Tons of compression

[Frankenstein]

Dial the crank in to check for run-out or misalignment?
Crank was true and straight as a high end arrow.

Check for fit on the bearings and install them without putting the load across the rolling elements?
Yes, fit really well actually, with the satisfying snap, I went as far as using poor man's liquid nitrogen and a bit of non-direct heat to slip them (crank on bearing) together.

Check for proper bearing side loads and clearance after assembly?
Uh... No? But it was one of those by feel things, like after torquing the case together with a torque wrench at 25lbs (what I read somewhere) the crank had no play, was centered, was smooth and turned over without any resistance. I did drill holes in it prior, so it was better balanced.

Leak test the whole assembly with pressure to test sealing?
No. However the seals and gaskets were brand new soaked with 2 stroke oil (where applicable) so they made a good seal, this is the method I use always, no problem. Gave up on rtv, messy and doesn't protect the core of the gasket, if anything it's a crutch. Heavy dose of oil keeps the water clear of the gasket, which in an engine hot enough to boil water you might want to keep steam from forming in a gasket and destroying parts of it. Water in a gasket also freezes in the winter months. Oil suffers neither bad quality. Sorry got off subject. New head gasket, installed properly as well.

Do a plug chop to assure proper mixture?
Yes, easy as pie when you have a spark plug wrench and a dozen clean sparkplugs to work with.

The engine had been running previously, no problems, only formed a small crank seal leak. Replaced it, saw my cylinder was getting a little dull, replaced and ported for a full cylinder fill from the transfers (offset the angle out slightly on one side, this results in less turbulence on the down stroke and creates more of a wall that pushes the old stuff out rather than a wet fart sorta push) , towards the back and up a bit you know blablabla. Corrected fill for third transfer (boost) port turbulence. Reed valve cleaned, checked reeds for imperfections, double checked assembly for problems. Motor ran before no problems, so not like I had a hole in the side of my crankcase.

Did not change really anything... Oh wait I did! I pulled out my old bearings, they were getting rough, I think the heat on one side was making the mag seal leak. I also replaced my crankcase gasket with real ones, it was originally a checker board box, basically identical to a cereal box. It came off the engine without hesitation except at the clutch area, but it came off in one piece regardless. Still downstairs on a glass sheet I use for gasket prep, Preserved in oil.

So tell me why after deliberate hard-assed assembly and quality control techniques I end up with a motor that either eats bearings or just runs like s**t. Meanwhile just prior the engine was a genuine half assed project but still ran better with a leak and bit up main bearings!

So the motor went to the junk box, hey somebody pulls the cylinder and Reed assembly it makes their engine run beautifully... Put that new piston and the crank into an old shell of another motor and it runs well enough to be worth a hundred bucks. Used the seals on a friend's bike and no problem. Leaves a crankcase with no found imperfections, and a clutch assembly with new pads in it. Mind boggling..

I did not change my muffler set up, I shouldn't of have to, I'm using an identical motor, with the same set up as the other, with my original muffler, and it runs fine.

I went as far as picking through the grease in the clutch spring area for signs of a leak into that, nothing. As of this time I do not have a tool for pressurizing the motor for a leak check, I do have access to a person who does. For checking that, what pressure do you think I should check to, and as far as the intake manifold goes, just tape it up? Would it be strange to put soapy water on the motor for additional leak checking during the test? Thing's covered in a brown film anyway, think a bit of dawn would be beneficial for it anyhow.

Seriously why me...

 

[Steve Best]

Ha-ha! Well Frank, you are... ...special...
I'm joking of course. I have black holes in my life too.

A rubber cork from a beer and wine making store will seal the intake, a plate and gasket the exhaust. Drill the plate for a tubeless tire Schrader valve. You can put gauge line on a nipple in the cork or drill the plate for it. Use a bicycle pump to pump up to 5-7psi (no more!) and listen for leaks. See if the gauge holds. If it doesn't, use the soapy water to find the leak.

Carefully examine the bad bearing, even cutting it in half to see the races. Where is the wear (as it were!)? This will tell you if it was installation, side load, misalignment or lube that killed the bearing and you could solve it.

 

[Deleted member 12676]

don't forget that an unbalanced crank puts huge stress on the crank bearings, increasing greatly with more RPM.
that's why no one should raise their exhaust port without first balancing the crank.
rings are either made for use on iron sleeves or plated cylinders.
If the rings these engines come with are truly made for use with plating then it's not a good idea to sleeve the cylinder with iron.

 

[gary55]

Just checking to see if my thinking is right. I read where Jag had gone over how to balance a crank by drilling 2 - 3/8" holes in crank weights to the depth of the weights width. I am guessing this is for older model engines. The engines I am getting now have two holes approx. 3/8" in each weight already in them. Does additional material still need to be removed, or have manufacturers addressed this issue? I would like to add that the GT80 engines that are being advertised as balanced cranks have identical cranks with identical holes as all the other engines I have recently ordered.

 

[Deleted member 12676]

use my balance calculator and tell me the results
http://www.dragonfly75.com/motorbike/crankbalance.html

 

[Frankenstein]

I have a zae50 rod, or at least I think I do. Has the same holes you tried to photograph in it. I noticed that my motor had a lot of additional vibration after I switched pistons, the original had the window cut out for the reed intake, I cut the entire piston skirt down and off, on my new one the piston has much more material left, I even left a small bit behind along the bottom, see pic.

Obviously I should do my new new piston the same as the old, and balance the crank a bit more. I'll do a bit more math work and play with jags calculator more.

Steve, I was thinking the same thing for a set up, only more complicated, I was going to gut (or make an effort at) a spark plug. I probably wouldn't have given up for a few days then decided I'd do it your way if I didn't know about it already.

I'm thinking this port job over carefully right now, I have a reed valve but the only opening it has is about the size of a dime, that's kinda restricted but I guess not much more than the carb intake manifold, guess the intake side on the cylinder only needs enough room for a valve end. Anything else is surplus.

I took a photo, think I found the main issue I was having, lean conditions. I bought this ported, but it appears the person who ported it went OD on it. The helicoil installed (by a third party) had its threads tapped right up to the edge of the intake.

The red arrow shows the part of the missing intake wall, the green box is a hairline crack formed in the wall, might be hard to see but it's there, also those helicoil threads are like at the bottom of the hole, way too deep, don't do it like this people.

Sideways picture, bottom is old cylinder, look at that port job, some people might say it's beautiful. Nice and big, no restriction on flow in the least. Top pic is new cylinder which is a work in progress. Look at all the space between the intake and the stud thread. It won't change much. The larger port is probably twice the size as the intake manifold by surface area. Removing that much material won't magically make the manifold or the reeds any less restrictive. It will lower crank case compression if that was the goal. Will make sealing the intake harder too.

The bottom cylinder was machined down on the intake face a bit, maybe 3mmish. That could explain the vertical over dosage of porting, because the reeds would rest a bit too low and get stuck shut. The left to right porting makes no sense.

Also they did a deep port job for the exhaust, the hole is much larger than any exhaust manifold I've seen. This just creates a larger wall for escaping gasses to fight out, and more turbulence in that area. The exhaust port inside the cylinder was a wopping 35mm wide! The outside was only 25 wide. That means the exhaust port was cone shaped, don't know if that's bad or what, still seems a bit over done. Exhaust was ported very high too, guess this was designed for speed, but I wanted low rpm power, not high rpm speeds.

The transfer ports are eh... Kinda large in my opinion, and they don't look like they would do exactly what I'd want as far as aiming the new fuel. I would have tried to compensate for the large exhaust by pushing the aim back further, a little less high, and offset the transfer angles to help them compete with the weird angle of the exhaust, it would fix the pressure difference on the sharp angle, this is what it basically looks like port wise, left side is intake.

Illustration of fuel into the cylinder, green, orange is boost.

This is sorta showing how the good fuel escapes. The low pressure (blue) sucks more than the high (red), the pressure difference is due to that sharp edge, long story short the transfer port does nothing to compensate for the lower pressure, so it looses gas by letting it out too near the exhaust.

This image would show an attempt to work the new fuel away from the exhaust port, this is commonly done with jb weld, I don't like jb weld like that but it's sometimes my only choice. Otherwise I'd just go with a cylinder with too much material and work it out like that. The pink is something like jb weld. It would fix a major loss of fuel.

I will probably leave the intake and exhaust as they are for the most part. The ports are more evenly set, I could remove more material on the hard edged side to help the gas escape a bit more evenly.

 

[Frankenstein]

I guess the moral of the long ass story is : if you want it right, do it yourself

 

[Deleted member 12676]

who was the beserko that ported it?
the widest the exhaust port should be is 70% of the cylinder bore.
yours is 74%. that wears the rings down at the exhaust side quicker.

 

[Frankenstein]

Yeah tell that to the cylinder which is probably missing as much chrome on the exhaust side as the rings were. Look at these.

Oh and jag, I have a zaf80 crank, any specs on that?

 

[Frankenstein]

More modern marvels.. This picture shows 2 pistons, both have a MNT raised lettering inside the skirt, both from the same seller, both are the same height hole, commonly called an A piston.

The left image has a raised A, the second, B

You see what I deal with?!?,..!