Engine Not Starting After Port Work.

May 15, 2016
14
0
0
Auckland, New Zealand
Yo. Bet you guys have heard this one before. :/

So I've done some work on my engine & now its not starting. I cannot work it out as I know I have 1 - Fuel, 2 - Ignition & 3 - I can feel compression.

I used a dermal to port match my intake & exhaust. I cleaned up the transfers & put a bur on every edge.

I Polished the piston & gave the skirt around the intake side an opening when at piston is at tdc.

I sanded the cylinder & crankcase mating surfaces to meet flush.

I know this is quite a lot of work to do at one time which is not recommended - but I just had the engine open and the new dermal in my hand - please understand!

Oh damn & I also used jb-weld to correct the transfer angles.

The thing is when I was trying to get it started - the engine got real hot!!

I suppose there could be a leak at the cylinder head gasket which got pretty mangled- but I cannot hear it.

Or the spark is no longer sufficient to detonate the slightly increased compression?

I would even be willing to do anything to fix this - even save up for a top end rebuild, but that is so expensive in New Zealand!
:-||

!Any help will be very much appreciated!
 

Agreen

Member
Feb 10, 2013
790
9
18
Southeastern GA
Did you put the magnet rotor on backwards? It should point at the 1o'clock position with the piston at tdc.

I also assume you didn't go buck wild with the porting and do anything crazy?
 
May 15, 2016
14
0
0
Auckland, New Zealand
Yo,

Nah nothing too crazy, I did just what I was advised to do, I followed heaps of guides for the port work.

I've only taken apart the top end so the problem must lie there. She's in pieces again until I diagnose the problem.

One of my piston rings has a tiny piece broken off - like maybe 5mm off its length. Could it be that?!

Also I'm going to get a new cylinder head gasket & try to start with that - this one got bent about a bit.

Cheers.

:-||
 

Chaz

Well-Known Member
Jun 3, 2012
1,004
67
48
Vancouver, British Columbia
If your head gasket got mangled then it is likely leaking. A leak at the head gasket makes for hard starting. The broken ring is probably adding to the problem as well. Is it possible the ring got snagged on the porting mods?
 

BobbyT

Member
Mar 16, 2014
162
14
18
Santa Maria ca.
Did the ring break while you were installing the cylinder?
The broken part of the ring isn't in the engine is it? Post a picture of your corrected port. I hope a new head gasket fixes your problem.
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
6,585
381
83
Los Angeles, CA.
Post some pictures of what you did.

My best guess at this point is that you took too much off the piston skirt near the intake port. :(
 
Last edited:

2door

Moderator
Staff member
Sep 15, 2008
16,325
114
63
Littleton, Colorado
While you have things apart you'd better get rid of that JB Weld. There is a good chance that it will eventually break loose and destroy your engine. I think I know where you read about that and it is BAD advice.

Tom
 
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May 15, 2016
14
0
0
Auckland, New Zealand
Doh! I thought that transfer port correction was so clever - I tested the corrected flow with water when I was cleaning it once - you can see how the water flow will be similar to gas flow.

I'm not too sure if it was the piston skirt - as I was disassembling I noticed there was heaps still in the way. Could be though.

As for the piston ring. there is a small chance it is in the engine. I am not sure if I am good enough at engines to open up the rest & be able to put it back properly. It's got me worried though - what do you reckon?

It did dawn on me that I had a possible defective kill switch plugged in. Maybe that would be why she was heating up but just not going?

Anyway here are some pics, I really appreciate all of your help guys:


 

sbest

Member
Nov 3, 2015
343
2
18
Nova Scotia
I think you buy a new piston and you will be OK.
Too much skirt removed. Go slow, one thing at a time, have spares ready!
The gouge in your transfer shouldn't hurt anything.

I've JB Welded transfers with no problems but it depends on good prep work. Here is a Yamaha Blaster intake JB Welded:


Too much removed from your ports.
Just widen at the cylinder and port match where the manifolds fit on.
You don't need goo on the gasket surfaces. Just gasket paper will do.
Then you can do one mod and try it. Cylinder pops off and on in 10 minutes.

Steve
 

BobbyT

Member
Mar 16, 2014
162
14
18
Santa Maria ca.
If you are going to reuse your engine try and dump the the piece of ring out. Get a new cilinder and piston.
I work in a machine shop so I'm not going to say much about your dremel work.
I suggest you get another engine from VMB, if he ships to New Zeland. Do yourself a favor and ask this forum for advise before you make permanent changes to your engine.
 

Chaz

Well-Known Member
Jun 3, 2012
1,004
67
48
Vancouver, British Columbia
Joshua, looking closely at the third picture, it appears that there's a gouge in the cylinder wall. I agree with Bobby T and would replace the piston, cylinder and rings. If this is your first build I would suggest you get it up and running stock and then do mods one at a time.

A little magnet fisher should pick up the missing ring piece in the case. But the cylinder bits would need to be washed out.
 
May 15, 2016
14
0
0
Auckland, New Zealand
Yeah you guys are right - after another re-build and trying to get it started - it is F*$KED

There is a crack in the barrel, a fin just snapped off with no force and even a bit of the cyclender barrel snapped off.
I am shocked at the low level of quality of this thing - I have had a NIGHTMARE having stripped studs constantly - eventually I just swapped them all out.

A top end re-build from the only New Zealand supplier is $90 NZ so like $60 US.

It'll be a lill while before I can spend that much as I'm having to move.

When I get the new stuff I'll just go step at a time.

I just hope this doesn't kill the hobby for me. :<
 

sbest

Member
Nov 3, 2015
343
2
18
Nova Scotia
4 nuts and the head is off. 4 small nuts and the intake and exhaust are off. 5 minutes.
There is no need to do all sorts of mods at once. Without sealer the gaskets last forever.
So, read Gordon Jennings "2Stroke Tuner's Guide" and:
1) Get it running well COMPLETELY STOCK first. Learn how to make it work stock.
2) Learn what detonation sounds like, and how to read plug temperature.
3) Set up squish gap to 0.030" using 0.060" solder
4) Learn how to plug chop and read jets. Buy jets and sparkplugs to do this.
5) Buy an accurate speedo or GPS or stopwatch to measure your results.
6) Find a safe place to repeatedly do your testing. You can't improve what you can't measure.
7) Start with cheap or non-destructive stuff. Intakes, exhaust, carbs, filters, pipe length.
8) One mod at a time, little by little to see what works. Test and measure improvement.
9) Do your cylinder head first, aim for some squish area
10) As for porting, go wide at the cylinder before (if ever) you go high.
11) Match the exhaust, mismatch may be better on the intake.

Steve
 

Agreen

Member
Feb 10, 2013
790
9
18
Southeastern GA
I've been told that if you are going to trim the skirt, don't trim anything more than 60 degrees BTDC. A degree wheel of some sort (homemade is fine) will be necessary. With the intake off, mark the bottom most part on the piston at 60 deg BTDC and don't trim above that line. Make sure all sharp edges are rounded. Chamfer the port openings a little (tiny amount) to prevent ring snags.

Steve offered some sound advice. Most importantly, take your time with everything. Map out what you want to cut away with a permanent marker or machinists dye and a scribe. Don't just wing it.
 
May 15, 2016
14
0
0
Auckland, New Zealand
Yo Sweet advise guys.

I'm not a total newbie - I have had her running stock for 6 months or so & have done all the steps 'sbest' recommended up to step 9 of tuning it up from stock slowly. I just got up to porting and went too hard (leaned my lesson to the tune of $50! haha).

TBH I could do with some help with Jetting and plug reading as I feel like I might be way off.
at the moment (before I brought my dermal and had never taken the jug off) I am running an 80 main jet - My plug is telling me to go higher so now I have a set up to 100 in 5 increments to test when she is all running again.
Where should I go for some plug reading - I think I heard someone say I could just upload pics & have someone help?

I ordered a new top-end rebuild from eBay for just $50 NZD which is all good - just have to wait 10 days or so.

Once again I really appreciate all of your help fellas.
 

kelly dean

Active Member
Oct 3, 2019
139
173
43
60
kentucky
i had a similiar problem on a ported cylinder and i port matched the intake and that was the problem, it wouldnt pull fuel and when i put a stock manifold on it fired right up
 
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