TDR Project – Engine Top End Strip Down | The Lifestream of Brian blog

Just to clarify, Mildred’s previous owner had replaced the original TDR250 engine with a TZR250 (2MA I think) engine. Even though it was running well before the start of this project I need to strip it down to have the cases vapour blasted. Once vapour blasted I am not sure whether I will paint the cases black, grey or clear coat them. I guess I’ll decide once I get the cases back from vapour blasting.

This is the first time I have ever stripped a 2-stroke engine and I’m sure that I will learn a lot along the way.

Here is how the engine looked with it removed from the frame:

Engine - Front

Engine - Right

Engine - Rear

Engine - Left

Engine - Above

The aim for this stage was to remove the head cover, barrels and pistons but the first task was to drain the transmission oil and any remaining coolant from the engine. The fact that it was -1C outside did not help as ideally you would have a warm engine before draining the oil but as the engine is out of the frame there was no option but to do it cold. I carefully positioned the engine on my cheap Wickes “workmate” and left it to drain whilst I went for a cup of tea.

Draining Oil

The following steps were taken to strip down the top-end:

A. Remove spark plugs. Note to self: I really must buy a spark plug spanner.

Spark Plugs Removed

B. Remove water pump.

Water Pump Removed

C. Remove head bolts/nuts in order. Start with the highest numbered fastener and loosen each one in turn by a 1/4 turn before removing all of them. 4 of the nuts were dome headed and these were fitted with copper washers. I’m not sure why this is done but I will replace these with new copper washers when I put it all back together. One of the studs came out completely but as they all need to come out this is not a problem.

Head Fasteners Removed

D. Carefully remove the head to expose the barrels and head gasket which is sheet metal. It also has a handy marking indicating which side should be in contact with the head.

Head Removed

With the head off it became apparent that the left cylinder had let go at some point in its history. The head was pitted as you can see in the 2 photos below:

Head Pitting/Damage

Left Head Close Up

E. Remove the power valve link between the barrels.

Power Valve Link

Power Valve Link Removed

F. Remove the barrels. The lower right (right barrel) and lower left (left barrel) nuts required careful removal as they are tight to the barrels.

Right Barrel Removed

Left Barrel Removed

G. Remove the pistons. These are secured by circlips which should be removed with caution to ensure that they do not drop into the crankcase. With the pistons removed I could see that the left cylinder has definitely had some repair work in the past. The piston crown is marked with “0.50″ which I am assuming means that the barrel has been re-bored and an oversize piston has been fitted. The right piston is marked with “0.25″.

Right Piston

Left Piston

And here’s how the engine looked at the end of the day.

Top End Removed

I will carefully measure all of the top end components to see what needs repair or replacement. I will have to consult people who know far more than me regarding the fact that the left and right cylinders have different bores/piston sizes and it may end up requiring some machining to make them the same, complete with new pistons/rings.