new bolt will torque up nicely biggrin

Onwards and upwards!

Brian

TTRfan · Super Guru

Fitting a new solenoid