Dropped a valve

[saygold]

My car is a 1966 230SL German version (originally purchased in Hamburg).  It is a "driver", but with the interior and body work completed several years ago.  It has been updated with 3.92:1 rear axle ratio and rear disc brakes, and the interior was redone with leather.  I have both tops.

I rebuilt the cylinder head of my 230SL about 3 years (and about 1500 km) agowhen the valve seals started to go bad.  The car has about 130,000 km (I have owned the car since 1986 so I am sure it is accurate).  I went on a short run several days ago, and had a bad knock in the engine when I came off the freeway.

To make a long story short, the collets came loose on #5 intake valve and it hit the piston crown.  The valve broke off the stem and both are stuck in the intake area.  I took photos of the head and engine block but have not posted the remaining ones.

I believe the broken valve can be removed and the cylinder head repaired fairly easily.  I think the piston will have to be replaced.

The engine compression was good for all cylinders after the head was rebuilt.  Should all the pistons be replaced or just the damaged one? 


Thanks in advance for your recommendations.

Ken Deter
1966 230SL (euro, 4-speed)

[ja17]

Hello Ken,

It's hard to say if the bottom end of is in good enough shape to last without a overhaul. Fortunately the damaged piston is #2 and you will be able to remove it along with the rod by droping the steel oil pan. Carefully examine the piston, rod bearing, and crank when you have it apart. Check the piston ring groove width. When they become too wide the piston  ring can twist and break.

If you need to replace all the pistons, you would probably want to do a major overhaul and order oversize pistons so that the cylinders could be bored out to remove any wear. The piston assemblies will be the single most expensive parts of a major overhaul.

[JimVillers]

Ken .... I had a similar problem with my 190SL years ago.  After repair, the cam bolt came loose, the cam slid off of the bearings and a piston shoved a valve up and broke the cam shaft.  I replaced the cam shaft and drove 1000 miles home.  The engine ran for 15 more years without issue.  Unless the piston shows a crack, I would feel good about just fixing the head.

[saygold]

Thanks for your quick response and comments.

The dropped valve is on the second cylinder from the fire wall.  I always considered it to be #5 - sorry about the mistake.

I will start on the engine now following Joe's comments.

Best regards,
Ken Deter
'66 230SL -4sp, euro

[lurtch]

Hey Ken - - If you do a complete overhaul,  be advised: the  oversize piston set of six will cost you close to  $ 1,800.  I learned this lesson earlier this year while doing the bottom end on my M130. Also, there were very difficult to locate at that time. The correct high dollar  ones are MAHLE. After an exhaustive search for the best price by myself and my engine builder I caved in an bought them from ADSITCo in Mich.

Good Luck, Larry in CA

[stickandrudderman]

A good way to check for rod damage before disassembly is to check the piston height with a DTI. Do it for all 6 at TDC and you'll soon spot any anomaly.
Next you should check the cylinder wear with the correct micrometer and with pistons at BDC.
If all is within tolerance and there is no sign of any shrapnel damage or scoring to the No 5 cylinder then you can just replace the one piston.
However, if it were my engine I would bite the bullet and do a complete overhaul; you've got to take the engine out anyway.
(I have seen in my time a less than scrupulous mechanic remove the broken valve stem from the top of a piston and plug the hole with a self-tapping screw. Believe it or not, the engine ran perfectly although for how long I don't know.

[saygold]

The engine was running, albeit with a knocking sound, when I shut it down.

The engine number is 127.981-10-128xx; the car number is 113.42-10-16xxx.   The engine is still standard.  Based on information available in the internet, including SLS, the pistons are the 3rd version with 3 piston rings.  I will confirm this when i pull the engine. 

If i just change #5 piston, does it make sense to change the piston rings on the remaining ones?  Likewise, the crankshaft bearings, etc (after confirming for wear)?

Ken Deter
'66 230SL (4-speed, euro)

[stickandrudderman]

You'll find (I think) that piston rings sets are hard to come by, so you'll be looking at new pistons anyway.
An engine of that age still on standard pistons it would alsmost certainly benefit from a rebore and oversize pistons.
Do the measurements and see.

[Eminent]

The dropped valve is on the second cylinder from the fire wall.  I always considered it to be #5 - sorry about the mistake.

I think you are correct with the numbers. The #1 cilinder is the cilinder which is most in front of the car.
If you are looking at the mark on the distributorhouse (which marks the firing for the #1 cilinder)  and you follow the cable to the sparkplug you will see that the #1 is in front.
Or, and thats easier, look in the Haynes manual at page 98.

[Peter van Es]

From the tech manual, restricted section! Join for full access!

Peter

[saygold]

Thanks for everybody's comments.  It was #5 intake valve that was dropped.  I found one of the split collets but not the second - there was some flattened pieces but I could not confirm what they were.

The engine and transmission have been pulled and I am waiting for a few pieces to arrive before tackling the engine rebuild.  I obtained a used piston, but could not get replacement rings individually.  I received a new piston with rings and wrist pin yesterday.  Still waiting on the valve and guide to repair the cylinder head. 

I have been cleaning the engine and transmission compartment (it is amazing how much had built up) and have removed the original firewall pad using elbow grease and a scraper. 

Hopefully, I can get it completed in a week or so.  I will be following the Haynes and BBB manuals and searching the forum as I go along.  I may be asking more questions as well!

Ken Deter
230SL (euro, 4-speed)

 

[mbzse]

I do have a set of standard size piston rings which I can part with. These fit our Pagoda 230 and 250 engines (81,97mm dia)
i.e. M127 and M129
/Hans in Sweden

You'll find (I think) that piston rings sets are hard to come by....

[saygold]

Thanks for your comment.

I obtained a used standard piston from Chuck Taylor.  I decided not to install it however. 

Best regards,
Ken
'66 230SL (euro, 4-speed)