New Piston/Rings seem tight, what does PVC hose connect to?

[Tfastle@aol.com]

I have a couple other posts on this engine but probably best to have new posts for new subjects. 2007 MPT, 350 Robin MCI, received it completely torn down and engine in pieces in a box.

I have the engine reassembled and have a couple of questions. As per an earlier post I had some issues figuring out how the rings went on the pistons but think I sorted that out. With the rings installed it seems a bit tight. By "a bit tight" I mean that when I turn it over by hand (head off) mid stroke is not "very" easy to turn through (not hard though) and there is a very slight dragging noise. This would be the point where the pistons are moving most quickly up and down. I suspect it's the oil ring which is a 3 part configuration, 2 light rings and a spring ring that pushes them out. I gather, especially with new rings, that due to the oil ring spring (middle of the 3), they are quite tight initially (and probably continue to be). My experience is mostly with 2 stroke motorcycle engines and with them when new pistons and rings are installed turning the crank by hand (head off) is very smooth easy and quiet. This one takes more force and, as described, has bit of sound. I am inclined to continue forward and fire it up but, after getting to this point wanted to see if anyone has an opinion on it here and if I might have an issue?

It's the original bore, I did put a cross hatch on it, put in new std piston/ring set, and the end gap on the new comp ring is about .006 . Of course I did coat the sides of the cylinder with oil. With the head installed, timing belt installed and plugs removed, turning it over by hand using the ends of the crank shaft (no fan or clutch) is difficult (have to grip crank very tight and turn with a bit of force). With the fan installed and using that to turn it over it's not difficult at all but there is some drag.

Am I ok or do I have a problem?

Lastly, and what my post was going to be about originally, I see where the PVC hose or tube connects to the PVC valve (MCI so on top) but where where does the other end connect? I thought it must go to something on the air filter plumbing but don't see a place for it.

Once again, sorry for how long this is but it seems better to have too much info than not enough.

Thanks in advance for any input.

[JPonLKN]

Originally Posted by Tfastle@aol.com

I have a couple other posts on this engine but probably best to have new posts for new subjects. 2007 MPT, 350 Robin MCI, received it completely torn down and engine in pieces in a box.

I have the engine reassembled and have a couple of questions. As per an earlier post I had some issues figuring out how the rings went on the pistons but think I sorted that out. With the rings installed it seems a bit tight. By "a bit tight" I mean that when I turn it over by hand (head off) mid stroke is not "very" easy to turn through (not hard though) and there is a very slight dragging noise. This would be the point where the pistons are moving most quickly up and down. I suspect it's the oil ring which is a 3 part configuration, 2 light rings and a spring ring that pushes them out. I gather, especially with new rings, that due to the oil ring spring (middle of the 3), they are quite tight initially (and probably continue to be). My experience is mostly with 2 stroke motorcycle engines and with them when new pistons and rings are installed turning the crank by hand (head off) is very smooth easy and quiet. This one takes more force and, as described, has bit of sound. I am inclined to continue forward and fire it up but, after getting to this point wanted to see if anyone has an opinion on it here and if I might have an issue?

It's the original bore, I did put a cross hatch on it, put in new std piston/ring set, and the end gap on the new comp ring is about .006 . Of course I did coat the sides of the cylinder with oil. With the head installed, timing belt installed and plugs removed, turning it over by hand using the ends of the crank shaft (no fan or clutch) is difficult (have to grip crank very tight and turn with a bit of force). With the fan installed and using that to turn it over it's not difficult at all but there is some drag.

Am I ok or do I have a problem?

Lastly, and what my post was going to be about originally, I see where the PVC hose or tube connects to the PVC valve (MCI so on top) but where where does the other end connect? I thought it must go to something on the air filter plumbing but don't see a place for it.

Once again, sorry for how long this is but it seems better to have too much info than not enough.

Thanks in advance for any input.

I'll answer your second question first...it is a PCV valve (Positive Crankcase Ventilation)...and it connects to the back side of the intake that mounts onto the carburetor. See below, items 22 and 23.

first question...Last time I put one together, I don't recall it being difficult to turn over without the head on, or even with the head on and no plugs. It is heavier to turn than a two cycle as there are less moving parts. Shouldn't be a dragging feel. Are you sure the interface at the crank to rod at the journals was smooth? If there was any issue with either surface, they would feel like they "catch" as you rotate them. That isn't good...needs to be smooth. I'm sure Trig123 will jump in here this afternoon sometime....he could certainly give you a better feel for what it should feel like once it is together. I have much less experience in that regard.

[cart around]

I also think you need to check the manual for proper end gap. .006 sounds too tight, but I don't have that manual.

[slonomo]

When a fresh engine rebuild feels like it's hard to spin, first thing I check is the connecting rod bolt torque. If you overtighten them it will make the connecting rod grab the crank journal too tightly and make it hard to turn. To test this, just back off the rod bolts just a hair and spin it over, did it improve?

The same would be true if there is a tight fit between the connecting rod and the crank. Check for burrs or irregularities there, maybe even get the mic out and measure.

Also, was the crank new as well? If not, did you polish the crank journals?

[Tfastle@aol.com]

Thanks JPon, your first answer was quite helpful. I looked everywhere but never saw that picture, just ones that had the hose sort of floating. I see now why the bends are the way there are, to go around to the front of the carb. When I tried to ascertain where it went I envisioned the black fitting it goes to facing forward and I now see it faces backwards. came out of the backwards and hence, the tube fits nicely! These are cool engines but a lot of stuff feels backward on theme to me. Carb on the front, exhaust on the rear - must be all those years riding dirt bikes! :o)

Your second answer didn't offer a lot of confidence to me. It rotated just fine with just the crank and bal. shaft installed but, because it was turning both a more heavy feel than if just the crank. I'm fairly sure the rod journal to rod bearing surfaces are good, did put the rods on before installing and they were very smooth. Also, when the pistons are around TDC or BDC it's easier to turn and very smooth.

I just went back out and turned it over again to try to paint a better picture of how it turns over. I have it completely assembled except for the clutch and timing belt cover, spark plugs out (fan on). With one hand I can grip the crank shaft where the clutch will go and turn it without straining but it does take some force, about like snugging up a faucet valve that last bit (all I can come up with). It's very smooth and a bit easier near TDC and BDC but that makes sense since the pistons aren't really moving there and no cam lobes are pushing valves down. As the pistons go up and down the sound out of the spark plug holes is not loud but audible. A tad more that the swoosh I would expect if the rings were skimming on oil. I am guessing that's normal and part of it is the lack of piston velocity, oil being splashed/shot into the cylinders and not broken in. But would like the opinion of someone that has done more of these than I (that's everyone who has done at least one).

Yes, I was hoping Trig might see this and throw in his two cents. Always helpful. Thanks for your input.

[cart around]

Here is a ring gap spec. I also found a picture a few days ago showing exactly how to identify each ring. I think it's in the same manual. I will keep looking.



Page 54 of this manual. https://www.jacobsen.com/img/manuals/27615-g01.pdf

[Tfastle@aol.com]

Thanks CartAround and Slonomo. I looked at my notes again and the end gap was .008 which, according to how I read the manual, is in specs for new bore and rings (.006-.010). No, the crank was not new ... not even close. The short story is that this engine, due to a shattered rod and broken piston, had been torn apart by someone 7-10 years ago and ultimately ended up stored outside in a box (truthfully the cart (it's an MPT) has very little time on it). The crank (and everything else) was filled with dirt and very rusty. I went down the "I'll buy a new crank" road but it didn't take long to figure out that wasn't going to happen. I took a few nights to soak the crank (and all the rusty parts) in muriatic acid and to my shock, with a lot of elbow grease, it cleaned up really nicely. I took it to an automotive engine shop and the owner did polish the journals for me and said it looked good. I also mic'd it and it was spot on. I think it's good but time will tell. Your suggestion on the torque on the rod bolts is a good one. I was careful to be right in the middle of the torque specs but you never know. Unfortunately, I have the engine buttoned up now. Not sure I want to crack it open and will have to dwell on that a bit.
I really appreciate the input and suggestions.

[trig123]

That would be a hard one for me to say . Did you check the piston you bought ? to see how it fit the cylinder compared to the other one ?

[Tfastle@aol.com]

Hey Trig, yes I did. They fit pretty much like I would have expected without rings. I have not dealt a lot with oil rings but, after noticing that the middle one held the other two out or spread, I thought it (the middle one or spring) was the wrong size or over sized so I read about them. I gather the idea of the oil ring is for the middle one, in essence a spring, is to hold or spring the other two out. There is a little detent shelf on the top and bottom of the middle one that the two others (that make up the oil ring) sit on and the middle one holds them out.

I was a bit dubious so I went to the non broken piston that came out of it, cleaned it up and got the oil ring out and it is basically the exact same with the middle one, a spring like ring, that holds the smaller rings out, larger than the bore and you have to compress it to get it on. I assume that is common but I am not an expert on 4 strokes. I now have the clutch on and, with that mass attached, it spins quite easily and very smooth. I am guessing I am being overly cautious and it's normal. Honestly, I really can't see how they could be wrong. I mean if they go in and they are STD (and not faulty) then they can't be too big.
I'm pretty much ready to drop it in and will likely do so and give it a go when I get a few minutes, hopefully this weekend but may be early next week. I'll post back her how it goes.
Again, thanks for reading this and taking the time to give input.

[trig123]

Originally Posted by Tfastle@aol.com

Hey Trig, yes I did. They fit pretty much like I would have expected without rings. I have not dealt a lot with oil rings but, after noticing that the middle one held the other two out or spread, I thought it (the middle one or spring) was the wrong size or over sized so I read about them. I gather the idea of the oil ring is for the middle one, in essence a spring, is to hold or spring the other two out. There is a little detent shelf on the top and bottom of the middle one that the two others (that make up the oil ring) sit on and the middle one holds them out.

I was a bit dubious so I went to the non broken piston that came out of it, cleaned it up and got the oil ring out and it is basically the exact same with the middle one, a spring like ring, that holds the smaller rings out, larger than the bore and you have to compress it to get it on. I assume that is common but I am not an expert on 4 strokes. I now have the clutch on and, with that mass attached, it spins quite easily and very smooth. I am guessing I am being overly cautious and it's normal. Honestly, I really can't see how they could be wrong. I mean if they go in and they are STD (and not faulty) then they can't be too big.
I'm pretty much ready to drop it in and will likely do so and give it a go when I get a few minutes, hopefully this weekend but may be early next week. I'll post back her how it goes.
Again, thanks for reading this and taking the time to give input.

You welcome. I think you pretty much got it covered. Fire it up and let us all know. Being its an MPT I assume you got an oil pressure light ?