ST G 21 dissasembly
09-28-2003 | 07:56 PM
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From: Ocala,
FL
ST G 21 dissasembly
Hi Bill,
This is a follow up to my post of 09/24. I was able to remove the drive washer by using a modified battery post puller. However I still am unable to remove the piston/con rod assembly. As I stated in my first post I have removed the cylinder liner but I cannot get the con rod to clear the crankshaft journal. There are 2 wrist pin bosses on the inside of the piston that will not allow the con rod to be lifted enough to clear the CS journal. I have two O.S. engines that come apart using your procedure but this ST just won't do it. Any suggestions would be appreciated. The engine once again is a ST G 21, disp. .46 and has the following cast into the rear cover: CA 35/3.
Thank you,
Don
This is a follow up to my post of 09/24. I was able to remove the drive washer by using a modified battery post puller. However I still am unable to remove the piston/con rod assembly. As I stated in my first post I have removed the cylinder liner but I cannot get the con rod to clear the crankshaft journal. There are 2 wrist pin bosses on the inside of the piston that will not allow the con rod to be lifted enough to clear the CS journal. I have two O.S. engines that come apart using your procedure but this ST just won't do it. Any suggestions would be appreciated. The engine once again is a ST G 21, disp. .46 and has the following cast into the rear cover: CA 35/3.
Thank you,
Don
09-29-2003 | 09:30 AM
#2
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RE: ST G 21 dissasembly
Once the liner's removed, and the crankshaft is fully seated against the rear bearing, the connecting rod can only come off by sliding it aft, off the crankpin. Sometimes it's a bit tight, and you'll have to pry it a little bit. We use curved pliers to do the job. Others have used a large carriage bolt, putting the head of the bolt under the rod and against the crankshaft. The rod will 'pop' off.
Getting it on is much easier.
Getting it on is much easier.
11-11-2003 | 08:52 AM
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From: Noordwijk ZH, NETHERLANDS
RE: ST G 21 dissasembly
Hi Bill and Don, I have exactly the same problem and I would like to have some more info on how to dismount the 21/46 conrod from crankshaft.
As a matter of facts I have used the described procedure too on other engines which do not have a ringed piston, and I suceeded in disassembling a ST 60 and a G21/40 by removing the wrist pin beforehand, using the existing hole in the back of the crankcase (the one with a threaded plug in the G21, simply open to the external on the ST60).
Am a little reluctant to try to remove the liner and try to pry off the conrod in the first instance, because I would really like to avoid the 2 very easy troubles: first of all you will very likely dent the conrod in the process of lifting it with pliers or bolts, and second thing it is very easy to break the ring once you have removed it from the liner with the piston still in place. And when the liner is off and the piston/conrod are still connected to the crankshaft, there is no way of putting it back without removing (read: breaking) the ring.
The presence of the hole suggested me that the way to dismount the engine would be that of lifting the liner slightly in order to expose the wrist pin, align the pin with the hole and then, after heating the entire motor, tap it from the back with a rubber hammer and have the pin simply fall off the piston. At this point the conrod will really come off the crankshaft with no effort at all. As I said it did work twice, but not on the nice 21/46 that I am dealing with now.
On the other side it might well be that the only reason for having the hole in the crankcase back is that of allowing to insert the wrist pin in place during engine assembly, i.e. after having the ring properly seated on the piston and the ringed piston inserted in the liner.
Well, did the suggested removal procedure work without any broken/dented parts ? In this case I might try to apply it as well and risk again to break only the ring.
Thanks in advance
Gianni
As a matter of facts I have used the described procedure too on other engines which do not have a ringed piston, and I suceeded in disassembling a ST 60 and a G21/40 by removing the wrist pin beforehand, using the existing hole in the back of the crankcase (the one with a threaded plug in the G21, simply open to the external on the ST60).
Am a little reluctant to try to remove the liner and try to pry off the conrod in the first instance, because I would really like to avoid the 2 very easy troubles: first of all you will very likely dent the conrod in the process of lifting it with pliers or bolts, and second thing it is very easy to break the ring once you have removed it from the liner with the piston still in place. And when the liner is off and the piston/conrod are still connected to the crankshaft, there is no way of putting it back without removing (read: breaking) the ring.
The presence of the hole suggested me that the way to dismount the engine would be that of lifting the liner slightly in order to expose the wrist pin, align the pin with the hole and then, after heating the entire motor, tap it from the back with a rubber hammer and have the pin simply fall off the piston. At this point the conrod will really come off the crankshaft with no effort at all. As I said it did work twice, but not on the nice 21/46 that I am dealing with now.
On the other side it might well be that the only reason for having the hole in the crankcase back is that of allowing to insert the wrist pin in place during engine assembly, i.e. after having the ring properly seated on the piston and the ringed piston inserted in the liner.
Well, did the suggested removal procedure work without any broken/dented parts ? In this case I might try to apply it as well and risk again to break only the ring.
Thanks in advance
Gianni
11-11-2003 | 10:26 AM
#4
My Feedback: (11)
RE: ST G 21 dissasembly
If your engine has the hole in the back of the case, then you slide the liner up to expose the hole, turn the engine to align the wristpin with the hole, and slide out the wrist pin. If the engine doesn't have the hole, you have to remove the liner and then 'pop' the rod off the crank.
The modern SuperTigre ringed engines no longer have the hole in the case. When you replace the liner, you have to mount the piston/rod assembly on the crank, align the piston ring so that the ring gap is at the pin in the ring groove, heat the case, and carefully slide the liner down over the piston. You have to make sure the piston's absolutely straight in the liner. The bottom of the liner has a bevel to compress the ring as the liner slides down over the piston. You may have to turn the liner a bit to get the ring to compress. Many other engines go together the same way.
The modern SuperTigre ringed engines no longer have the hole in the case. When you replace the liner, you have to mount the piston/rod assembly on the crank, align the piston ring so that the ring gap is at the pin in the ring groove, heat the case, and carefully slide the liner down over the piston. You have to make sure the piston's absolutely straight in the liner. The bottom of the liner has a bevel to compress the ring as the liner slides down over the piston. You may have to turn the liner a bit to get the ring to compress. Many other engines go together the same way.
