Low Compression in Cylinder 1

[rdbul]

I have an 89' Max with 22,000 miles on it, Pods, Stage 7, and Cobra exhaust but otherwise stock. The last time I rode it developed a exhaust thump, the regularity of which had me thinking it was a single cylinder issue. Did shotgun, no improvement. Pulled plugs, verified spark, and compression tested. With WOT three cylinders are very close @ 165- 170. Cylinder 1 (?, front left) is at 140. I have only had the machine about 2000 miles and assume the valves have not been adjusted, ever, which was on my to do list. The plug for this cylinder appeared a little lean (brown with white). Seems unlikely to be a ring issue as there is no oil on the plug and the low mileage on the motor.

Any input is appreciated regarding this issue before I start tearing into it. Thanks Guys.

 

[sdt354]

I'd adjust the valves to start,the exhaust may be too tight by now. While the carbs are off take a peak down the maniflods and check for heavey carbon buildup.
Steve-o

 

[Rusty McNeil]

i'd adjust the valves to start,the exhaust may be too tight by now. While the carbs are off take a peak down the maniflods and check for heavey carbon buildup.
Steve-o

+1,

 

[rdbul]

I've been running 89 octane with startron treatment enzyme. Do you guys think using 93 actually contributes to carbon build up?

 

[sdt354]

I've been running 89 octane with startron treatment enzyme. Do you guys think using 93 actually contributes to carbon build up?

Carbon build up is going to happen no matter what gas is used. But 93 octane? If it made me run better I wouldn't care. I don't see it being that big a difference. But that's just my opinion.
Steve-o

 

[Rusty McNeil]

Just my opinion but as stated before carbon buildup is going to happen no matter what with a carbureted engine, its just a matter of degree.



Mostly attributable to rich condition as opposed to what type of fuel your using.

Modern fuel injection you don't see it as much because the things are mapped to be as lean as possible under whatever the conditions are.

 

[rdbul]

I have tried the dribble water in the carb trick on the suspect cylinder. Also tried it with ATF. No improvement. Tore it down and here is what I measured. The highlighted intake value is suspicious.

Please check my logic: if the valve seat had carbon stuck in it, the now wore in seat which should measure around .12mm may return a measurement that is greater than it should be - like this one.

Trying to think my way into this as pulling the head doesn't sound like a lot of fun, but if thats what it takes, thats what it takes.

Thanks guys.

 

[rdbul]

I have the motor out of the frame and the heads removed. My plan is to replace 25 year old valve seals, inspect valves/ seats, lap valves, paint and reassemble. Hopefully find something suspect on the low compression cylinder valves. Valve measurements are in the picture in my last post.

The motor has 22K miles and I had low comp in one cylinder, 140 vs 165-170 on others. Would I be foolish at this point to not lightly hone and re-ring it?

What else might I want to consider doing while its apart? (besides a bore kit) I really don't want to have to go into it this deep again for a long time.

Your experienced feedback is greatly appreciated.

 

[[email protected]]

1260 bore kit. Valve job. Valve seals. Check rod and crank bearings. HD oil pump upgrade. Blast clutch steels. New frictions. Check slave, replace if you have any signs of issues. Check starter clutch. Water pump bearing, mechanical seal and gaskets. Etc,etc,etc....

Or put it together and cross your fingers

 

[sdt354]

I have the motor out of the frame and the heads removed. My plan is to replace 25 year old valve seals, inspect valves/ seats, lap valves, paint and reassemble. Hopefully find something suspect on the low compression cylinder valves. Valve measurements are in the picture in my last post.

The motor has 22K miles and I had low comp in one cylinder, 140 vs 165-170 on others. Would I be foolish at this point to not lightly hone and re-ring it?

What else might I want to consider doing while its apart? (besides a bore kit) I really don't want to have to go into it this deep again for a long time.

Your experienced feedback is greatly appreciated.

Your budget is your only limitation. 22k is a very unused vmax engine. At this point I'd check the rings for sticking. Then either put them back in (no honing unless complete disassembly)or go the build route. +1 on the 1260. It would be a lot of fun.

 

[rdbul]

I'm planning to use aircraft stripper to clean the paint off the outside of the head. Do I need to be concerned accidentally affecting the black paint/coating inside of the head?

 

[one2dmax]

I would take the head to a local plastic or soda blasting company. It will be much easier to prep for paint and should be relatively inexpensive.