OS Surpass 52 Four Stroke OVERHAUL
BY: Mark Fuess

It's show-time!
Every overhaul bigins with dismantling the engine. Carefully dis-assemble the engine and keep the parts in a container. Once it is completely dis-assembled, each and every part needs to be cleaned to perfection and returned to the container. When all the parts are clean you can inspect the parts to determine which ones need to be replaced. All gaskets (including the head gasket) and O-rings are considered expendables, and should be discarded.

The minimum required replacements are; Gaskets, O-rings, and other Seals. You may also need; bearings, piston ring, and other hard-parts as well. Be prepared to spend some money on the overhaul as needed, however some engines are not economically prudent overhauls. Meaning that, at some point the cost of replacement parts will be nearly equal to, or greater than the price of a new engine. A decision has to be made.

About bearings:
There are many grades of bearings available for every engine and priced from a modest $10.00 to over $80.00. If your engine happens to be a really nice one like the 52 Surpass or similar it may be worth investing in better bearings. A high quality set of stainless steel bearings will cost about $35.00 a set.. That's less than what OEM bearings cost at your local hobby shop.

For this overhaul I decided to use Boca Bearings Ceramic Lightning Series bearings. They are Lighter, Stronger, and smoother than conventional bearings. Click on the LOGO to see the bearing selection for your engine..

About hard-parts:
Your piston ring may be OK, however it may or may not re-seat after the overhaul. I'd replace it and remove all doubt. If you need additional parts I would factor in the total cost of the overhaul and weigh it against the price of new engine before you go any further.  

You will Need:
A clean work surface, synthetic oil, heat source, metric allen wrenches, and replacement parts to re-assemble the engine.

* * * FIRST: Install the crankshaft bearings in the crankcase * * *
NOTE: the photos are an OS 91 but it's identical in procedure

The new front beraing is seated by heating up the crankcase enough for the bearing to drop in without force. A hot-air gun is perfect for this job.

The same method is used to install the rear main bearing. Using the crankshaft to seat the bearings insures perfect alignment. While the engine is still hot, put several drops of oil on the bearings. The heat provides great penetration for the oil. After it cools off rotate the crankshaft to be sure it's smooth.

* * * SECOND: Install the Piston, Rod, sleeve in the crankcase * * *

NOTE: On 52, the piston rod must be installed without the piston. Once the rod is on the crankshaft, you can install the piston, and insert the wristpin through access port .  This may take you a few tries, but it will go in. Do not force it!

I have found that it's much easier to insert the piston in the cylinder leaving the wristpin boss exposed, then install the piston & sleeve into the crankcase.This holds the piston in place while you insert the wristpin AND the piston ring is already comperssed in the sleeve. 

Once the rod is connected lubricate everything again. Notice the rod is at Top Dead Center, this is where is needs to be to install the cylinder.

Lubricate the cylinder inside & outside. While keeping the piston on TDC gently rotate the cylinder back & fourth while inserting it into the jug. The tapered edge in the cylinder will compress the piston ring and the cylinder will slide in smoothly. When it's installed, rotate the crankshaft to be sure it's smooth.

* * * THIRD: Install the camshaft in the crankcase * * *

Rotate the piston to EXACTLY Top Dead Center. This is where it needs to be to install the camshaft. Of all the work done so far, this will make or break your overhaul. So double-check your TDC position BEFORE you set the camshaft.

Here is what the TIMING MARK on the camshaft looks like. When inserting the camshaft, it will rotate slightly because it's a wormgear. It will likely take you a few tries to set it. Again, I must stress that the TDC position on the piston must be correct.

Here is how to TIME the CAMSHAFT: With the Piston at TOP DEAD CENTER, insert the CAMSHAFT where the TIMING MARK is in the Centerline of the tappet guide. It's that SIMPLE!

Confirm your timing is correct, generously lubricate everything and install the cam bearing support with two screws. Rotate your crankshaft several times and check for binding or un-usual roughness.          

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mark.fuess@comcast.net