1980 PE 175 motor in a 1980 RM 125 frame!
5:36 pm May 14th, 20121980 PE 175 motor in a 1980 RM 125 frame – don’t believe everything you read on the internet!
Sure, it seemed like a good idea – little extra motor in a chassis that I liked. Reading through the message boards it had all of the earmarks of an easy conversion.
—Motor bolts right in
—Transmission from 1980 RM 125 drops right into the PE 175 cases (for a close ratio transmission)
—Can use a variety of pipes – 1980 RM 125, 1981 RM250, 1983 RM 250, and of course, the PE 175 pipe
—Silencers abound for this project – and all bolt up perfectly to hang the side panels.
So, here is my saga, with pictures to prove that what I am saying actually happened.
Getting a rolling chassis for this project was very straightforward. We used a 1980 RM125 frame, bolted up a 1984 RM250 43mm, dual leading shoe front fork situation (had to press out the 1980 RM125 stem and press it into the 43mm trees), and Works Performance shocks out back. The swing arm is a 1979 RM125 unit with the tabs (the tabs that would have held the roller) ground off and a 1980 RM250 swing arm chain slider bolted in place. Front wheel is a stock 1984 RM250 unit, and the back is a 1981 RM250 hub with Buchannan stainless steel heavy duty spokes laced to an Excel rim. Air box is a stock 1980 RM125 box with a new boot. Controls include new Renthal bars and 1984 RM250 OEM perches and levers. Vintage Suzuki provided new seat foam and cover, all stapled to a stock 1980 RM125 seat pan. Plastics were purchased from DC Plastics, with the preprinted number backgrounds by Bad Brush Graphics.
Once the chassis was sorted Gary and I focused on the engine. We started with a 1980 PE 175 complete motor that I purchased off of eBay. Upon disassembly we found that the motor was on its first bore and had never been split apart. The crank was then completely rebuilt with OEM parts and the cylinder was sent out for a bore to match the new 1st over Wiseco piston. New Boyesen reeds were installed on the case reed block.
With the motor split apart the transmission transplant began. We had a large selection of transmissions from 1979 and 1980 RM125s in the shop (from other projects). Gary dug through all the shafts, gears and forks to find the best of each. All of the components slipped into the PE 175 cases without issue. The shifter drum, forks – everything – lined up perfectly. We did not know it at the time, but this was the only piece of information that I gathered that was correct.
After the cases were bolted back together Gary and I started to assemble the parts necessary to complete the clutch side of the motor. First issue we had to solve was the clutch basket and primary gear selection. The RM 125 and PE 175 baskets and primary gears are significantly different. The only combination we found that worked was the PE175 basket and primary gear. I did have a panic moment when going through the combinations as I had misplaced the PE175 primary gear so nothing was matching up - until I found it in my pile of stuff….
So, now the primary gear, clutch basket, idler gear and kick start all matched up. Next step – inner clutch hub assembly. The PE175 hub did not fit – the splines on the input shaft were different – because we used a RM125 transmission! Dug around and found a good inner clutch hub from a 1980 RM125 and it slid right on – except that the hub was one plate set less than the PE175 basket. Ugh.
Gary and I dropped in new drive and driven plates, and then installed a RM125 pressure plate with new OEM springs. All looked good.
Next we dropped in the best looking shift shaft we could find. I was under the impression that the RM and the PE shift shafts are the same – of course, they are not. What we found when test fitting the RM shafts is that the small tail (that holds the shift shaft engaged on the dogs through contact with the clutch cover) is not long enough. Searching through all my parts revealed that the original PE shift shaft was lost. Amazing – Suzuki still had them available, so we ordered one.
When the shaft came in we found that there were actually 2 variables – the length of the tail, AND, the length of the shaft itself. Seems the width of the PE frame was wider than the RM frame. This brand new shaft stuck out of the case much too far to work in the RM frame. More digging in various boxes ensued and we found that a shift shaft from a 1977 RM125 was the correct length, but had a tail that was just a tad too long. After some careful grinding the shift shaft went into the cases and the clutch cover was secured.
Gary insisted at this point that we pressure test the motor. I was a skeptic – I mean, come on, the motor looked great when we pulled it apart and no one had ever been into the motor! It should be fine. However, Gary was right. When we did a pressure test on the bench we found 3 tiny leaks on the clutch side of the cases. All 3 pinholes were at the center of the casting marks, just like with all of our RM cases. Some JB weld to the rescue, and the second pressure test showed we had an air tight motor.
Finally, time to wedge the motor into the frame. I prepared the original aluminum front motor mounts and assembled the best bolts (and new locknuts) for the engine mounts. Gary and I lifted the motor into the frame only to find that while the front lined up and was the correct width, the rear of the motor was 5 mm too wide. Gary greeted this sight with a loud, “Joe, REALLY?”
Okay, I swear I did test fit a set of empty cases into the frame months before this event. I will admit that it is bit fuzzy if I test fit the CORRECT set of empty cases. My workbench at the time looked like a bomb had gone off, scattering various RM and PE motor parts all around (note above where I struggled finding appropriate RM or PE parts as we were assembling the motor). So, in all honesty, it looks like I took an empty RM case set and found that RM cases do fit inside RM frames. Not very helpful, I know.
After much eyeballing and measuring we decided to take the 5 mm off of the clutch side of the motor. It appeared that the sprockets would line up best this way and that there was plenty of meat on the motor cases to take off the necessary 5 mm. In looking back, the correct way to do this would have been to cut the motor mount tabs off of the frame on the clutch side and move them 5 mm.
After spending quite a bit of time filing down the cases to the correct width, the motor slid into place. Gary and I spent a good amount of time then making sure the rear and front sprocket would line up. The final decision was made to run the countershaft sprocket on the motor with the small ridge facing in towards the motor.
NEXT INSTALLMENT – what we ran for electronics, carb and exhaust!
Sure, it seemed like a good idea – little extra motor in a chassis that I liked. Reading through the message boards it had all of the earmarks of an easy conversion.
—Motor bolts right in
—Transmission from 1980 RM 125 drops right into the PE 175 cases (for a close ratio transmission)
—Can use a variety of pipes – 1980 RM 125, 1981 RM250, 1983 RM 250, and of course, the PE 175 pipe
—Silencers abound for this project – and all bolt up perfectly to hang the side panels.
So, here is my saga, with pictures to prove that what I am saying actually happened.
Getting a rolling chassis for this project was very straightforward. We used a 1980 RM125 frame, bolted up a 1984 RM250 43mm, dual leading shoe front fork situation (had to press out the 1980 RM125 stem and press it into the 43mm trees), and Works Performance shocks out back. The swing arm is a 1979 RM125 unit with the tabs (the tabs that would have held the roller) ground off and a 1980 RM250 swing arm chain slider bolted in place. Front wheel is a stock 1984 RM250 unit, and the back is a 1981 RM250 hub with Buchannan stainless steel heavy duty spokes laced to an Excel rim. Air box is a stock 1980 RM125 box with a new boot. Controls include new Renthal bars and 1984 RM250 OEM perches and levers. Vintage Suzuki provided new seat foam and cover, all stapled to a stock 1980 RM125 seat pan. Plastics were purchased from DC Plastics, with the preprinted number backgrounds by Bad Brush Graphics.
Once the chassis was sorted Gary and I focused on the engine. We started with a 1980 PE 175 complete motor that I purchased off of eBay. Upon disassembly we found that the motor was on its first bore and had never been split apart. The crank was then completely rebuilt with OEM parts and the cylinder was sent out for a bore to match the new 1st over Wiseco piston. New Boyesen reeds were installed on the case reed block.
With the motor split apart the transmission transplant began. We had a large selection of transmissions from 1979 and 1980 RM125s in the shop (from other projects). Gary dug through all the shafts, gears and forks to find the best of each. All of the components slipped into the PE 175 cases without issue. The shifter drum, forks – everything – lined up perfectly. We did not know it at the time, but this was the only piece of information that I gathered that was correct.
After the cases were bolted back together Gary and I started to assemble the parts necessary to complete the clutch side of the motor. First issue we had to solve was the clutch basket and primary gear selection. The RM 125 and PE 175 baskets and primary gears are significantly different. The only combination we found that worked was the PE175 basket and primary gear. I did have a panic moment when going through the combinations as I had misplaced the PE175 primary gear so nothing was matching up - until I found it in my pile of stuff….
So, now the primary gear, clutch basket, idler gear and kick start all matched up. Next step – inner clutch hub assembly. The PE175 hub did not fit – the splines on the input shaft were different – because we used a RM125 transmission! Dug around and found a good inner clutch hub from a 1980 RM125 and it slid right on – except that the hub was one plate set less than the PE175 basket. Ugh.
Gary and I dropped in new drive and driven plates, and then installed a RM125 pressure plate with new OEM springs. All looked good.
Next we dropped in the best looking shift shaft we could find. I was under the impression that the RM and the PE shift shafts are the same – of course, they are not. What we found when test fitting the RM shafts is that the small tail (that holds the shift shaft engaged on the dogs through contact with the clutch cover) is not long enough. Searching through all my parts revealed that the original PE shift shaft was lost. Amazing – Suzuki still had them available, so we ordered one.
When the shaft came in we found that there were actually 2 variables – the length of the tail, AND, the length of the shaft itself. Seems the width of the PE frame was wider than the RM frame. This brand new shaft stuck out of the case much too far to work in the RM frame. More digging in various boxes ensued and we found that a shift shaft from a 1977 RM125 was the correct length, but had a tail that was just a tad too long. After some careful grinding the shift shaft went into the cases and the clutch cover was secured.
Gary insisted at this point that we pressure test the motor. I was a skeptic – I mean, come on, the motor looked great when we pulled it apart and no one had ever been into the motor! It should be fine. However, Gary was right. When we did a pressure test on the bench we found 3 tiny leaks on the clutch side of the cases. All 3 pinholes were at the center of the casting marks, just like with all of our RM cases. Some JB weld to the rescue, and the second pressure test showed we had an air tight motor.
Finally, time to wedge the motor into the frame. I prepared the original aluminum front motor mounts and assembled the best bolts (and new locknuts) for the engine mounts. Gary and I lifted the motor into the frame only to find that while the front lined up and was the correct width, the rear of the motor was 5 mm too wide. Gary greeted this sight with a loud, “Joe, REALLY?”
Okay, I swear I did test fit a set of empty cases into the frame months before this event. I will admit that it is bit fuzzy if I test fit the CORRECT set of empty cases. My workbench at the time looked like a bomb had gone off, scattering various RM and PE motor parts all around (note above where I struggled finding appropriate RM or PE parts as we were assembling the motor). So, in all honesty, it looks like I took an empty RM case set and found that RM cases do fit inside RM frames. Not very helpful, I know.
After much eyeballing and measuring we decided to take the 5 mm off of the clutch side of the motor. It appeared that the sprockets would line up best this way and that there was plenty of meat on the motor cases to take off the necessary 5 mm. In looking back, the correct way to do this would have been to cut the motor mount tabs off of the frame on the clutch side and move them 5 mm.
After spending quite a bit of time filing down the cases to the correct width, the motor slid into place. Gary and I spent a good amount of time then making sure the rear and front sprocket would line up. The final decision was made to run the countershaft sprocket on the motor with the small ridge facing in towards the motor.
NEXT INSTALLMENT – what we ran for electronics, carb and exhaust!
