Any GX670 experts ?

[Sideleaner]

Hi guys, need your help on the stump grinder engine.

The Honda GX670 produces white smoke, I already checked the following :

 

- cleaned the carb, nothing wrong with it.

- checked the vacuum fuel pump, let the engine run with the gas tank above the engine, avoiding the fuel pump. This is to enliminate if the pump would suck oil from the crankcase. The cranckcase breather is clean and free.

- ignition, both sparks are firing.

 

Strangely one cylinder stays cold while the other one is hot.

I guess the cylinder head gasket is blown ??

How do you remove an OVH head. Just loosen the 4 bolt and take it of, or do you have to remove the valves, springs, push rods, tumblers etc ?

I am going for a pressure tester tomorrow, and measure the difference between the 2 cylinders. Maybe this will confirm the gasket issue.

 

Any ideas ?

 

Pascal

[tommer9]

Does it sound rough and run badly?

i mean theres no chance the rings are gone in one cylinder?

What does the smoke smell like? And is it white or pale blue?

[windfall]

If you are only on one cylinder i think something more drastic has happened than the head gasket. White smoke is probably going to mean oil is getting in the bore...

 

Your going to have to strip it down i recon, OHV heads come off easily, try to note which rod goes in where. I put them in card board.

[Sideleaner]

Does it sound rough and run badly?

i mean theres no chance the rings are gone in one cylinder?

What does the smoke smell like? And is it white or pale blue?

 

It runs fine at low and moderate rpm, but when I open the throttle, there is a BIG cloud of white or lightblue smoke (can,t really tell with all that snow ) It smells like burned oil.

The engines is at 450 hours.

 

Pascal

[Sideleaner]

If you are only on one cylinder i think something more drastic has happened than the head gasket. White smoke is probably going to mean oil is getting in the bore...

 

Your going to have to strip it down i recon, OHV heads come off easily, try to note which rod goes in where. I put them in card board.

 

So I can leave the valves in the head ? Just remove that bolts of the cylinderhead and lift it off ?

 

Thx your replying

 

Pascal

[TimberCutterDartmoor]

Ha! the infernal GX670; I had a very steep learning curve with one of these on my chipper. Is yours the 20 or 24 hp version?

 

I will attempt to attach a link to a brilliant video about this engine...

 

This engine is FAMOUS for running on one cylinder!

 

Note - burning oil produces blue smoke not white. White is either steam which is unlilely on an air cooled motor (!) or quenched combustion. These buggers are designed to run lean for CARB approval so see what happens when you apply a little choke during the problem running.

 

I would start with a tear-down of the air box and carburretor, the latter has a breather which stupidly allows the emulsion tube to breathe in crap - you need to mod this as per the vid.

 

This engine is also fussy on a) fuel quality and don't use high octane, b) check for water in fuel c) spark plug gap and correct type and tightness...

 

Link to video here:

 

http://arbtalk.co.uk/forum/large-equipment/13532-honda-24hp-v-twin-problem.html

Edited December 18, 2010 by TimberCutterDartmoor

[windfall]

Yeah the valves will all stay put.. unless they are broken or the collet is broken! ;-) either way you will have found your problem, parts are dirt cheap on line. You may have to wiggle the head to get the con rods to drop out or pull them out with the head. Above all dont be scared the GX series motors are really easy to pull apart and fix.

 

Sounds to me like a valve spring or locating collet may have gone and is allowing oil from the head into the bore. It will also mean there is no compression on that side so if you have a compression tester it will show this.

[windfall]

Note - burning oil produces blue smoke not white. White is either steam which is unlilely on an air cooled motor (!) or quenched combustion.

 

This is not always true, i have had so much white smoke out of one of my GX motors it was like a smoke machine used on a battle ship. Perfect white smoke.. That was engine oil in the bore from tipping the engine on its side.

[TimberCutterDartmoor]

Note - burning oil produces blue smoke not white. White is either steam which is unlilely on an air cooled motor (!) or quenched combustion.

 

This is not always true, i have had so much white smoke out of one of my GX motors it was like a smoke machine used on a battle ship. Perfect white smoke.. That was engine oil in the bore from tipping the engine on its side.

 

Then it's a combination of the two; oil control rings work at any position but the slop in the cylinder head is what gets through from the top which in turn swamps the mixture which burns cold = white smoke

 

Likewise, crankcase oil contamination with fuel = the same.

 

Crankcase breather - check.

Edited December 18, 2010 by TimberCutterDartmoor

[Sideleaner]

Well, I had a look at the other threat, and located the breather hole on which a rubber hose was fitted. Blew out the thing but I am suspicious about it being clogged. So I took it to the Stihl workshop where good old Joh(a)n will put it in the ultrasonic cleaner. It needs a good cleaning after all with 450 hours on the meter.

I borrowed Johan's compression tester, and to my surprise the defective cylinder has more compression than the good one

I have about 120 psi/sqinch on the bad one and 100 psi on the good one.

So there is not a problem with valves, gaskets etc.

Will now check the valve clearance.

I will have the carb back next tuesday, I hope the prob is solved.

 

Pascal