Red Rocket set to live again

[Benz Dr.]

The Red Rocket may see the roads again soon once all repairs are made. During a brief slower time in the shop, time became available to remove the engine and see why water was leaking out between the block and the head.
 
 '' Well, the block isn't warped like I first thought and it appears to be the cylinder head. I would have been unhappy to have spent all that time pulling the engine but during the tear down I decided to look things over a bit closer '' reported the Benz Dr.
'' The engine seemed to be low on compression even though everything was new in there and all the numbers were very even - it was just 25 PSI lower than it should have been. After measuring the amount the pistons sit level with the block I found that they are at least .50 mm BELOW the block parting surface. They can stick out of the block anywhere from .20 to .70 mm so I guess I'll get the block milled about 1 full mm  That should bring the compression back up into the 165 PSI range where it belongs '' stated the Dr.

'' I'll definately watch all the fluid leves this time '' he added.


Daniel G Caron

[Cees Klumper]

Congratulations Dan - but how come the rebuild did not result in the proper compression - are the pistons too 'short' ?

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[mdsalemi]

Dan,

I'll be happy to see the Red Rocket once again, uncovered and under its own power....perhaps you can take a short tour to my side of the border.  I know a great bakery I can take you to.

As for your engine, an alternative is to solicit some more bread and butter work on newer cars, to help you pay to ship the darn casting to Metric for a proper rebuild!   You have seen for yourself how well they do, and it does seem to go well in Signal Red, too, eh?  Then you can concern yourself with the minutae of getting the rest of the car in order!!



Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored

[Benz Dr.]

Hi, Cees.
I bought the pistons a long time ago and really didn't notice anything unusual when I installed them. This engine is not your normal example and everything is my own special brew. There are no specs on what I'm doing but the new pistons are shorter than standards. I think they lower them about 1 mm in case you need to deck the head. I was at the machine shop this morning and my guy said that even that much will make a big difference.

 The engine rebuild took me a few years to do and some of this R&D takes a bit of trial and error to get right. I knew as soon as I fired it up that it wasn't what I wanted but was willing to live with it since I had no help to pull the engine back out. It would have run OK but it also would have been down on power. I'm hopeing it should be as strong as a 280SL from 2.5 liters.

All this will be valuable information when I have it finished and will go into the memory banks for new rebuilds. There's a lot to engine building and it's very easy to make small mistakes if you don't know about some small detail. Following the workshop manual is critical for this type of work. At the very least you need to maintain minimum specs. Expirience is really important and every build is different. Taking into account that some parts are getting harder to find and more exspensive good castings like cylinder heads are worth having around. Knowing the limits that you can machine something is also pretty important and parts that are near the maximum are not as valuable. Most things in and around the engine seem to have about a 1 mm maximum stock removal.



Daniel G Caron

[Cees Klumper]

Hi Dan - just today I came across a 1972 280 SE engine that someone was selling on Dutch Ebay. I agreed to buy it from him (will I ever learn?) and when I went to pick it up this afternoon, he told me to "make sure you deck the head, that is something one always should do when the head is off anyway". Most of the time these heads are fine as they are I'm sure, and I wonder how many heads have been planed without any good reason. New ones (if still available) are about $2,500. As far as I know, they won't warp unless the engine is allowed to overheat and/or the head gasket fails?

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[Benz Dr.]

All good points really. The head can warp from over heating but it can also warp if you don't tighten it down properly. Most heads have corrosion problems that seem to be worse on older cars. If coolant leaks by the head gasket and gets into the cumbustion chambers it will really eat away at the aluminum - sometimes this destroys the head completely.

I spent a few hundred dollars and bought a straight bar for checking blocks and heads. I won't sell or ship anything that isn't straight or flat. Anything over .003'' is considered warped and would beed to be cut lightly.
Some places will heat the head and then straighten it - I've not had this done - only machining. The book says that the top of the head has to be straight too and parallel with the bottom surface but that's not what I've found. As long as the cam will turn by hand after the head is bolted down it won't size up or start to bind. Very few old heads are flat on the top surface and frankly I don't care about that as much as the parting surface which has to be very flat.
The main thing is how thick the head is - ask how thick it is, just don't hope for the best and end up buying a door stopper.
 Next thing is condition - it can be all greasy and covered in dirt with rusty old valves and springs yet be a perfect example or it can look great and be junk. Heads that are near the minimum thickness will probably have very worn valve guides and/or seats. These can be replaced but at some cost and this needs to be considered carefully.
Other problems I've seen are corroded water jackets, stripped spark plug holes, missing parts, cracks in the head ( very rare ) and broken manifold studs. All of these things can be fixed, new valve guides installed, valve seats put in and water jackets repaired with new inserts. Almost everything is fixable as long as you start wih something useable.
Refer to the workshop manual for minimum and maxium specs and know what you have BEFORE you start any work. Remember, a standard sized cylinder bore may need maximum over size pistons just to clean out so buy your pistons after this is known and not before. This can be a costly mistake and can hold you up for months if it's a rare size or aplication and you have to wait for new parts or suddenly have to find them. Make sure the parts are actually available BEFORE you decide to rebuild.


Daniel G Caron