Stripped Plug and Low Comp
Posted: Thu Sep 21, 2023 5:07 pm
by Weatherpilot
So, In my new to me Sonex I was changing plugs and doing a condition inspection. (with my mechanic) Cyl #3 has 4psi and can hear air escaping from the exhaust. Bad/dirty/funky exhaust valve I’d guess. Also, some previous person ham-fisted the top plug in pretty much stripping it. I want to replace the head on that side to fix the stripped plug. I know there are repair kits things that can be used but I would feel better with a solid head. So while I’m at it should I do both? The cylinders are in good shape. Borescoped and looking good.
What is a good source for new heads? Sonex? Other? Any recommendations welcomed.
Thanks,
Greg.
Re: Stripped Plug and Low Comp
Posted: Thu Sep 21, 2023 6:36 pm
by Bryan Cotton
I’d repair the head with timeserts.
viewtopic.php?f=7&t=3948&p=29996&hilit=Timeserts#p29996
But if I was buying new heads, I’d go to Sonex.
Re: Stripped Plug and Low Comp
Posted: Thu Sep 21, 2023 6:50 pm
by daleandee
Bryan Cotton wrote:I’d repair the head with timeserts.
http://www.sonexbuilders.net/viewtopic. … rts#p29996But if I was buying new heads, I’d go to Sonex.
Agreed! Do the timeserts and lap/grind the valves as needed. Save the real money for gas … 8~)
Re: Stripped Plug and Low Comp
Posted: Thu Sep 21, 2023 7:41 pm
by Bryan Cotton
It’s my understanding that the timesert is better than a solid head. It’s a steel insert locktited in, and the plug replacements are all steel on steel. If I had known about it when we built our Aerovee I would have done it proactively. Since then I bought the kit and will do it at overhaul.
Re: Stripped Plug and Low Comp
Posted: Fri Sep 29, 2023 10:27 am
by Weatherpilot
So I have decided to replace the head with the stripped out plug hole and sticking valve. Sonex has them for about $550 + shipping. I looked around and see that MOFOCO and EMPI have heads for about half that cost. MOFOCO will even do second spark plug for $100 additional. Anyone opt for the MOFOCO or EMPI heads? Experiences? Which one do I get for the Aerovee? Any help appreciated.
Greg.
Re: Stripped Plug and Low Comp
Posted: Sat Sep 30, 2023 9:32 am
by bvolcko38
MOFOCO heads came with early Aerovees. I don’t know why Sonex switch suppliers.
Re: Stripped Plug and Low Comp
Posted: Sat Sep 30, 2023 10:15 am
by Area 51%
bvolcko38 wrote:MOFOCO heads came with early Aerovees. I don’t know why Sonex switch suppliers.
CB Performance heads can be found on an early Aerovee engine. The factory prototype Xenos came with these. Very nice high quality heads, but don’t tell CB what you are using them for.
Re: Stripped Plug and Low Comp
Posted: Sat Sep 30, 2023 12:05 pm
by Weatherpilot
Which type head do I get from these places? They have several variants.
Re: Stripped Plug and Low Comp
Posted: Sat Sep 30, 2023 3:06 pm
by Area 51%
Weatherpilot wrote:Which type head do I get from these places? They have several variants.
92mm cylinder openings with 40mm intake valves.
Re: Stripped Plug and Low Comp
Posted: Sun Oct 01, 2023 12:23 am
by kmacht
Even if you replace the head you should still consider installing timeserts. The aerovee tends to build carbon on the end of the plug and when you go to remove it that carbon binds the plug and strips out the aluminum threads in the head as the plug comes out. It’s likely that the original builder didn’t ham fist the plug in and instead you ended up stripping the threads yourself when you tried to remove the plug with the carbon buildup. There isn’t really any fix when the carbon starts to cause the plug to bind other than pulling the head and trying to remove the carbon buildup before unscrewing the plug further. The timesert essentially turns the spark plug threads from aluminum to steel and since the steel is harder than the carbon buildup it will push the carbon off when you unscrew the plug. I borrowed the timesert kit from a fellow builder and put them in my heads during a rebuild. It was very easy to do.
Keith
#554
Re: Stripped Plug and Low Comp
Posted: Sun Oct 01, 2023 6:21 pm
by pappas
I developed a burned valve in my original MOFOCO heads. After doing the research as well as speaking to Sonex, I decided to replace them with EMPI heads and bought them from Sonex already machined for dual plugs.
Once they arrived, my friend did a 3-angle valve job and ported and flowed them. I reinstalled the original rocker arm assembly. The engine ran like never before. Don’t use the MOFOCO’s. The EMPIs are superior.
Re: Stripped Plug and Low Comp
Posted: Tue Oct 03, 2023 7:21 am
by pfhoeycfi
I’m doing the first condition inspection since getting the AWC, just less than 50 hrs TT, and I had a difficult time removing several sparkplugs that were removed an reinstalled quite easily at 5 hrs. Later today I’m gonna scope the holes and have a look. Assuming I need to install timeserts, can anyone say for sure if its the M12 x 1.25 15 mm or 17.5 mm insert that is required? I see both lengths mentioned in different posts. Not happy about having to pull the heads on a engine that is running great. I’m also curious if this is a warranty issue. Any advice or warnings for installing timeserts?
peter
Re: Stripped Plug and Low Comp
Posted: Tue Oct 03, 2023 9:22 am
by kmacht
15mm is what I used and they worked fine. The process really is simple and fairly foolproof. The factory really should be installing them as standard features when they modify the heads for the second set of plugs. There are a few air cooled vw online stores that will rent you the installation kit to save you some money. I think it’s under $50 to rent the install kit plus the cost of 8 inserts.
Keith
#554
Re: Stripped Plug and Low Comp
Posted: Tue Oct 03, 2023 10:04 am
by pappas
In my original MOFOCO heads, I installed TimeSerts for the same reasons everyone else does. The MOFOCO aluminum casting is just softer than the EMPI and the plugs strip easily. Doesn’t matter if you use plug lube or not. Yes, Sonex should have them installed when they drill for dual plugs.
The TimeSerts worked great. I did not even have to remove the heads to install them. Just rotate the prop to get both valves closed, heavily grease the drill and tap tool, and install them according to directions. The grease captures any shavings from the drill and tap procedure. A machinist friend of mine taught me that trick and has been using it for decades in Harley engines. Make sure to blow out the cylinder after each insert and scope them just to be sure. I had no issues.
Re: Stripped Plug and Low Comp
Posted: Tue Oct 03, 2023 6:17 pm
by pfhoeycfi
Here are a few photos of #3. Ugly. # 3 runs the hottest. #4 has a little of this as well. #1 & 2 are very clean in comparison. The damaged thread shown is for the bottom plug. The top thread is clean. Note the small collection of scale at the edge of piston on the cylinder wall…it is right below the thread and presumably broke free of the plug when I loosened it.
I plan on pulling the heads to install the timeserts and take a closer look. I am very curious to know why 4 cylinders can looks so different. Comments and observations welcome.
peter
Re: Stripped Plug and Low Comp
Posted: Wed Oct 04, 2023 1:45 am
by Weatherpilot
Weatherpilot wrote:Cyl #3 has 4psi and can hear air escaping from the exhaust.
Update to my dilemma:
I removed the valve cover thinking maybe the exhaust valve wasn’t closing all the way. Nope, valve looks like it is operating normally when turning the crank by hand. Perhaps some carbon or something is allowing pressure to escape? Going to borescope to see what is in there. My next step is to start it up and see if it improves. It has been sitting for a while so maybe a start and lean idle might help?
Re: Stripped Plug and Low Comp
Posted: Wed Oct 04, 2023 12:12 pm
by daleandee
Weatherpilot wrote:
Weatherpilot wrote:Cyl #3 has 4psi and can hear air escaping from the exhaust.
Update to my dilemma:
I removed the valve cover thinking maybe the exhaust valve wasn’t closing all the way. Nope, valve looks like it is operating normally when turning the crank by hand. Perhaps some carbon or something is allowing pressure to escape? Going to borescope to see what is in there. My next step is to start it up and see if it improves. It has been sitting for a while so maybe a start and lean idle might help?
You can pressurize the cylinder to find where the leak is coming from. It’s easy enough to say it is the exhaust valve but I’ve found intake valves to leak when carbon or lead got in the way of the valve closing. If it is a valve you may be able to stake the offending valve and get better compression numbers.
FWIW,
Dale 3.0 Corvair/Tailwheel
Re: Stripped Plug and Low Comp
Posted: Wed Oct 04, 2023 12:41 pm
by kmacht
Simple question but after pulling the valve cover did you also check the rocker to valve stem clearance and if so, what were they at? The valve stems tend to stretch a little bit over time and can close up the .004-.006 gap that is supposed to be between the valve and rocker arm when fully closed. If you have no gap on that valve it could be holding the valve just slightly open. If the gap is much bigger than .006 it could be that you have a piece of carbon holding the valve from completely closing.
Keith
#554
Re: Stripped Plug and Low Comp
Posted: Wed Oct 04, 2023 9:36 pm
by Weatherpilot
Good recommendation. I will be adjusting the valve clearances per the Aerovee assembly manual and then run the engine to see what that does. Like I said in the original post - this thing ran fine but did sit for 10 months in tiedown. Going to run it and see if things improve.
Thanks for all the great advice.
Greg.
Re: Stripped Plug and Low Comp
Posted: Sun Oct 15, 2023 10:30 am
by Weatherpilot
Did the valve adjustment yesterday. I was surprised to discover the valve covers although safety wired were finger tight on the bolts that hold the cover. After the valve adjustment cleaned the covers and replaced the gaskets with new ones. Also put in new grommets on the bolts as the ones that were in there were the wrong ones and broke apart when I removed the valve covers. Discovering a lot of loose things on this motor. Plugs finger tight. Other items not tightened down properly too. Going to keep going over this engine with a discerning eye.
Updates to continue.
Greg.
Re: Stripped Plug and Low Comp
Posted: Thu Oct 19, 2023 9:10 pm
by mike.smith
Hi:
I have the Timesert tool and loan it out often. PM me if you are interested. Like Keith said, it really should be done before any heads are sent to a buyer.
As far as compression, the VW is a very loose engine. It was designed to be simple, with simple tolerances. It will tolerate a lot of slop. I never get 4 cylinders to pass a compression check at each annual. But every time, I fly around the pattern to warm everything up, and do the check again, and guess what? The “bad” cylinder is always good. You don’t run your engine cold, so you really shouldn’t care too much if you have good compression with a cold engine. Compression tests are notoriously inaccurate anyway.
https://resources.savvyaviation.com/wp- … ession.pdf
Treat a VW with the respect an engine deserves, but don’t treat it like a fine watch. That’s something it will never be
Re: Stripped Plug and Low Comp
Posted: Fri Mar 29, 2024 12:11 am
by Weatherpilot
Weatherpilot wrote:So, In my new to me Sonex I was changing plugs and doing a condition inspection. (with my mechanic) Cyl #3 has 4psi and can hear air escaping from the exhaust. Bad/dirty/funky exhaust valve I’d guess.
Well, after this and completing the condition inspection - ran the engine. Got it up to temp. Shut it down and did another comp test.
Now reading 80/76 along with the other cylinders being in the same ballpark.
Thanks for all the info and help.
Greg.