Removing head/cylinder on 770 Hint's I should Know!

engr146 · 10-27-2009, 05:53 PM

Besides obvious unbolting is there anything special or any hint's on removing ,To inspect whats needed for repairs .RE: Piston ordering ,Hone /bore sizeing
I know people talked about hidden bolt above starter.
I already have Pressure testing motor procedure from dank

dank · 10-27-2009, 08:48 PM

Before you unbolt the engine loosen off the PTO coupler in case you need to replace crank seals. It is very hard when it is loose on the bench.

engr146 · 10-27-2009, 09:38 PM

I thought I could do top end ,with motor in ski,unbolting intake and exaust manifold and sliding top end off pistons.just replacing pistons and gaskets.

engr146 · 10-28-2009, 04:19 PM

WSM or SBT top end kit,WSM has .25 to 1.0 mm pistons

Krispy · 10-30-2009, 10:41 AM

Quote:

Originally Posted by dank

Before you unbolt the engine loosen off the PTO coupler in case you need to replace crank seals. It is very hard when it is loose on the bench.

Haha!

Umm, yea. This is 100% true. I have a brand new vice in my shop becuase I didn't do this during my last teardown.

Krispy · 10-30-2009, 10:46 AM

Quote:

Originally Posted by engr146

WSM or SBT top end kit,WSM has .25 to 1.0 mm pistons

You first need to check what size pision is currently installed in the ski. When I first tore mine down I was suprissed to find that the engine had already been rebuild once with .25 over pistions. This meant that I could still bore the cylinders out to fit the 1mm over piston,

If your engine already has +1mm pistons installed, you will need to do one of the 3 following options,

1. Do a cylinder exchange kit from SBT
2. Buy sleeves from sbt and replace your old sleeves (the only steel in the jug assy)
3. >>Best and most expensive option: Have the cylinders Nickasil plated to build up adequate material for a bore and hone. More durable / less friction cylinder surfaces. Got quoted $150 per cylinder. Too rich for my blood.

If your engine is stock I would recommend going with the WSM kit in a diameter that is as small as possible.

dank · 10-30-2009, 11:28 AM

Tear it down first, Then you can see whats needed.

A hole in the top of the piston indicates a very lean condition, air leak, wrong spark plug, or advanced ignition.

engr146 · 10-30-2009, 04:31 PM

I Know the top end was done once before ,The previous owner did not rember what it was bored to.he said it was 92 HP instead of 90 (770) since new top end .
I just winterized and stored ski Today ,Luckily I have a heated garage to work in,and remove head and cyl.
I think dank has 770 cly.heads for sale,If needed.
When you get a small hole in piston,It does not nessarily mean I need a rebore does it,?? If no gouges ect.can't you just hone.
After all info I read,I'am contributing the hole in piston to the PTO carb.It was leaking gas severly ,when I started troubleshooting this problem and found compression 0# in PTO

dank · 11-01-2009, 10:10 PM

Correct a holed piston may not have caused a lot of cylinder damage.

Krispy · 11-02-2009, 09:53 AM

Before you remove the cylinders note that there is a hard to see/find nut that is connecting the jugs to the cases. It is located under the exhaust manafold. You must remove this nut. (All the rest that hold the cylinders on are bolts)