Engine locks up on bottom dead center

Schrockie · Oct 23, 2015

Thanks Tom for getting rid of the double post.

As I said earlier, I have never messed with the crank on any engine before and not sure how to disassemble it, but I do want to replace both main and the rod bearings, just need to know if I need some kind of gear puller or what. Any videos or links to videos would help. I don't want to replace the just seals, put it back together again and have it lock up again. Do it right while I have it apart now.

On another note, fired up the new Flying Horse engine I got from bikeberry.com and for break-in they recommended 2 tanks @ 16:1 synthetic(using Maxima ScooterPro2T). After that they said use a 20:1 ratio for normal driving, isn't that a little rich? With the old engine I was using "Opti-2" 1.8oz individual packets per 1gal.(ratio 70:1), but I've heard a lot of people talk about using 30-35:1 ratio, Any advice?

Troy

Schrockie · Oct 23, 2015

I just read the thread "Gas to oil ratio?" with the link http://motorbicycleracing.com/2-stroke-oils.html and it answered/cleared up most of those questions. Now I just need to learn more about re-jetting and fuel/air mixture, basically anything on how to tweak my carb.

YesImLDS · Oct 24, 2015

2door said:
The dark magneto coil doesn't concern me and there is no evidence of oil in the magneto area so I don't see a seal problem. But, since you've got it down this far I'd suggest replacing both seals while you have it apart. Cheap insurance, for sure.

I deleted that duplicate post for you.

Tom

I agree on the dark magneto I pulled one like that out of a ebay engine and it ran perfectly that way. I replaced it anyways when I combined a couple engines due to a striped head stud just because why not have prettier parts? Anyways like Tom said no worries.

Davezilla · Oct 24, 2015

I also agree... everything looks ok in there... if you want to replace the main bearings, be sure to get good ones like skf or Timken and you can get the sealed ones, just remove the inner seal and leave the outer seal in place, this will allow the oil to get into the bearings but give you and extra line of defense in case a crank seal goes out, just be sure to put a light coat of grease on the seal lip before you install, and put something between the flywheels to prevent the crank from "bending" when installing the case halves back together.. a small wood block is easy to make, insert, and remove before and after assembly.
There are several YouTube vids that show the assembly process and what precautions to take to keep the crank straight during assembly as the flywheels can rock on the crank pin if too much force is applied and there's nothing set between the flywheels to support them. Fred has some really good assembly videos explaining this. Also check your clutch shaft bearings before going back up with the engine as these can take some abuse, the one I took apart had both clutch bearings shot as well as one crank bearing.

Schrockie · Nov 3, 2015

I was reading some threads the other day and was interested in buying a complete crank that was already balanced. I can't remember the thread and didn't jot down the name's of the vendors who sold these. Can anyone help me out with my rebuild?

Schrockie · Jan 16, 2016

Actually I now have time to do the rebuild and I just now am noticing these small gouges on the magneto side of the crank. These are probably from the retaining clip that failed.

crassius · Jan 16, 2016

not sure if it's my eyes or that pic, but I can't tell what part it is - if that is the mag side crank cheek, then I'd be looking for a head stud pushed down too far or something just lying on bottom of case

Schrockie · Jan 17, 2016

Correct, the silver part is the crank and the brown is the rod. I had the case split and their were no other obstructions. Back on the bike and the engine is running smoothly until I engage the clutch. Then something starts to grind, not constantly, only during part of the revolution like something might be off center. Took the clutch cover and chain/clutch arm cover off and nothing suspect in their. Any ideas?

crassius · Jan 17, 2016

look for crank float right/left - the angled teeth on that bevel gear can drive it pretty hard sideways

if a stud is too far down, the bump will be at top of case

Schrockie · Feb 6, 2016

my engine runs fine, then all the sudden shakes and rattle. have normal rpms, all the sudden it revs so high, sounds like its on the vergee of exploding.throttle cable is between my leg and its not sticking. like i said, one mooment, nice and smooth, then the next its screaming at me?
screw for carb only has 2 turns left. its not that and cable is between my legs, not sticking??????????????????????????????????

crassius · Feb 6, 2016

sounds like carb is too rich & suddenly breaking into 2-stroking rather than 4-stroking - try dropping needle down a notch or two & see what happens

also could be caused by air leak at carb or loose motor mounts

try the carb first 'cause it's easy to put it back if that isn't it

Schrockie · Feb 13, 2016

did all you said and some things on my own, this is the nt carb. put the stock carb back on and it runs. still alot of vibs, mounts are tight and true. have rpm guage, speedo took a dump, @ 3500rpm(25-28mph) used to run smooth but now the vibes are a nuisance. @ full throttle it used to go up to 4300rpm(36-38mph). drove it around for about 1/2hr max rpm was 3800 by the time i got back home max rpm was 3400 and the head was reading 350f. which is high to my usual 300-325. any suggestions?

Thanks,
Troy

crassius · Feb 13, 2016

could be a slight miss in ignition or a bit of intermittent 4-stroking

Schrockie · Feb 13, 2016

Miss in the ignition? How, What? Theres a magneto and coil/cdi, how do i check these, i do own a multimeter/voltmeter. I really don't think I have any elec issues. One thing I did notice between the stock and upgrade carbs was: Stock carb fuel/air adjustment screw was almost all the way out, while my NT carb screw was all the way in. unscrewed the NT 2 times counter and engine would bog? Could there be anything internal, jet, float? About those two, if the float is screwed, I would have no fuel or too much and it would spill out, jets I have no knowledge at all.

I really appreciate you responding to this old post, I'm not a newbie to how these engines work. It's just everyone gets stumped now and then. once again Thank You

Troy

crassius · Feb 13, 2016

a slight miss means all ignition parts are working but a spark gets lost every so often - this is usually fuel or oil soot gets on wires making insulation break down or a plug that is about to fail

standard NY has no mix screw, just the idle speed screw - often when the idle screw needs to be almost all the way in, one needs to change the mix by dropping the needle down a notch or two lower into the slide

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