Holey Piston Batman!

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chuck12563

chuck12563

New Member
Jun 8, 2011
12
0
0
Patterson, NY
OK, should this happen to a new motor. Less than 2 hours of run-time and 39 miles traveled. Break-in oil mix 24:1. Brand new Grubee 66/80CC Skyhawk Angle Fire head. CNS V2 Carb. I got it from Piston Bikes.

See the photos.

Did I do something wrong or was this motor defective.

And prior to this after only 1 hour of run time and 19 miles the head gasket blew. Looked like it was put on bent at the factory.

At a minimum I need a new piston, cylinder, head/cylinder gaskets. But is this worth fixing as there appears to be quite a bit of piston pieces in the crankcase. ?

If I decide to fix this, will I have to do a complete tear-down? I know, I probably should if it want it to last.
:-||

Chuck
 

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Al.Fisherman

Al.Fisherman

New Member
Sep 9, 2009
1,966
5
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Calera, Alabama
I myself would fix it.. Chinese HT breakdown pictures by Ron-Becker - Photobucket for help.

Here are some inexpensive mods that you can do if rebuilding it.
These are the things that I do, I see that others such as the seals (which I've never had one go bad) mentioned. All these mods or replacements are most likely less then $50.00. Choose what works for you, ignore the rest, but here you have them.

1. Unpack engine
2. Check for any missing parts
3. Remove head
4. Mill head (flat glass and 230 (or finer) grit sand paper. Rub gasket surface to insure it is flat. Check the cylinder also.
5. Tap cylinder stud holes to insure they are taped to the bottom.
6. Discard all studs and nuts.
7. Replace studs with Metric 8.8 (US Grade 5) Replace nuts with locking nuts. 8mm studs are either 1.0 or 1.25 thread, 6mm studs are 1.0 thread. 8mmX1.0 is not common, but I have 1 engine with them.
8. Replace spark plug with a NGK or the like.

9. Replace spark plug wire and boot (check with lawnmower supply) or rob from old lawnmower. Use wire core lead.
10. Mount the engine properly, no gaps between the bike tubes and engine mounts.
Engine Mounting pictures by Ron-Becker - Photobucket
11. Torque 8mm to 150 to 200 INCH POUNDS
12. Torque 6mm to 60-70 INCH POUNDS
13. I install cylinder studs with lock tite, and let set overnight
14. I coat the head gasket with Copper Kote
15. May need to bend exhaust pipe for crank or frame clearance. Recommend using heat.
16. Remove or cap magneto white wire off.
17. Re solder blue wire on magneto.
18. Make sure all wires have a good connection and use tape or better yet heat shrink.
19. Hook up kill wires AFTER you get engine running.
20. Try not to drill holes in the bike frame.
21. Do away with the clutch cable routing; there are a number of options.
Homemade Mods pictures by Ron-Becker - Photobucket
If you want to make yourself, PM me and I’ll give you a material list.
22. On my kit the rag joint had gauge (Metric) 8.8 bolts, If not replace them. I replaced the nuts with lock nuts.
23. I sealed the wires coming from the magneto out of the engine with RTV.
24. Place a “O” ring in the carburetor throat.
25. Some say replace the axle with a better one. Never had a axle bend on me.
26. For coaster brakes…Some say trim the cap, but I don't like it. ‪Bearing cap mod‬‏ - YouTube or a file of sorts can be used.
 
F

flatblack

New Member
May 22, 2011
374
1
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Fairfax, VA
Screw it. Buy a new motor. You've got the rest of the kit. Sure, it's always good to tear down and know you're motor inside and out, but for $100, you can be up and REALLY enjoying the thing by riding it.

Sorry that happened to you. I know how it is to get the bike complete and running well, then having some BS happen to you. Nothing worse to see it sitting in the garage idle...without idling. Ditch the CNS carb on the next motor. Make sure you check the head bolts and head. All should be tight and true. ****, replace the crap head studs with a kit offered by Pirates from the get go. You'll know they're gonna last and take the prop torque amount.
 
chuck12563

chuck12563

New Member
Jun 8, 2011
12
0
0
Patterson, NY
Thanks for the advise Ron, I have a new engine coming (NOT from Piston Bikes) and will follow your recommendations.

I finally got in touch with Piston Bike (the guys I got my engine from) and was told that I burnt up the engine because I didn't use a 16:1 gas/oil mix, I used a 24:1 mix.

Any thoughts?
 
GearNut

GearNut

Active Member
Aug 19, 2009
5,104
11
38
San Diego, Kaliforgnia
Thoughts?
They are weaseling themselves out of a warranty claim.
16:1 is a horrible ratio to break in a new engine.
Also, lack of oil did not cause that damage.

Porous casting (air bubbles in the molten metal) of the piston perhaps?

To be honest, it looks like someone smacked the top of the piston with a punch and hammer. Sprinkled some metal shavings into the cylinder port and on top of the crankshaft.
Never in my 29 years of wrenching on engines of all sizes and causes of failure have I ever seen that kind of damage.
Something is fishy with this scenario...........
 
retromike3

retromike3

New Member
Jan 9, 2009
148
0
0
Beaverton OR
I had a hard time getting my bike to run at 16 to 1. I think you just got a lemon. I got mine up and running on a 24 to one rate and have had no problem(so far) My CDI was defective and the carb was funky, but the engine was sound.

I think you will have to write this one off, so just take it apart and store your parts in separate containers and bags and make sure you label your parts.

you now have a set of repair parts for your new engine. One of the neat thing about this hobby it if all else fails you not out a lot. My Boy Go Fast ate a pin clip and froze up, so I bought a replacement engine from zoom cycles out of Canada and it ran like a top.

So you might just chock this one up for experience and move on. I really don't know if it's worth the effort to try to get your money back, if they want to stiff you.


mike
 
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chuck12563

chuck12563

New Member
Jun 8, 2011
12
0
0
Patterson, NY
I'm not going to fight over the money as it is just a waste of time. If they had offered to send me replacement parts (I was willing to pay for shipping) then they would have had a customer for life. But instead they have an ex-customer for life.

So I have a new motor coming from BGF and can't wait to compare it to my dead brand-name Grubee. If this new motor works out then BGF has a new customer for life.

It helps to have something to compare to so that you can then make judgements as to whether something is good or bad.

Chuck
 
chuck12563

chuck12563

New Member
Jun 8, 2011
12
0
0
Patterson, NY
My new engine arrived yesterday, a 66/80cc from BGF, and I followed a lot of Ron’s recommendations. Here’s a list of them:

Milled head--it had left over metal material stuck to the gasket area.
Tapped cylinder stud holes--they didn’t go all the way.
Replaced all nuts.
NGK spark plug.
Torqued head nuts to 12.5 foot/pounds
Coated the head gasket with Copper Kote
Capped magneto white wire off.
Kill wires not connected until engine is running.
Clutch cable routing using the roller set up.
Switched to a #41 chain (from Tractor Supply)
Added a dual pull brake handle
Added a rear caliper brake (already had a front one)

I drained the old gas/oil mix and I’m switching to STIHL HP Ultra 2-Cycle Engine Oil (full synthetic) It is recommended to use a 50:1 mix for break-in (of their equipment), but I’ll going to error on the side of caution and use a 25:1 mix.

I’ve run out of daylight for today and I’ll fire it up tomorrow after work.

I did notice some differences between my Grubee and the BGF engines--both 66/80cc.
Grubee 6mm head studs, BGF 8mm head studs.
Grubee cylinder casting was better than BGF (bent fins)
The BGF engine had better quality screws, nuts and bolts than Grubee, but they still had to be replaced.

As an aside, BGF claims that his top end parts will fit my grubee. He has a good deal, piston-cylinder & rings for $25. If I decide to rebuild it, I’ll chance using BGF parts and while I’m at it I’ll drill and tap the case for 8mm studs.

The only thing with BGF was that the engine I bought was listed as a slant head, but I got a straight head. This is really OK as now I will have something to compare to.

I also ordered an NT carb from BGF, but I’m sticking with my CNS-V2 for now. When I took the CNS carb off the Grubee I found that the intake manifold was cracked. Could this have created an over lean condition and led to the piston destruction?

I ordered one other item and that was a long handle clutch lever. I thought that it would be better than the clutch lever that came with my Grubee kit, but it wasn’t, it did not have enough pull of the cable.

I wanted to replace my kit Clutch lever because of the way the lock button worked. Clutch cable adjusted so all slack is gone (arm at 6 o’clock). Disengage clutch, lever is pulled to 4 o’clock position. Push in lock button and the lock does not kick in until the arm has moved backward to about 5 o’clock (not enough to have the clutch fully disengaged).

I had tried a brake lever and it did lock at maximum pull, but it only had enough pull to get the clutch arm to the 5 o’clock position (just like the long handle lever from BGF).

So am I doing something wrong and should it take a lot less pull to disengage the clutch?

Thanks,
Chuck
 
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