bend a valve by being one tooth off on the chain? - Page 2 - PeachParts Mercedes-Benz Forum

t walgamuth · #16 05-18-2008, 04:57 PM

Quote:

Originally Posted by stevebfl

It would be very unlikely to bend both intake and exhaust valves. Do you have the cam held in place at TDC when applying the air? Or have you removed the rocker arms?

After further thought I have come to this conclusion myself. Its a good thing.

Tom W

t walgamuth · #17 05-18-2008, 04:59 PM

Quote:

Originally Posted by stevebfl

It is also real posible that carbon of rust has fouled the valves enough to pass compressed air.

Yes. I am hoping for this.

Its my 59 Ferrari 250 gt pf coupe. I have gotten valve event information but I am not convinced it is correct.

I am not going to pull a head just yet....not until I am more nearly 100% sure I know what I am looking at.

Tom W

t walgamuth · #18 05-18-2008, 05:00 PM

Quote:

Originally Posted by troylatif

I would have to agree with the post that mentions stuck valves. If a valve is stuck, then sure it'll collide unexpectedly.

I had this experience in rebuilding my m110 in my w123 280e. In the end I just took it to a shop with all the new guides, valves, and grease of choice, and let them have at it. Came out real nice.

But with regard to timing, I'd say your best bet is to get the no 1 piston at TDC before setting the valve train over it. In that case, I'd take a depth gauge and get the true TDC position. You'd be miraculously suprised at how the TDC on the damper is even ~0.3 degrees off due to deformation in the disc material or in the mounting hub. I was quite surprised that a slight hot burning issue was caused by none other than a 0.3 degree offset from the true TDC. That was after getting the whole thing put together!

Anyways, yes, you can get valve piston collisions due to a misplaced chain. Check the specs on your engine so as to when the intake and exhaust both open and close. Take your cam gear and measure the radius. Get the circumference. Take the link to link distance, and then divide the gear circ. by the link to link distance. This is how many links can sit on the gear. Then divide 360 degrees by that number and this is how many degrees offset you will have as a result of misplacing the chain by one link. CHeck this against your "valve opens at" measurement and there you have your answer.

If the calculation gives you a number that is greater than your book's number, then you very well could have bent valves this way. I bent 4 intake and exhaust that way before saying "f' it, i'm buying all new valves and sending it to a pro".

-Troy

Thanks. I will plow through all these calcualtaions and see what I come up with.

Tom W

t walgamuth · #19 05-21-2008, 11:39 PM

After much deliberation I decided to pull the right side head. It took about 7 hours instead of the two that I estimated!

The head has studs and nuts and there is only one nut per head that is not shrouded either by the head structure or the hairpin valve springs! This engine makes a Mercedes look like a flathead four for ease of wrenching. I spent about 20 minutes taking material off my wrenches so I could remove the nuts shrouded by the head structure on the inside of the 60 degree V.

I found that all of the exhaust valves have touched the tops of the pistons enough to knock the carbon off the valves. I will have my favorite machinist break them down and check to see if they are bent.

A place in the head gasket came apart too so it will require a new one.

Oh, well, now I'll be able to sell it with a fresh valve job!

Oh yes, I could have avoided it all if I had not tightened down the rocker assemblies when turning the engine to time it.

Tom W

Chas H · #20 05-22-2008, 10:20 AM

Quote:

Originally Posted by t walgamuth

Yes. I am hoping for this.

Its my 59 Ferrari 250 gt pf coupe. I have gotten valve event information but I am not convinced it is correct.

I am not going to pull a head just yet....not until I am more nearly 100% sure I know what I am looking at.

Tom W

Why didn't you say it was a Ferrari engine earlier? Or did I miss that? Being off a tooth on a Ferrari engine could indeed cause some valve collisions.

t walgamuth · #21 05-22-2008, 06:51 PM

I took it in this afternoon dressed to work. I worked with my favorite machinist's son on the valves. They were tricky but we got them all out. No bending was noted and they have minimal wear. A light dressing of the edges and seats will make them like new. The guides do not show any wear either.

I will work on removing the other head perhaps some tonight and tomorrow. I am considering dropping the pan and pulling one piston and rod so we can examine the rings. We are thinking the bearings will probably be good. The bores we know are in spec because we measured them when I originally removed the heads for the head gaskets.

I am feeling pretty good about the old girl now.

Tom W

t walgamuth · #22 05-23-2008, 08:23 PM

Today I got off the second head in record time without breaking any studs or anything similar.

Upon closer examination by my favorite machinist he found quite a lot of wear on the intake valve stems. Also the second head has a lot of guide wear so it will be new intakes and quite a few guides. Tomorrow he will grind the valves that are good and we'll see if any others need replacing for being bent.

I think maybe the air filters were loose on one or two of the carburators and let in dirty air.

I'll probably try to pull a piston and one rod tomorrow so he can measure the rings.

Ha! I'm sure glad that none of the valves were bent!

Tom W