elroy,

I hate to ask a dumb question but, did you hone the cylinder while you had it off to port it? This could be the cause of the low compression. I may have missed it in an earlier post, but I'm almost sure you didn't mention honing it. Also what was the piston skirt clearance? It should be around .0012-.0026". The piston ring gap could should be .012-.022". I'd check these before I did any more milling to the head. Like my old shop teacher told me, it's easy to take metal off but it's almost impossible to put it back on.

 

Well, I've been pretty busy last week and this week helping a friend get caught up at his Transmission shop. I don't really work for him, I just help him out. That's why it took me so long to get my quad together. I probably won't get the head shaved again until later this week.

As for my compression only being 125# after taking .040" off the head, I made a boo-boo. After I got done chamfering my ports I took my final measurements to see how I ended up. To my surprise I was alot higher on my exhaust port. I didn't really cut up their so I can't even explain how I raised it. Unless I was measuring my chamfer. I just dunno. According to my math though, I raised it about (.090&quot. That's why my compression didn't come up as far as it should after cutting .040" off the head. All and all though this didn't really hurt me to bad because of the way I have my clutching set up. I have the engagement set higher so I'm not really pulling anything at my lower rpm range. I didn't want to cut anything off the top of my exhaust port, it just happened that way.

As for my skirt clearance and ring gap, No I didn't even check them because my engine was rebuilt about 5 months ago. I'm not saying that they couldn't be out of specs but I guess I have a little blind faith. Outside of the carbon build up that I had on my piston, everything still looked like it did when I put it together 5 months ago.

I didn't work on a customer's quad, I worked on my own. If I would have been working on a customers quad then I would have taken a little more effort in checking all the other areas of the motor besides just cutting the ports. This port job was more of an experiment than anything. I wasn't out to build a race engine because I don't have enough experience in porting. All I tried to accomplish was to get some experience in porting, get a little knowledge as to how it all works and hopefully make it run better. I was able to accomplish all three. This to me was a success. Next time I will take it a step further and do things better than I did this time.

By the way I went for a 40 mile ride Sunday afternoon. My quad ran perfectly. I was riding with a 300ex. We were allways real close in a drag race. He would usually pull away a little off the line and stay just ahead of me the whole way from there. Now, I eat him up off the line and I only see him catch back up with me once we get to the 50 mph mark. He still has a slightly taller top end. So he goes about 3 or 4 mph faster than I can. I will fix this too, in time.

 

I have a question for all you pro engine builders. I origanally had .110" head clearance, so I shaved .040" off. That left me with .070" clearance. I checked my clearance using a piece of solder. I still have all the pieces of solder in the order I've been testing.

Well, I wasn't happy with all the more compression I had(125#) so I decided to take my head back off and get it shaved just a little bit more. I thought I should recheck my clearance again. To my surprise it was back up to .090". I don't understand how it could read .070" clearance on saturday and then read .090" 4 days later. I then took my head off and mic'ed it. It too read .090" when I know it read .070" 4 days before that. This all really confuses me. I also checked it at the shop that shaved my head and their mic's read the same thing. Last I knew aluminum did't grow on its own.

All the readings I take with the solder, I check both sides of my cylinder to make sure I get the same reading twice. Like I've also said, I've saved each and every piece of solder and labeled them from when I tested them. They say the same thing I'm saying.

I ended up taking another .025" off my head. Came home and bolted it on. Checked my clearance again. It was .065", like it should have read. I then took a compression test to see what my reading was here. It was 125#, like it was before. This all is really starting to confuse me a little. As for my comp. tester, it is new. But then again I have never seen it read anything above 125#, even on my car. Maybe it is defective. I still don't understand how my head grew .020". I've ran this through my head a 1000 times and still can't make any sence of it.

My quad seems to be running great. The only thing I can say is that my idle has gone up and I can't get it to go any lower. It isn't that much higher but I can't get it to go any lower. Besides that this thing really rips. I'll have to do some more clutch work to see the full potential. Not to mention the pipe and carb.

 

Try using modeling clay instead of solder . I put some on the piston , turn the engine over , and then cut a strip out with a razor and measure it .

I have no idea why you have readings that vary like that , except for one thing . The angle on the head does not match the dome of the piston . Heads are typicaly a few degrees steeper than pistons, and should be . Check the head with clay , cut out a cross section and observe the difference in degrees . This could explain why your measurements vary .

 

elroy,

You might have to change the pilot jet to get the idle back down to where it was. Try turning the air mixture screw to see if it will change. Turning the screw in will make it richer and turning it out will make it leaner. You really don't want to turn it out, you already have a lean condition. If you turn it all the way in and it still doesn't idle right, you'll need to get a bigger pilot jet. If you're still running the stock jets in yours, try a 45 pilot jet. that should bring the idle down nicely.

 

Mike,

Thanks. I took my 5 year old daughter for a ride yesterday. Before we left, I did as you said and it worked. My setting is 1.5 turns out. I had to turn it almost all the way in to get my idle down. However, my quad doesn't rev as quick out of the hole. The quad still runs the same through out the rest of the throttle range. It just doesn't rev as quick out of the hole. Was the lean condition responsible for giving me such a quick rev? I really liked the way it hit so hard off the line. If I replaced the stock jet to the 45 jet, will this enable me to get that back. Or was that caused only by the lean condition? Another thing I would like to add to this senerio is that I didn't have this high idle after I first put it together. It was just the same old quad sitting there at idle. The high idle only appeared after I put it back together after the heads second shaving. I honestly wondered if I had an air leak but hadn't checked it out yet until after I read your post. I do understand what lean conditions do to motors but it didn't idle like that at first. Why would shaving the head a little more create a lean condtion that would make it idle higher?

As for the whole port job in general, I am so glad I did it. It ended up costing me about $200 to complete it. The benefits I got out of it though where well worth it. I gained a little on my bottom end and a little on my top end(probably get more here with pipe and carb). My mid range is where I really see a difference. It seems to hit its hardest right at my shift point. This is really cool because as my engine is really pooring out the power, it is also shifting into the higher gearing. It easily pulls twice as hard from 0 - 45 mph. That is , if I can keep it from breaking traction. I am currently running 25x13 Wolly Buggers(stock was 24x11) and I am running 14/38 sprockets(stock 13/38). This thing will spin the tires easier than it ever could in its stock form. Not to mention that I've gained about 15 mph over its stock, 50 mph. I will say though, that I've had to do extensive clutch work over the years to make it pull these higher ratios without it taking away from my bottom end or acceleration. And "NO", I did not buy a clutch kit. I built my own "clutch kit". I bought individual pieces.

 

elroy,

Yeah, the non reed machines are like that. I basically did the same thing to my GF's Trailblazer. Only I had to end up replacing the pilot jet and had to rejet the carb completely when I put on the 34mm Mikuni. I replaced the pilot again when I put the U.F.O. in.

There seems to be a bog on these piston ported machines that won't go away unless you run them at a high idle. Something to do with the way they were designed. They were made to be cheap and reliable, NOT a high performance motor (much to our dismay).

You mentioned that you're running a 14 tooth front sprocket, where did you get it? I'm looking for one for my Sport. I'm not so much looking for speed, as I am reducing the wheelspin (same as you). I'd go down to a 34 tooth in the rear if your machine can handle it, if not try one of the newer 36 tooth rears off the 2000 and newer models. I've heard that other people have run 14 tooth front sprockets on their concentric drive machines, but never on the older machines. Is there a problem with swingarm clearance? Thanks in advance.

 

Mike,

I was wrong. I only have 13 tooth up front. I remember reading in a book that my stock sprockets were 13/38. I called up the local Polaris dealer and told him I wanted a one tooth bigger sproket. I now remember getting into an arguement with him about the sprockets because he said my stock sprocket was a 12 tooth. He said the biggest thing he had there was a 13. I wasn't at home to check so I told him to drop it off at my house that night on his way home. Well to my surprise he was right. Mine was a 12. He brought me the 13 and that is what I have on it know. My mind was stuck into thinking I had a stock 13 and went one tooth bigger. The only reason I remembered know was because you got me thinking when I read your post so I had to go count teeth. As I counted I started to remember the whole story.

I'll have to do some more digging around to see about this 14 tooth. I don't see why their would be a problem with swing arm clearance. I do wonder though if their would be enough clearance around the tranny. It would probably clear it but it wouldn't leave ANY room for error. The question more pressing is, would it be sized right for the shaft? This is what I'll have to check on. I know I would have grind the hole in my side plate that the sprocket slides through in order to get a 14 tooth in there.

Sorry to get your hopes up. Like I said I remebered wanting a +1 sprocket when I thought I had a 13. Know I remember it was a 12. I'll check with Polaris tommorrow about this 14 tooth.