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Determining stroke and ports drilled
#1
Ok you are out at the local flea market or swap meet and focus on some eye candy. What looks to be a Mac chainsaw is in you view. From the three common shrouds you have narrowed it down to a kart style saw motor. But its really dirty, or missing the air filter cover. Maybe is not even stamped. That does seem to be common. Maybe it is identified, but you are not sure the specs on that particular model. What can you do?

Be it a fixed or removable head isnt so much a concern as is wanting to know the stroke and what ports have been drilled. Here are a few tips that can make it easier to identify. This covers the smaller displacement models. Either 80, 87 or if you are really feeling lucky one of the less common 90.5cc models.

You can use these visuals to identify the saw when it is completely intact with the shrouds and guard in place. Just the muffler needs to be removed. 

First lets confirm what exhaust ports it has. Most of the time it is easy enough to remove the arrestor or, if equipped, with a muffler. These bolts are not usually too tight so they cant be removed easily. The seller shouldnt have a problem with you looking to make sure the piston and bore are in decent shape. That is if he wants to sell it.

[Image: attachment.php?aid=4349]

This is obvious. The center port is not drilled. If this is the case, on your new found gem, it is guaranteed the third port induction is not drilled either. Period. The reason for this is simple. Those three small ports have to be drilled thru the center exhaust port. No center exhaust port, no third port induction.

It is also very and most likely if the saw in question does not have the center exhaust port drilled, then the two outside intake ports are not drilled either. Without one then no reason for the other.

[Image: attachment.php?aid=4350]

So long as we are staring at the exhaust ports, another thing you can focus on. This is not as definitive as the previous mentioned, but will help narrow down the possibility of the third port induction being drilled. If you notice there is a hickey on the left side of center exhaust port. It is not because of the exhaust port being drilled. It is tooling marks left from the third port induction on this block. These marks are most prominent on the left side. Right side is sometimes visible, but to a much lesser degree.

On later model blocks this is seen much more so than early models. Usually early blocks have little or no obvious tool marks at all.

[Image: attachment.php?aid=4354]

The next thing you can help identify is what stroke this saw has. For the 80 and 87cc models is fairly easy to spot. Turn the crank to put piston all the way down at bottom dead center. Roll the crank a little bit back and forth to confirm this. Now look here, you can see the top of piston sticking up just about 1/16 of an inch. This will confirm the engine has a stroke of 1 3/8". Maybe not what you were wanting? Or you are ok with the shorter stroke. If your saw is confirmed to be the 1 3/8" stroke then will also have a 2 1/8 bore. Always, unless it has been bored oversize.

You may also notice the little hickey on this block too. Not nearly noticeable as the other block tho. This block is several years older.

[Image: attachment.php?aid=4351]

Here is a different block. Piston is at bottom dead center. But you can not really see the piston sticking up like the other one. It is nearly flush with bottom of exhaust port. If this is the case, the stroke will be 1 1/2 inches. This is also similar to what you would see on the larger 100 an 103 cc saw engines too. But those have a much easier way to identify stroke. We are focusing on the smaller 80, 87, and 90.5  cc models here.

It is with much probability if stroke is 1 1/2", like above, the bore is also 2 1/8". But there is one known saw with the 1 1/2" stroke that has  a 2.165" bore. The elusive model 450. It is covered here in more detail.  HERE

[Image: attachment.php?aid=4352]

Finally we get to a simple visual confirmation if all six or only four of the intake ports are drilled. On back side of block right next to exhaust ports will be blank like shown here. You see where two intakes have been drilled and plugged. But the right side is still blank. If blank, no port. So only the four of six intake ports are drilled. No biggie tho because a cool fixture floating around out there that can put those missing ports where they need to be just like factory.


[Image: attachment.php?aid=4353]

What you really want to see is the recess like on the other drilled ports as seen here. There is a plug pressed in that covers over the drilled port. If this is here then all six intake ports are present.

Thats enough excitement for one day. Hope this helps.


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#2
I also have not found the 80cc saws with the steel insert for the PTO bearing.
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#3
(12-07-2019, 03:19 PM)steve welte Wrote: I also have not found the 80cc saws with the steel insert for the PTO bearing.

There are several models. The 1-52 and 1-53. Also the 300, 380, and 440. The earlier models are stamped 57965 and 53563. Superceded by 53563A.
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