CRUSADER 60 REPAIR

This engine was sent in to us by a home builder who has done a fair job of constructing this engine but was unable to get it to run. O.K then, let's take a look and find out why he won't run.

The engine on arrival at our workshop.

Lets get it pulled down and see what's what.

So just before we dismantled the engine we did a quick check of the compression and found that it was somewhat lacking, not a good sign but nothing that can't be easily rectified.

The back plate intake hole is also a bit large which has given a reduced intake seal area around the intake drum valve so while it looks ok at first glance with nice thick oil once fresh fuel gets involved I can see the seal disappearing rather quickly. I think this part will also need a bit of rectification work.

Having cleaned and rechecked the cylinder parts this is what we found.

Oh dear, it is now apparent that a rebore is required so we will get on and carry out this procedure first.

Once the required tooling has been produced for the rebore operation we will finish machining the replacement piston and carry out the final fitting to the cylinder.

Here we have the main case and crankshaft cleaned and reassembled ready for the refinished cylinder and piston assembly to go back onto. We also took the opportunity to  tidy up the modification to the inside of the case for some con rod clearance.

Before..........

After...........

Having made all the tooling for relapping the cylinder liner, here's the first pass through which shows the extent of the out of roundness of the bore and the damage caused by the gudgeon pin and piston baffle scoring the bore.

The first pass with the lap was at bore plus 28 microns up to a total clean up of 32 microns.

After removing a total of almost 0.150mm, that's 6 thou", we have a nice and round, clean bore finish that's ready to take a new piston.

Next step is to machine up the new replacement piston and required tooling to mount and final fit it to the restored cylinder liner.

Here's the new piston blank with a few minor modifications from the original drawing, and piston to achieve a much lighter piston.

And assembled back onto the original conrod using the original gudgeon pin only this time it's pressed in and not floating.

Now we will move forward with the final machining of the new piston and fitting it to the newly lapped original cylinder liner.

Final turning the new piston to size.

Having finished the machining of the piston and making the reduction in diameter for the baffle it's now time to machine in the baffle on the piston crown.

Now it's time to lap the new piston to fit the cylinder liner and get the nice bouncy solid compression fit we're looking for.

Here we have the new piston all nicely lapped to size and fitted to the restored cylinder liner.

And all reassembled ready for the back plate to be added once it's sorted.

Now that we have that nice crisp pop over compression that isn't all squishy and wimpy let's get the back plate cleaned up and refitted.

And here we have it all sorted and finally ready for the test stand.

O.K. so where'd that fuel bottle go???

Well it lives, finally.

Quick check of the throttle.

Summary..

There are a number of points that we have addressed in this repair and also a few that were left. We modified the lube hole to the crankshaft man bearing journal as this was not drilled completely and therefore was not allowing any lubrication to the main bearing. We also modified the piston design slightly for weight and vibration reduction. we have left the backplate as it was but would change this area also if we ever decided to build this engine. The squish band is at 3mm which is to much for this engine to produce any outstanding power as the compression ratio is less than ideal but certainly enough for the engine to run, again, this is something that we would change, and recommend any builder to also change if choosing to build this engine. The biggest contributor to the engine not running in the first place was the severe lack of compression at the piston to liner fit. With this rectified the engine ran well enough.