[bigvander]

Since I can't seem to find how to post a new topic on this forum, I guess I'll just reply to this one!

I just rebuilt my Polaris 700 engine due to a failed end bearing - new SPI pistons, new rods with upper and lower bearings, all new main bearings, and cylinders honed. Basically everything but the crankcase and jugs are new. The crank was rebuilt by a mechanic but I did everything else. I followed the procedures in the manual very carefully and made sure that the ring gaps were within spec (just over minimum). After reassembling everything I went to test start the engine. I was extremely surprised to see how hard it turned over (manual pull, not electric). The engine had 9000 miles on it so it was pretty loose prior to the rebuild but I can't believe how hard it pulls now. It runs well so far and started after the second pull. I really need to hang on to the handle when pulling or it will get ripped out of my hand. I'm wondering if this tightness is normal for a new engine. I did a compression test and it read 110-115 psi, which seems low/normal. I was expecting a much higher reading based on how hard it pulled. Is it normal for a new engine to be that tight? What could be causing this if it isn't normal? Thanks!

 

[BC_Dan]

Of the engines I have had to work on, none of them were hugely excessive to turn over. Are you getting oil?

You may want to consider adding some oil to the gas to make sure there's adaquate lubrication during break in. Don't use synthetic, if you do, the rings will take forever to seal.

 

[burnoutking]

I know a strong 800 is hard to pull over, and have seen as much as 155 psi on a good rebuild. 145-150 is average. Not sure about the 700's , but your compression readings sound low. Should probably still be close to or over 140. Compression tester could be off, or if it is the push/hold in type, it may be leaking past. I like to use the screw in type when wanting accurate readings.

If it starts good, runs good, has lots of power, probably not much too worry about. Compression is probably higher than what you tested, especially if it is hard to pull and kicks back like you say.

 

[bigvander]

BC_Dan - I am getting oil. I oiled the bearings before installing in the crankcase plus oil the cylinder walls. I had a few bubbles in the oil lines due to new pump and lines and they are moving. I also tested the check valves on the case and those opened at 2.5 psi. Based on these indicators I assume that it is getting oil.

I did add Amsoil Interceptor to the tank already at a 40:1 ratio. Guess it is too late.

burnoutking - I was surprised at the low reading as well although the rings are not even close to being seated yet. I used a threaded compression tester - I hand tightened it on, left the other cylinder with no plug, and pulled until the needle stopped. I have seen many testers give different readings on the same machine so I hope that this one is just inaccurate. Is there a certain procedure to do a compression test or did I do it correctly?

The cylinder walls weren't perfect by any means. I could see some hatch marks yet on one but the other had a few minor scratches. Based on the age of the machine and the price of new cylinders (or replating nicisil), I just had them honed.

I was surprised at how fast the coolant heated up. I guess it doesn't take much but I am just hoping that it's not getting too hot. I don't have the clutch on yet so I could feel the PTO end; it was hot to the touch. Is that supposed to get that hot? I wasn't really getting on the throttle at all based on there being no clutch, I just wanted to see if it would run okay.

Thanks for the feedback!

 

[BC_Dan]

Test the compressor on another sled that is running well. If it reads low, it could just be the tester.

The whole engine will get up to at least the temp of the coolant. If the coolant was 120+, the engine will be that temp (or hotter!). That's pretty hot to touch with bare hands.

With the plugs out, rotate the clutch by hand and see if it's smooth to turn over. It should be pretty smooth. If it's difficult, you may have internal issues.

 

[bigvander]

I am supposed to get my clutch back sometime this week so I'll give that a try. I was also told that the engine may turn over a little harder without the clutch installed.

Thanks BC_Dan

 

[ZRNUT]

When you are doing the Comp test are you doing it at WOT? this would cause you to have a lower Comp if it isn't being done.

 

[ZRTEETH]

Back to the tight engine. I have a jig made up to rebuild 1,2 and 3 cylinder cranks. I have done quite a few, as well as complete engines. Sometimes new crank bearings will cause the engine to be stiff until it breaks in. Its hard to say what is tight without being there, but depending on who made the bearings will determine how tight the engine is during the breakin period. I have pulled bearings out of the box and had them spin free as can be, but then i've had some stiff as can be which makes then engine stiff for the first 100 or so miles. Usually factory bearings spin free, but aftermarket bearings tend to be stiff for a while. Thats why when you get a new sled they are easy to pull start. As long as you did everything by the book including your torque sequence for the crank case bolts and it runs fine i wouldn't worry about it unless it hurts your arm to pull it. If thats the case then maybe there is a problem.

 

[bigvander]

No I didn't do the comp test at WOT. How does that affect the compression?

The new bearings are Koyo, which is what was taken out as well. The old bearings did spin much more freely but also made noise. The new bearings do spin slower so that may be some of the cause.

I did follow the torque sequence and did them in 3 stages with a high quality torque wrench.

No it doesn't hurt my arm, I'm just concerned about damaging something. I don't want to do that job again

 

[BC_Dan]

With the carbs wide open, more air is available on each turn of the engine to make compression. If you pulled the rope until the needle stopped, it probably won't make a difference. It's worth a try, though.

 

[bigvander]

I can turn the crank by hand very easily even without the clutch. I put the clutch on and it pulls over normal now. Crazy how much difference that makes.

I have another problem. I got out for a short test ride tonight and I'm leaking gas from where the carb boot meets the reed frame, or where the reed frame meets the intake on the engine. There was gas dripping from each boot on the bottom. Could I have overtightened those bolts? Can I put a bead of high temp silicone to help seal it?