520 Continental rebuild

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rowdy1
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520 Continental rebuild

Postby rowdy1 » Wed Oct 03, 2018 9:15 pm

I have my 520 Continental scattered across a sheet of plywood. I have been posting on and off for over 3 years about an overheating problem. I have rebuilt the carb, resealed the intakes, replaced the rubber boots and clamps, installed pacemaker ign, changed the oil cooler 3 times. Nothing has fixed the problem. Yes I run avgas, no I don't run the hell out of it. Well it finally got to hot and started to make metal. So I got pissed and tore it down. JUST IN TIME! The rod bearings are starting to show copper and the mains are trashed. Several reliable engine builders have suggested the cam timing might be off.

Bottom Line: If I am going to rebuild it Im going big. I want any and all ideas on how to make it better. I have heard of different cams, adjustable push rods, roller rockers, 540 rods. Tell me what you know, I will Frankenstein some crap together as long as you are sure it will work!

P.S. I have a fresh set of 520 jugs and pistons, so no GITSOs.

Thank You

Gary S
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Re: 520 Continental rebuild

Postby Gary S » Thu Oct 04, 2018 6:42 am

If you don't run the hell out of it why Frankensteine it? 520 makes good power and its going to be a lot better than it was. What pistons you going use with fresh cylinders? Your going to spend a lot of money thats not needed. Hard to improve continental cam.

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John Fenner
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Re: 520 Continental rebuild

Postby John Fenner » Thu Oct 04, 2018 10:54 am

Well 2 other things can cause overheating, take the vernatherm and test its operation the same way you would a car thermostat, if it is not extending out to bypass oil through cooler, that is a problem.

Next, check the condition of the ring lands in the pistons, if they are worn, it will cause combustion to superheat the oil, sometimes with no notable blowby or oil usage.

If it has the 8.6:1 pistons I would suggest running mag timing at 22° max.
When you go back to together I'd suggest a hard runup for break in till hot, shut it down with minimal idle time and let it cool all the way down, check plug color, if not tan on insulator, it needs more fuel.
I never finish anyth,,,.

rowdy1
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Re: 520 Continental rebuild

Postby rowdy1 » Thu Oct 04, 2018 4:30 pm

I have a set of Superior cylinders that are take offs w/ 450 hrs. They had an AD for injector bosses or something. They are complete including pistons, pins, rocker arms, everything. I spoke to a builder this morning that said the same thing about the cam. He suggested a set of 10-1 ross pistons and build the rest back to stock. He also suggested NO Lycoming rods!

This was a fresh rebuild, and I ran mineral oil in it for 50 hrs. It never made it to 70 hrs. There is no vernatherm in the motor, the passage was threaded and a pipe plug installed. This was a low compression motor, and I ran it with mags set to 22* and with Pacemaker ign. and there was no difference in the oil temp. It went from start up to 230* in 15 minutes of normal riding. I did inspect all of the cylinders after tear down and none of them show anything obvious.

jsapp
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Re: 520 Continental rebuild

Postby jsapp » Fri Oct 05, 2018 9:39 am

Did you check temperature at the oil cooler from side to side to verify you have flow? there should be a temperature difference between the inlet and outlet. Does the gauge read zero degrees when cold? I have seen inaccurate gauges more then once...

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John Fenner
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Re: 520 Continental rebuild

Postby John Fenner » Fri Oct 05, 2018 12:58 pm

There lies the problem, no vernatherm, no oil forced through cooler, reinstall a vernatherm, may have to reverse engineer the passage so it seats correctly.
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StanleyAirboats
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Re: 520 Continental rebuild

Postby StanleyAirboats » Fri Oct 05, 2018 4:11 pm

if it is tapped and plugged correctly it forces the oil through the cooler it has no choice but go through the cooler.

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Re: 520 Continental rebuild

Postby StanleyAirboats » Fri Oct 05, 2018 4:25 pm

what cam is in it . what was the valve lash set at. there is a number of things that could be going on could have the wrong bearings in it to. what is the oil presser at start up and when it gets to 230.

rowdy1
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Re: 520 Continental rebuild

Postby rowdy1 » Fri Oct 05, 2018 7:14 pm

It is supposed to have a 661 cam. It and the lifters show absolutely no wear. Honestly there didn't seam to be much lash at all before dismantling. There is nothing to adjust so im not sure how you would change that. The motor was built by a guy that at one time built a good motor in north FL, I wont use is name. I was told by two other builders that this person would advance the cam to get a little more power. I marked the cam and crank where it came out but I am not sure how to tell what I have. All I know is its cooling off and I want to go fishing. I need my junk running! For the first time in my life I have the money to fix a project correctly, just not sure where to start.

Thank you to all who are trying to help.

rowdy1
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Re: 520 Continental rebuild

Postby rowdy1 » Fri Oct 05, 2018 7:28 pm

Oil pressure was over 80 cold, even with the main bearings trashed, at 230* it was over 50. I belive I am responsible for the bearing problem. I ran it way to hot and lost oil pressure. It did come back after cooling but Im sure the damage was already done.

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Slidin Gator
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Re: 520 Continental rebuild

Postby Slidin Gator » Fri Oct 05, 2018 7:53 pm

rowdy1,
Oil temperature is just that, oil temp. It does not really have much to do with cylinder temp unless there is a piston and/or ring issue blowing hot combustion gas into the crankcase. Valve stem seals are a minor possibility. You have noted that the pistons, rings and cylinders are all good. Unless you note indications otherwise, assume for the moment that we can rule out the top end as the issue.

The problem then boils down to the crankcase and oil circuit. Please post some picture showing how the Vernatherm was plugged. Perhaps the folks here might be able to comment or rule that out as a cause. Post some pics of the cam and marks too. While you are at it, post pictures of everything as it is scattered out for good measure.

There is a reason the oil was hot (duhh). Oil cooler routing/flow stands out as a primary issue to be run to ground. Lube passages through everything, particularly returns, being next on the list. Pay particular attention to inspection of the oil pump.

Finally, as John stated, plan to re-instate the Vernatherm, unless something is wrong, properly plugged the oil temp is hard pressed to get above 165 or so, which is not hot enough to vent off condensation/water in the oil, particularly critical in the humid south. If the oil is hot with the Vernatherm removed, that's a problem for sure.
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

rowdy1
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Re: 520 Continental rebuild

Postby rowdy1 » Fri Oct 05, 2018 8:22 pm

I have been chasing what I thought was an intake leak thus a lean condition this whole time. I will clarify, I have an extra set of fresh cylinders to install on the engine now. The vernatherm was plugged by threading the passage between it inlet and outlet for the oil cooler so oil has to flow thru the cooler. (This is a sand cast block) There is no way to "undo" that, the seat for the plunger is now unusable. I have checked the temp in and out of the oil cooler and there is a 25* difference. Speaking of top end problems, what is a proper top ring gap? One of the cylinders that came off has a huge ring gap compared to the new cylinders, like double the gap! I have not measured it with feeler gauges yet but it looks huge. The motor did not have a lot of blow by. Ill try to post a few pics, I realize its hard to describe something correctly.

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Slidin Gator
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Re: 520 Continental rebuild

Postby Slidin Gator » Fri Oct 05, 2018 9:26 pm

It does not take a lot of blow by to overheat the oil, so you do want to trouble shoot the top end. Intake leaks by themselves do not directly equal high oil temp, but the resulting cylinder problems can.

There is a manual for the IO-520 on this board, nothing for an O-520:
http://www.southernairboat.com/pdf/aircraftengines/continental/520/IO-520%20_OV.pdf

Go to page 6-19 which shows the ring in groove clearance new at 0.004", service limit is 0.008" for all 3 rings. A piston that looks different is a red flag for sure. Just to clarify, I'm a Lycoming guy, Continental knowledge is limited to AV engines in general and this manual.

Reading manual on the oil temp control valve, it is pretty clear that the valve plugs the passage off to force oil through the cooler. The reason I ask for pictures is wondering if it is possible to restrict the port to the cooler with the plug? It's a long shot and would require worn bearings (something you do have) and/or a weak oil pump.

Check for a PM from me.
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

rowdy1
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Re: 520 Continental rebuild

Postby rowdy1 » Sat Oct 06, 2018 6:30 pm

Ive been cleaning and looking at parts all day. Here is what Ive found:
3 chrome cylinders--look like spider cracks
1 steel cylinder, nearly worn out cross hatch
2 unknown cylinders, smooth dull grey color
One cylinder has a bad spot down in the barrel you can see and feel.
3 different piston part #s, most of the top rings show a lot of heat, leopard spotted.
3 different main bearing manufactures and part numbers.
Lots of heli coils, 4 in sparkplug holes
#2 cylinder definitely running lean, sparkplug almost white
3 more cylinders very wet with oil
Lots of worn wrist pin bushings and even more worn out rocker arm bushings

I took all of the top rings off and squared them in the cylinders down 1 1/2 inches. End gaps were any where from .055 to a whopping .086.

BUILT FROM JUNK BY DRUNKS! Its a wonder it ran this long.

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John Fenner
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Re: 520 Continental rebuild

Postby John Fenner » Sun Oct 07, 2018 8:11 am

Bingo, the dull gray is nikosil, garbage, bet wear spot is up in the choke, ring ridge to bare steel, save the 3 channel chrome, as stated above, get the 10:1 Ross forged pistons or 648013 8.6:1 slugs, sounds like a real hack job but you are on the right track. Valve lash is adjusted by disassembling the hydraulic lifters and removing all oil and assembling virtually dry, wd 40 to not gall the plunger or bores, once back together rocker arm shall have roughly .028 to.110 lash for that engine, been a while, check specs in slidin gators link.
P.S. doubt cam timing is an issue, period....
I never finish anyth,,,.

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Slidin Gator
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Re: 520 Continental rebuild

Postby Slidin Gator » Sun Oct 07, 2018 8:34 pm

Rowdy,

I get the built from junk issue, it don't sound like a real fresh rebuild to me. But don't go givin us drunks a bad name!

I agree with John, try to save the channel chrome jugs for spare. Throw the gray ones away and think about chroming the worn out steel. Some of this might be lack of platform knowledge, but my thoughts from the Lycoming side:

Do you know if you have an IO or O-520, you never stated that? Just wondering if the IO-520 manual is applicable to what you have, John seems to think so. You stated earlier that there did not seem to be any valve preload when you disassembled, but noted there is nothing to adjust. Assuming Continentals are similar to Lycomings, you adjust the valve lash with the push rod length. On plane applications you have to order different length rods to tune it. I get it, less to go wrong once tuned, and it is possible to shorten the rods with enough time to kill.

What you want is a set of adjustable push rods, then it's just like tuning my old "P" cam Harley with the solid lifters in the living room of my old apartment. I adjusted those valve twice a year, motor cold in winter and motor hot in summer. Bastards kept the security deposit, something about an oil stain on the carpet.

I'm don't get a dime from these folks, but $25 each, $300 plus shipping will save you a lot of time tuning the motor in once it's all together.

https://southernairboat.com/phpBB3/viewtopic.php?f=47&t=71668&p=689843&hilit=adjustable+push#p689843
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

pax1ton
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Re: 520 Continental rebuild

Postby pax1ton » Mon Oct 08, 2018 8:11 am

The IO520 manual for the sandcast Block would be correct ,all O520"s were carb converted
as continental never produced a O520.

rowdy1
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Re: 520 Continental rebuild

Postby rowdy1 » Mon Oct 08, 2018 10:05 am

The motor is carb'ed, GMAC just rebuilt it last month. I have downloaded and printed the entire shop manual and the operating manuals. The block has already been hot tanked and the crank is going to the machine shop tomorrow to be polished and mic'ed. Based on what the crank cleans up at I'll have a starting point.
So far my working list includes: recon rods, all bearings, 10-1 pistons, rings, recon or rebushed rocker arms, adjustable push rods, oil pump gears and a complete engine gasket set.

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Slidin Gator
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Re: 520 Continental rebuild

Postby Slidin Gator » Mon Oct 08, 2018 10:07 am

Thanks pax1ton! That takes care of learning something new everyday for me today!
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

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John Fenner
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Re: 520 Continental rebuild

Postby John Fenner » Mon Oct 08, 2018 10:42 am

No real need for adjustable pushrod unless some radical valve and seat grinds are done, they should fall in spec.
I never finish anyth,,,.

flcracker9
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Re: 520 Continental rebuild

Postby flcracker9 » Mon Oct 08, 2018 10:57 am

John Fenner wrote: Valve lash is adjusted by disassembling the hydraulic lifters and removing all oil and assembling virtually dry, wd 40 to not gall the plunger or bores, once back together rocker arm shall have roughly .028 to.110 lash for that engine, been a while, check specs in slidin gators link


I just went through this on my IO-470 when I replaced all 3 cyls on the left bank. I tried depressing the plungers with a piece of wire while still in the case, and still couldn't get my lash right. I ended up trashing the rocker arm bushings and pins ( :violent1: $$$ lesson learned $$$ :violent1: ). I then removed the lifters and completely disassembled them (had to replace 2, they were pitted badly on the face), being careful to make sure the plungers were completely bottomed out, prior to reinstalling them in the engine (I coated all lifter parts with camshaft assembly lube?). I went a step further and had my pushrods converted to adjustable rods (Gary Barber did this for me), and set my lash at .090, and all is well after that.
12' Open Palm Beach, IO-0470-L 260hp, 72" NGQ

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John Fenner
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Re: 520 Continental rebuild

Postby John Fenner » Mon Oct 08, 2018 11:09 am

You have to take them apart and clear all oil from them, if too tight, you knock the tips out of the tubes and trim the tubing to suit.
I never finish anyth,,,.

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Slidin Gator
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Re: 520 Continental rebuild

Postby Slidin Gator » Mon Oct 08, 2018 5:14 pm

This is from page 5-7, covering the lifters with instructions on disassembly & inspection.

Image

On the subject of pushrods and valve lash, that is a lot wider lash adjustment range vs. Lycoming, so I can imagine that adjust-ability is less of an issue.

This statement seems to stand out to me:
rowdy1 wrote:It is supposed to have a 661 cam. It and the lifters show absolutely no wear. Honestly there didn't seam to be much lash at all before dismantling. There is nothing to adjust so im not sure how you would change that.


No valve lash/load at tear down seems like a lifter problem to me??
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

rowdy1
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Re: 520 Continental rebuild

Postby rowdy1 » Mon Oct 08, 2018 7:55 pm

It is a 661 cam. There were several rockers that had slight preload on them even after rolling around to the round side of the cam. Enough that I had to tab the rocker shaft out with a brass punch. NOT beat out, tap out.

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Slidin Gator
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Re: 520 Continental rebuild

Postby Slidin Gator » Mon Oct 08, 2018 8:23 pm

But did some of them have no preload, as in rocker arm loose with clearance on valve stems?

Some preload with tap out of shaft sounds normal. But loose rocker arms (on round side of cam) would indicate leaking lifter. Do you know which cylinders match which lifter and match which conditions? Inspect them all, but in particular the leaking ones.

Page 6-7 covers inspection. The check valve should hold pressure.

Image
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.


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