san francisco website design company

Removing and replacing a cylinder head on a Yamaha TTR250

There is quite a lot of work involved and it is essential that you have the workshop manual to hand for full details of the procedures, torque settings, etc.

However, the manual expects you to be removing and replacing the cylinder head as part of a full strip down and that is not always going to be the case.

This pictorial guide assumes you ONLY want to deal with the cylinder head and is just to help you along the way.

Tools needed:- I used just about every tool I had in the toolbox - and others beside!

Parts/supplies: Head and base gasket set and cylinder base O ring.

Before you start, remove the seat and petrol tank and power wash the area above the cylinder head so that no dirt can drop into the engine when it is being dismantled.

Then make sure that the bike is safely on a stand and at a comfortable working height - if at all possible. Make sure the floor and working area is clean. I tend to rob the recycling bin of old newspapers and lay them around to give a clean absorbent surface on which to put down any parts removed.

First step after getting the bike on the stand is to . Then loosen the Jubilee clip on the shock reservoir and move that back out the way.

You now have access to remove the exhaust down pipe and the head steadies (arrowed).

Next remove the three Allen bolts and take off the cam cover being careful not to damage the rubber gasket.

No kick start on this TTR so I put the engine in 6th gear and turned it to the TDC mark using the rear wheel. TDC is the SINGLE mark and not the H shaped mark about half an inch away.

Ensure both cam lobes are pointing away from each other (see pic below), and alignment markers are as shown in photo above.

The cams will then be in the correct position for when it comes to putting them back.

Remove the Allen bolts and take out the cam chain tensioner.

I use a bit of wire around the cam chain to stop it falling down into the crankcase. Pack something like a lint-free cloth down below the cam whilst removing each bolt, as you really don't want to have to retrieve it from the crankshaft having let it drop in. That would ruin your day! Remove cloth once bolts are safely out of the way. The bearing caps and cams can then be removed.

The wire is holding the cam chain out of the way securely.

Place the removed cams and caps in the correct order on some newspaper.

In order to access the head retaining bolt at the back of the engine I recommend removing the starter motor which is a fairly simple job. Two bolts plus a nut holding the terminal as arrowed.

The oil pipe is also removed giving clear access to the head retaining bolt arrowed in the picture.

Remove the cylinder head bolts and the head can then be removed.

Another view of the cylinder barrel with the head removed. This is as far as you need to go if you are replacing a head gasket or have other work to do on the cylinder head. In my case this was to Helicoil a stripped thread which isn't accessible with the head in place.

Ideally, you should now check the valve clearances and, if any adjustments are necessary, fit the correct shims to bring the clearances within specifiaction.

At this stage it is worth checking the rear cam chain guide where the tensioner pushes against it. Check the "punch" mark as the guide can sometimes get damaged at this point.  

The head is now being replaced using a new head gasket. It is sometimes a bit of a struggle to get the carb lined up with the rubber inlet manifold but this is easily remedied with a bit of friendly persuasion with a large flat blade screwdriver or similar.

Ready to replace the head bolts.

To save messing up the manual, I jot down the head tightening sequence and torque settings on scrap of paper.

All the bits on the trolley (along with the tools needed)  ready to refit!

Be sure to follow the correct tightening sequence and torque to the correct settings as in the manual.

Before replacing the start motor, I just put a bit of silicone lubricant on the rubber seal. Whilst the starter is out, it's a good opportunity to check the condition of the pinion teeth. Mine were perfect - phew!

Replace the terminal nut and two retaining bolts on the starter motor.

Double check the engine hasn't moved and that it is still at TDC i.e. the SINGLE mark and not the H.

Rest the cams back in the head with the markings as shown in the manual. Again. I tend to draw a diagram (arrowed) to save mucking up the manual. When placing the chain back on the sprockets make sure you are tensioning it over the front sprocket.

Replace the caps and carefully torque them up.

This can be tricky! I never seem to have a screwdriver short enough to make replacing the tensioner an easy job and, since taking the pic have made one up. So, using a small screwdriver, turn the tensioner head inside the bolt hole which will pull the spring-loaded tensioner plunger back. Hold the screwdriver in place whilst replacing the tensioner and the 2 bolts holding it in place, and then gently release the screwdriver allowing the plunger to extend. There should no longer be any slack in the cam chain.

Roll the engine forward at least 2 more full revolutions, then check the cam timing again. Better to find out now that it's moved, rather than when it's all back together!

Replace the oil feed pipe on its three banjo bolts using new copper washers if you have them. Otherwise you can anneal the old ones.

Replace the cam cover and the retaining Allen bolts.

Before going any further it is worth checking that you have an oil feed by taking out the check bolt and turning the engine over on the starter with the sparkplug out (but grounded!).

Assuming all OK, the exhaust and head steadies can be replaced.

Tighten everything up including the carburettor retaining circlip and you are ready for a test start.

Recheck everything is tight before starting engine and that you have refitted the oil breather pipe on the cam cover of later engines. Make sure the doors and windows in your workshop are open and start up and run for a short while to check for any oil leaks etc. Listen for any strange noises, and SWITCH OFF immediately if you hear any as you've not finished yet if this is the case. Hopefully you will have no problems.

Job done!

Brian Sussex