Any last thoughts before I buy a new one? By Doug in San Diego (Read 1,120 times)

[Doug in San Diego]

Hello All

I am thinking about getting a new engine, but before I do I thought I look at it one last time.

Here are the symptoms On my 150cc gy6 with a 59mm big bore and an A9 cam

It all began with a strange whirring coming from inside the engine. I decided to split the case and replace the crankshaft (video on YouTube)

Later the whir returned and in the end it was accompanied by a serious loss in power up hills. (that was the last day I drove it)

• I've checked the compression - 95 PSI (Low I think)
  
• When I spin the engine by hand I get air coming out of the valve cover tube into the cannister
  
• When I spin it by hand I really don't hear anything strange
  
  

I'm planning on removing the head and cylinder just to see If I can see anything.

For the longest time the whir did not cause any problems other than a noise that increased with RPMs

Just thought I'd ask for any last minute "Hail Mary" solutions before I drop close to $300 (which is a lot of money for me)

Thanks

Doug

[sprocket]

The whirring is likely a main crank bearing...but it could be the cam chain as well, it might be worn or the tensioner is no good..

The compression check is best done a hot engine...

95psi is not good... I usually rebuild at 125 psi...

You should get a puff of air from the valve cover...

[Doug in San Diego]

It's a brand new crank

Chain looks good, can't speak for the tensioner.... what should I look for

May try new rings. dunno

[cruiser]

If you can determine that the crank is OK when you do the tear down, then you might want to consider a new cylinder/piston combo for $79.99.

absolutelyscooterparts.net/catalog/150cc-cylinderpiston-complete-p-294.html

It comes with gaskets and piston rings.

[sprocket]

Did you replace the crank bearings when you did the crank?

You should check the cam chain guides, particularly the top one.. This can wear through
and make a sound... best to remove the chain tensioner and have a look down the hole at the guide...

Often the guide is broken off and the tensioner is riding on the chain...

[Doug in San Diego]

Sigh............

All right you bastages, you've dragged me back in! (every time I think I'M OUT, THE DRAG ME BACK)

Since my choices are

1) spend $300 on a new engine
2) replace the chain tensioner, guides, new gaskets, new rings (less than 50)

I'm leaning towards option #2

I really want to be that guy who says "oh it's broken? Get a new one

But Instead I'm the guy who says "I can fix it"

One last try, then it's $300 here I come

[Doug in San Diego]

I had another thought

The real question is why do I keep blowing rings?

This is probably the 3rd or 4th time I have had blown rings?

I regularly change the oil, I don't drive it too hard.

The only thing I can think of is the A12 cam I have or the long hill I have to drive up every day.

My jets are 115 and 38 - I have an open exhaust and an UNI filter.

It just does not seem right that I keep frying rings

Any thoughts

[sprocket]

It could be the rings are not in the right order OR the gaps are not staggered correctly. People say there is no difference in the two top rings , but there is...the second ring is slightly tapered and the wide tapered edge must be down. This is REALLY hard to see and the only way to tell is to use a micrometer...

In some ring sets the top rings are marked with a T or a '.' (dot)

Getting the stagger wrong or the rings in the wrong sequence on these engines and they won't last 1500 miles...

Also it is imperative that the cylinder walls be honed PROPERLY at an automotive machine shop. These hand held drill hones are a joke!

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