I think I built a GRENADE!!!

[Kevin_R_Clark]

My question pertains to balance. So here is my story. I have been hoarding 21 Picco P-5 EXR`s and parts. A while back I bought one off e-bay that was extensively modified but pretty much worn out. The case was relieved, the crank was done and the back plate modified also. Now I am not really up on doing these kind of things so I thought you got to start somewhere. The work on the parts mentioned at least looked professionally done, nice and smooth not a hack job. So I put a new RPM rod, P/L and new bearings in, set the head clearance. The first time I stated it I immediately notice it vibrated more than what I thought was ok and fuel was running out of the head. Piston hitting the head? That`s what I thought also. Took it apart and had missed a small bur on the button, and thinking about it now I think the guy kept the good one and gave me this one cause it looks like it has been thru the war. No signs of the piston hitting the head not a mark anywhere. Rechecked the clearance and put it back together. Now it runs, no leaks, but still vibrates at idle more than I think it should. Yes I skirted the piston, pretty good eyebrow but nothing like half the skirt or anything. As you know these parts are very hard to come buy so i am hesitant to throw it in an put the power to it. SOOO, is it normal for a motor with extensive crank modification and a skirted piston to vibrate at idle? I am under the impression that you really can not balance one of these motors. It has the stock flywheel also. It is an isolated mount. No I did not notice the vibration thru the boat. It is one of my habits to crab the motor by the head when it is idling to make sure it feels smooth. I have done this enough to get a pretty good idea what is acceptable and this motor is not very smooth . Reminds my of on of our fellow club members K&B Redheads that I noticed when launching that it vibrated so much it tickled to hold it. I kept telling him to balance the prop. It kept getting worse, it finally broke the rod.

 

[TimD]

Does it have a completely flat squish band or is it angled?

Also the different rod you fitted - was it considerably heavier than the original one?

When you skirted the piston - did you possibly cause some sub - piston induction?

 

[Kevin_R_Clark]

Very careful not to cause sub piston induction, has a flat squish band, and I am not sure on the rod. I have seen some pics of some highly modified cranks on this forum, lots more than this one I have. I was just wondering if grinding on the counter-weight was causing any problems. Guess I will just have to take a deep breath and find out if it is going to stay together.

 

[GTR]

Hi Kevin

Motors that vibrate badly at idle (depending on how slow you have it) often smooth out as the revs increase. Mind you sometimes they also go bang because something (rod, crankpin) is bent.

 

[TimD]

The reason I asked about the squish is because a flat squish band can make a motor feel out of balance at idle and low revs.

I guess for piece of mind more than anything checking the crank balance is worth doing.

 

[Kevin_R_Clark]

Even though I didn`t get many replies I am sure the title got some coverage so I thought I would update. I have ran the boat quite a bit now, didn`t blow up. What do ya know!! I still haven`t managed to find the set-up with this motor. I know from experience that these motors will scream. But man are these motors hard to get a reading on. They just don`t behave in a normal fashion on the bench and really only seem to like running wide open. I have 1 in a rigger that I got from Scott S and it behaves very much like the micro motor. So my next question is what do you think about taking the low speed deal out of the carb. Or an aftermarket carb. The stock motor I had in the rigger had the low speed removed and it was at least driveable. I know some of you have lots of experience with these motors , any suggestions will be tried.

 

[TimD]

Is the problem that it is hard to tune? The motor will need to sound rich down low but I doubt you would need to remove the low end needle entirely. Just back it out enough so that it is very rich at idle.

Does the idle drop off drastically when you remove the glow charger?

 

[Kevin_R_Clark]

Tim, first thanx for your help! No they do not drop off when the igniter is removed. These are the common traits i notice in both motors. Both have stock carbs. Both start right up and idle just fine. On the bench if you open the throttle both take at least 5 to 10 seconds to respond. Although I think this is somewhat a trait of these motors as the stock one was much the same only it responded a little faster but still had a definite lag. When you put them under load-in the water- they take right off. But there is no throttle ability. They are just on it. Now both of these motors are modified replacing stock set-up and motors. Also went from 50% to 65 %. I suspect a lot of my problem lies in the last statement. I need to go down on the prop sizes. I do know that the higher nitro is notoriously hard to find the needle on. So far though the needle is about the only thing that is giving me results. I can see the changes in settings on the plugs. Moving the pipe in and out does not seem to make a lot of difference. Running arround the 4in range. Think I can go a lot shorter if I can get a base set-up to work off of. The only other thing I notice is that both motors do not like to shut down. Anyhow I just have a feeling the carbs aren`t right. Thanx Kevin

 

[GTR]

Kevin

When you upped the nitro did you change the length of your pipe? you should have needed too. From memory I think it should have been a little longer. Your pipe might also not have enough volume for that % nitro. I am a believer in low speed needles but if your motor is taking that long to clean out it is probably a little too rich - that is one of the points of a low speed needle so that the mixture doesn't have to be so fat at the bottom end but can still be fat at the top. When idling does your motor just sit there idling or do you need to blip it to keep it running? You could try an airbleed to lean out the idle mixture a little if you want to keep the mixture really rich. Don't remember seeing it or not but what is the throat on these carbs?

GT

 

[TimD]

OK, from your last post I would say there is very little chance removing the low end will fix it. Like GTR I too like a low end needle but you do have to know how to set them up.

The hesitation you are getting when you open the throttle should be no more than about a second or two when the low end needle is close to right, so start winding it in until the hesitation is reduced. If it keeps screaming after you let off the throttle you have gone too far. You want the low end to be on the rich side.

Before you go and put the boat in the water and give it throttle, Richen up the main needle by about a turn, and fit a NEW plug.

Fire it up - check the idle hesitation again - then give it a run on the water.

Do you know how to read you mixture on the glowplug? If so just lean down the main needle until the plug is OK and the motor cleans out OK on the water.

It might help also if you list the boat type, pipe and length and the prop info so we can see if something is way off!

Hope this helps.

Tim.