90cc 2 stroke monsoon motorsports quad compression
#1
03-30-2015, 11:29 PM
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90cc 2 stroke monsoon motorsports quad compression
I started working on a quad that has been sitting since 2008. I worked on it years ago and then built a house and put it on the back burner for 5-6 years. The quad is in great shape, has spark and is complete. The carb has been cleaned. It was stored in a shipping container for most of it's life. The compression test registers between 60-70 psi. This concerned me as my 4 stroke 150cc yamoto registers between 125-140psi.
I am trying to figure out if this thing is worth fixing. The tires are like new and the plastics and seat are in great shape. The starter works, cdi works, carb looks like new when I opened it up and cleaned it. Brakes work too. It has the oil injection. It looks like someone might have put 50 hours on it.
Previously I could never get it running. The guy I bought it from back then had it running poorly when I got it. He though it needed a coil. When I got it home I could never get it going. I happened to buy another quad from the same guy for $400 bucks and he bundled it for $200 bucks.
I have read posts of 90cc 2 stroke motors working fine on 50-60 psi compression, for 2 stroke quads like the polaris. Any input would be appreciated. The carbs for these are about $20 bucks new on eBay.
BTW, I found what looks like a top-end rebuilt for $60 bucks for this motor. Was curious if anyone has rebuilt their own top-end and what the process encompasses.
These little quads are quite fun and if I could fix it for $150 i'd be a happy camper.
Samba
I am trying to figure out if this thing is worth fixing. The tires are like new and the plastics and seat are in great shape. The starter works, cdi works, carb looks like new when I opened it up and cleaned it. Brakes work too. It has the oil injection. It looks like someone might have put 50 hours on it.
Previously I could never get it running. The guy I bought it from back then had it running poorly when I got it. He though it needed a coil. When I got it home I could never get it going. I happened to buy another quad from the same guy for $400 bucks and he bundled it for $200 bucks.
I have read posts of 90cc 2 stroke motors working fine on 50-60 psi compression, for 2 stroke quads like the polaris. Any input would be appreciated. The carbs for these are about $20 bucks new on eBay.
BTW, I found what looks like a top-end rebuilt for $60 bucks for this motor. Was curious if anyone has rebuilt their own top-end and what the process encompasses.
These little quads are quite fun and if I could fix it for $150 i'd be a happy camper.
Samba
#2
03-31-2015, 08:42 AM
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03-31-2015, 11:14 AM
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I found just a piston and ring set for $24.99
It sounds like w/ the compression numbers someone ran it without oil or something. I wonder if the rings would do the job, but if I have to tear it down sounds like I should just spend the extra $30 bucks and do the head.
Since I don't know the torque specs on the head bolts, I'd assume they would be 14-20 ft/pounds or so. That is what many small engine heads are torqued to. From the looks of the rebuilt heads on eBay and such, does anyone have a general idea what these should be torqued to?
Thanks
Sam
Since I don't know the torque specs on the head bolts, I'd assume they would be 14-20 ft/pounds or so. That is what many small engine heads are torqued to. From the looks of the rebuilt heads on eBay and such, does anyone have a general idea what these should be torqued to?
Thanks
Sam
#4
03-31-2015, 05:34 PM
#5
04-11-2015, 10:35 PM
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i've rebuilt the top end
Thanks for the help from here. It was pretty simple. I basically had to disconnect the exhaust, and move the engine back in the frame a couple of inches. Then I was able to get the old head off, and the piston was toast. There was several large indentations in the top of the piston head. The rings looked shot, and validated the poor compression. My next chore is to make sure the oil injection system is actually working before I fire it up. I don't really want to deal w/ pre-mix. The question is how the quad in the first place toasted the piston, possibly over-rev, or bad plug gap, etc. The kit was 60 bucks and it took a few hours. There is a small hose that runs to the carb from the oil injection. I'm thinking of taking the plug out, putting in some oil into the plug hole and running the starter on the quad for a bit until I see some oil eek out of the injection port. The old head did not look too bad. Does anyone on here have any suggestions on how to tell if the engine failed previously from no oil getting into the cylinder? What kind of signs would I be looking for? The rings were definitely shot but not scorched or burnt, just worn down, and the inside of the cylinder looked clean without any real damage.
I was fortunate that the head shipped already looks like it was honed. You could see the cross-hatch pattern inside the whole cylinder on the new head. I had a friend validate who rebuilds 2 strokes.
Hopefully it will run tomorrow, assuming the carb isn't shot. I have spark.
A new carb is $25 bucks or so, so worse case it will be another weekend to see it run. My 10 year old son is quite excited to ride. He had finally started riding my yamoto 150cc by himself.
I was fortunate that the head shipped already looks like it was honed. You could see the cross-hatch pattern inside the whole cylinder on the new head. I had a friend validate who rebuilds 2 strokes.
Hopefully it will run tomorrow, assuming the carb isn't shot. I have spark.
A new carb is $25 bucks or so, so worse case it will be another weekend to see it run. My 10 year old son is quite excited to ride. He had finally started riding my yamoto 150cc by himself.
#6
04-11-2015, 11:19 PM
#7
04-11-2015, 11:31 PM
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oil injection
The oil injection system is a complete PIA to remove on this engine (minarelli 90cc clone). you literally have to get specialized tools to remove some reverse threads on the stator assembly just to remove it.
On the carb, I have been unsure how to cap it. I'd assume I would just get a piece of hose with some way to terminate it so I don't lose pressure outside of the hole that the oil is injected into.
I know many say it's the way to go, but I've also heard some people say it causes excessive oil to enter the crankcase at idle, versus full throttle. The scary thing is that the oil injection on these motors is driven by a stupid plastic gear.
I've also thought about the following if I have to leave the oil pump on the unit -
Run the small line back to the oil injection tank with a bulkhead near the top of it so it still works if I ever changed my mind. If I left the pump in place without any oil I would risk it seizing and causing other issues. That's the situation I am in. I have about $250 into this quad now.
I found a great article on how to prime this thing to see if it still works.
Avoiding a soft seize/oil pump adjustment | 49ccScoot.com Scooter Forums
I am thinking the likely cause of the failure of the engine the first go around was someone not re-priming the oil injection system after running it near-dry.
Thanks
On the carb, I have been unsure how to cap it. I'd assume I would just get a piece of hose with some way to terminate it so I don't lose pressure outside of the hole that the oil is injected into.
I know many say it's the way to go, but I've also heard some people say it causes excessive oil to enter the crankcase at idle, versus full throttle. The scary thing is that the oil injection on these motors is driven by a stupid plastic gear.
I've also thought about the following if I have to leave the oil pump on the unit -
Run the small line back to the oil injection tank with a bulkhead near the top of it so it still works if I ever changed my mind. If I left the pump in place without any oil I would risk it seizing and causing other issues. That's the situation I am in. I have about $250 into this quad now.
I found a great article on how to prime this thing to see if it still works.
Avoiding a soft seize/oil pump adjustment | 49ccScoot.com Scooter Forums
I am thinking the likely cause of the failure of the engine the first go around was someone not re-priming the oil injection system after running it near-dry.
Thanks
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#8
04-12-2015, 07:53 AM
The oil injection system is a complete PIA to remove on this engine (minarelli 90cc clone). you literally have to get specialized tools to remove some reverse threads on the stator assembly just to remove it.
>I don't think so. what's a pia is replacing motor parts cuz a oil pump doesn't work<
On the carb, I have been unsure how to cap it. I'd assume I would just get a piece of hose with some way to terminate it so I don't lose pressure outside of the hole that the oil is injected into.
>A toothpick in the line works, so does a vaccum cap from the auto store<
I know many say it's the way to go, but I've also heard some people say it causes excessive oil to enter the crankcase at idle, versus full throttle. The scary thing is that the oil injection on these motors is driven by a stupid plastic gear.
>It is the way to go. I think opposite as far as oil in the cases..remove that plastic gear<
I've also thought about the following if I have to leave the oil pump on the unit -
Run the small line back to the oil injection tank with a bulkhead near the top of it so it still works if I ever changed my mind. If I left the pump in place without any oil I would risk it seizing and causing other issues. That's the situation I am in. I have about $250 into this quad now.
>once the pump isn't driven you can eliminate the oil lines and tank<
I found a great article on how to prime this thing to see if it still works.
Avoiding a soft seize/oil pump adjustment | 49ccScoot.com Scooter Forums
I am thinking the likely cause of the failure of the engine the first go around was someone not re-priming the oil injection system after running it near-dry.
>Not me. I think it was simply wore out. When there is no oil the piston siezes and will gouge the cylinder/barrel (not head) badly<
Thanks
>I don't think so. what's a pia is replacing motor parts cuz a oil pump doesn't work<
On the carb, I have been unsure how to cap it. I'd assume I would just get a piece of hose with some way to terminate it so I don't lose pressure outside of the hole that the oil is injected into.
>A toothpick in the line works, so does a vaccum cap from the auto store<
I know many say it's the way to go, but I've also heard some people say it causes excessive oil to enter the crankcase at idle, versus full throttle. The scary thing is that the oil injection on these motors is driven by a stupid plastic gear.
>It is the way to go. I think opposite as far as oil in the cases..remove that plastic gear<
I've also thought about the following if I have to leave the oil pump on the unit -
Run the small line back to the oil injection tank with a bulkhead near the top of it so it still works if I ever changed my mind. If I left the pump in place without any oil I would risk it seizing and causing other issues. That's the situation I am in. I have about $250 into this quad now.
>once the pump isn't driven you can eliminate the oil lines and tank<
I found a great article on how to prime this thing to see if it still works.
Avoiding a soft seize/oil pump adjustment | 49ccScoot.com Scooter Forums
I am thinking the likely cause of the failure of the engine the first go around was someone not re-priming the oil injection system after running it near-dry.
>Not me. I think it was simply wore out. When there is no oil the piston siezes and will gouge the cylinder/barrel (not head) badly<
Thanks
#9
04-13-2015, 11:08 PM
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Hooked everything back up. Ran compression test, is around 90 to 100 psi on the new head and piston/ring setup. Previously 65 or so. Added fuel to the tank, blew out all of the lines, and no startup. I don't think I am getting gas. I've cleaned out the carb and aligned the float upside down to be level. Cleaned out all carb passages. Not sure what to do at this point. I ordered a new carb tonight for $20 bucks . I haven't checked the reeds and I'm not really sure what to look for anyways. I have good spark at the plug and am a bit frustrated. Any feedback would be appreciated. I'm going to go with 2 cycle pre-mix going forward. I think the oil injection is shot as I tested for by running the motor for quite a while w/ the electric start and pressed down the throttle, no oil came out even after priming the pump.