Topic: 1966 FD 20 troubles – Antique Outboard Motor Club,Inc

This topic has 26 replies, 6 voices, and was last updated 9 years, 6 months ago by fleetwin.

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February 12, 2016 at 11:24 pm #3627
wiscoboater
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Hi guys,
Working on a 66 FD 20. The motor looks pristine, looks like it has very little hours on it. It runs, poorly. It will start, has great spark, carbs most likely need rebuilding as it wont stay running after being started. The big issue I have with it is compression. I have 116 on the top cylinder, 60 on the bottom. Soaked the lower cylinder with PB Blaster for a week thinking perhaps a stuck ring. No change. I pulled the head today to look over the cylinders and head gasket. (see pictures). All pictures show the lower cylinder to the left. The lower cylinder on the head is very clean, hardly any carbon compared to the upper. water intrusion? I did not see any obvious leak in the head gasket, but it looks a bit weird on the lower cylinder. Piston is also much cleaner then the upper piston. The cylinder walls are beautiful, no scratches or glaze. In fact, looking closely at the lower cylinder I can still see slight cross hatching. What are your opinions looking at the pictures. Put in new head gasket and try again or is there some cause of the low compression I am missing. Any advise welcome.

Thanks, Wannabe
February 12, 2016 at 11:54 pm #31845
chris-p
Participant
Looks like the head gasket failed around the lower cylinder ring? Or is it my eyes.

I would check the bore while I had it open, ensure the rings are free and not stuck.

Then check the head to be true, straighten by sanding in figure 8s on emory on plate glass.

Install new head gasket, and torque to spec.

Then re test.
February 12, 2016 at 11:57 pm #31846
wiscoboater
Participant
So in that case would I be losing the compression into the water jacket?
February 13, 2016 at 12:09 am #31848
frankr
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US MEMBER PAY BY CHECK
I’d say the head gasket is leaking a bit, but not enough to cause such a drastic loss of compression. You need to look further. Pull the intake bypass covers and exhaust cover for a look inside. And go from there, according to what you find. Once you find it, it will be obvious.

BTW, that lower cylinder is washed clean, either by raw, unburning fuel going through or yes maybe water. Water can be coming from the exhaust cover—which you are going to pull, right?
February 13, 2016 at 12:23 am #31852
wiscoboater
Participant
Frank, Yoda,
I will pull them all. This is a learning opportunity for me. You have been wrenching Johnsons longer then I have been alive. Your knowledge and that of Chris is what I am hoping I can learn from here. I will investigate further tomorrow and let you guys know what I find. One question, in the cylinder head pics I can see what appears to be brass around the cylinder head as a seal? Is that in the gasket?
February 13, 2016 at 12:55 am #31853
chris-p
Participant
Yes, built in the head gasket. You can see, even on the combustion side, where the bottom cylinder seems to be corroding more than the top cylinder around the cylinder bore. In my humble opinion, you have water intrusion there.

As Frank stated, there is likely more going on, but that is at least one of the issues of the poor running that will need to be rectified. Luckily, that is an easy fix, per se. It looks to me like the gasket is deteriorated around the bottom cylinder, but check the head to be straight as well. I sand and straighten every one I take off, just to be sure.

Hopefully your exhaust screws come out with ease! Removing the exhaust cover, and bypass covers, will allow you to check the rings for bounce, and for damage to the sidewall of the piston.

If you happen to have a new piston ring, you can drop it in the bore, and check the end gap. If the end gap is in speck, the bore is likely good. Red neck way to check a bore I know, but not all guys have bore gauges.
February 13, 2016 at 6:28 am #31873
Mumbles
Participant
I think the low compression might be causing the bottom cylinder to be cleaner/wetter than the top cylinder. The air/fuel charge can’t burn properly with that low compression and goes right thru the motor half burned leaving the oil behind. Wet looking carbon deposits are more common on the 24:1 and 16:1 motors but these 50:1 motors usually leave hard and dry deposits on the pistons and head. Water getting in will usually clean the plug white and leave small rust deposits on it but these plugs look well used and are probably ready to be replaced.

A small amount of water may be getting in thru the lower crank seal as you can see how the lower piston is clean where the intake ports line up. Water getting in here will wash any oil off the cylinder wall causing scoring and galling which causes, you guessed it, low compression. The head gasket may be weeping but if it was blown, exhaust gases would get into the cooling system causing the motor to overheat so it’s probably a mechanical issue causing the low compression.

Ahhh, mid sixties FD’s, great motors!

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February 13, 2016 at 2:25 pm #31879
wiscoboater
Participant
Mumbles, are you running J 4 or J 6 plugs in your FD’s?
February 13, 2016 at 3:15 pm #31883
fleetwin
Participant
US Member
yeah, I’m with Mumbles and Frank. Head gasket looks "OK", surely not bad enough for such a low compression reading. Try pulling the intake cover first, then go to the exhaust cover, just trying to avoid breaking the exhaust cover screws if possible.
February 13, 2016 at 4:38 pm #31888
wiscoboater
Participant
Well, I pulled the exhaust cover this morning. Screws came out like it was a brand new motor. Not one gave a fight. I found the lower piston has a large gouge in it starting at the top ring and going through the other two rings and down the skirt. This has the rings locked up and the lower half of the cylinder has a corresponding gouge from the top of the port down. I guess this power head is done. My shop camera does not take good close ups, but if you look at the 3rd port from the right you can see the damage. I have another power head from a 62 that’s good so I guess i’ll swap it and make it a good motor again. It’s really a shame as this is about the cleanest original FD I have ever come across.
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