Author Topic: Test post rebuilt head???  (Read 5529 times)

erickmarciano

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Test post rebuilt head???
« on: April 06, 2016, 23:57:19 »
 Hi is an accurate way of testing a rebuilt cylinder head by putting water in the combustion chamber and using air gun at 100 psi in the runners to see if there's bubbles I got a few valves with bubbles ?
Thanks
1994 E500 W124
1971 280sl
1989 Porsche 930 coupe
1988 e30 m3
2001 ducati mh900
2006 ps1000
1962 Vespa GS160

Tyler S

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Re: Test post rebuilt head???
« Reply #1 on: April 07, 2016, 02:25:17 »
You have the right idea but you need to be applying the pressure in the combustion area and fill the runners with liquid. Not something you can do at home. When the engine is running, the combustion pressure is what helps seal the valves closed. If your just double checking, you can put the head on its side and fill the runners with "kingsford" and look for wetness around the valve seats. Your machine shop should have done a pressure test before it left their shop.
1968 (67) 250sl. 4 speed manual. DB180 Silver
1955 220 Cabriolet A. White Grey
2019 E450 Wagon. Majestic Blue
1936 Ford PU Flathead V8. Creme on tan interior.
1989 Volkswagen T3 Westfailia Campmobile. Dove Grey (blue)

Benz Dr.

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Re: Test post rebuilt head???
« Reply #2 on: April 07, 2016, 03:48:59 »
I use a vacuum tester. No liquids needed and it's very quick and easy to use. If my tester doesn't pull 17 inches of vacuum the valves are leaking.
1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
Dan Caron's SL Barn

1970  3.5 Coupe
1961  190SL
1985   300CD  Turbo Coupe
1981  300SD
2013  GMC  Sierra
1965  230SL
1967 250SL
1970 280SL
1988 560SEC

Tyler S

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Re: Test post rebuilt head???
« Reply #3 on: April 07, 2016, 04:16:38 »
Dan, where are you applying the vacuum? Wont the valve guides cause it to leak down? Or are you using it over the valve on the combustion side?
1968 (67) 250sl. 4 speed manual. DB180 Silver
1955 220 Cabriolet A. White Grey
2019 E450 Wagon. Majestic Blue
1936 Ford PU Flathead V8. Creme on tan interior.
1989 Volkswagen T3 Westfailia Campmobile. Dove Grey (blue)

ja17

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Re: Test post rebuilt head???
« Reply #4 on: April 07, 2016, 05:25:02 »
I always have the machine shop grind the valves and seats and install the valve guides. Then I have them return the head to me apart. I do the final lapping of the valves with some compound then with blue layout dye. When all is checked out, I install the valve seals and assemble the cylinder head (springs, valves and seals).
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1982 300TD Wagon turbo 4spd.
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback

erickmarciano

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Re: Test post rebuilt head???
« Reply #5 on: April 07, 2016, 11:09:26 »
Yes that's what I did . I took it apart to double check.
Thanks for the advice
He did use a suction cup on the combustion side
There are a lot of mixed thoughts of lapping a fresh cut seat and valve
It does sound like a good idea
Thanks again
« Last Edit: April 07, 2016, 13:08:11 by erickmarciano »
1994 E500 W124
1971 280sl
1989 Porsche 930 coupe
1988 e30 m3
2001 ducati mh900
2006 ps1000
1962 Vespa GS160

Benz Dr.

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Re: Test post rebuilt head???
« Reply #6 on: April 07, 2016, 19:33:56 »
Dan, where are you applying the vacuum? Wont the valve guides cause it to leak down? Or are you using it over the valve on the combustion side?

It's a foam covered disc that goes over the combustion chamber. I install everything including the spark plug so there are no leaks. This tool uses compressed air and when you pull the trigger it shoots air out of a small orifice that sits right next to another small orifice. This creates a vacuum that will evacuate anything that will hold a good seal. You can also do individual valves if your application will allow it. I bought it from Souix Tools about 15 years ago.

 One time a small piece of dirt fell on to a valve seat during assembly and the tester picked it up right away. I'm sure it would have cleared right away but it will work that well.

You can also vacuum complete cylinders with pistons installed or the complete system with cylinder head mounted. The nice thing about this tool is you don't need to have a running engine to test the condition of the head like you would while doing a compression test. As long as you can turn the engine by hand you will be able to get a reading. Often the readings will be much lower for a complete system due to the larger area being vacuumed and readings of less than 10 inches are common.

I tried using an air pig on a remote test and it didn't work so I think you would need a bottle of compressed air to make it work right if you are not in your shop. I don't use it as much now that  have my machine shop assemble my cylinder heads.
1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
Dan Caron's SL Barn

1970  3.5 Coupe
1961  190SL
1985   300CD  Turbo Coupe
1981  300SD
2013  GMC  Sierra
1965  230SL
1967 250SL
1970 280SL
1988 560SEC

erickmarciano

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Re: Test post rebuilt head???
« Reply #7 on: April 12, 2016, 01:50:44 »
Hi guys got the scare of my life.
installed the rebuilt head saturday
Went for a 10 minute ride got home engine hot I re torqued the head than put the valve cover back on  and left it at that.
Today I moved the car out of the garage and It ran real bad
My compression readings before were 140-150
Did a compresion test today and got under 100 and #2 at 10 psi
Toke the valve cover off and the valves were super tight.  Slacked the 2 valves at #2 and did a quick compresion test and got 140 psi. Can start breathing again.
Why do you think the valves got tight with a 10 min ride and a re torque?
Thanks
1994 E500 W124
1971 280sl
1989 Porsche 930 coupe
1988 e30 m3
2001 ducati mh900
2006 ps1000
1962 Vespa GS160

Tyler S

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Re: Test post rebuilt head???
« Reply #8 on: April 12, 2016, 03:22:15 »
Since you brought the headbolts to their proper full torque after your inital run, you also in effect lowered the camshaft closer to the rockers. The cam towers are held by the head bolts.  ;)
There is also a little bit of a break-in.
Adjust your valves one more time when its stone cold.
1968 (67) 250sl. 4 speed manual. DB180 Silver
1955 220 Cabriolet A. White Grey
2019 E450 Wagon. Majestic Blue
1936 Ford PU Flathead V8. Creme on tan interior.
1989 Volkswagen T3 Westfailia Campmobile. Dove Grey (blue)

tel76

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Re: Test post rebuilt head???
« Reply #9 on: April 12, 2016, 11:45:01 »
After re-torqueing (hot engine) a cylinder head you should always check and re-adjust the valve clearances (cold engine). 
Eric

Benz Dr.

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Re: Test post rebuilt head???
« Reply #10 on: April 12, 2016, 14:57:14 »
Agreed. However, I would keep an eye on number two cylinder. A re-torque shouldn't change the valve lash that much unless the head bolts weren't that tight to begin with. I'd be more concerned about a possible worn out ball stud adjuster.
1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
Dan Caron's SL Barn

1970  3.5 Coupe
1961  190SL
1985   300CD  Turbo Coupe
1981  300SD
2013  GMC  Sierra
1965  230SL
1967 250SL
1970 280SL
1988 560SEC

ja17

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Re: Test post rebuilt head???
« Reply #11 on: April 12, 2016, 21:44:49 »
Most likely parts settling in place.  If you did not keep the rocker arms in their exact location and the pressure pads in position and oriented the same direction, then the "wear patterns" are no longer matched up to other wear patterns. According to BBB, torque head during assembly and adjust the valves. After first warm-up re-torque the head and adjust valves again on the cold engine. Lastly re-torque head and adjust vales on a cold engine after some mileage. Don't forget to always relieve the pressure in the cooling system before beginning the re-torque process. During assembly the head torque procedure is done on a cold engine, re-torque the head hot and adjust the valves cold on the later re-torques.
« Last Edit: April 12, 2016, 21:49:54 by ja17 »
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1982 300TD Wagon turbo 4spd.
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback

erickmarciano

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Re: Test post rebuilt head???
« Reply #12 on: April 12, 2016, 21:47:51 »
Thanks guys
Joe when you say some miles you mean
Like 1-2000 mi?
1994 E500 W124
1971 280sl
1989 Porsche 930 coupe
1988 e30 m3
2001 ducati mh900
2006 ps1000
1962 Vespa GS160

ja17

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Re: Test post rebuilt head???
« Reply #13 on: April 12, 2016, 21:50:44 »
Standard practice is around 500 miles Erick,
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1982 300TD Wagon turbo 4spd.
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback