104.980 head work - Page 2 - PeachParts Mercedes-Benz Forum

duxthe1 · #16 05-20-2017, 02:13 AM

Quote:

Originally Posted by MAG58

Also do you have any concerns with the lifters pumping down at high RPM?

I haven't really pushed the engine at high RPM enough to notice it but I thought I'd bring up something that you may not be aware of. Our 104.980 engines came with a very heavy lifter. 82 grams heavy. MB updated the part twice, 67 and then 52 grams by late '94. The late parts are backwards compatible. Taking 30g out of the lifter may significantly help. FWIW, the newer 6.3L engines use a lifter that looks identical in dimensions to the late 104 lifters, but I'm unsure their weight. There is also an updated lifter for that engine with a carbide face.

I've been evaluating the cam timing events and rethinking how I'm going to install the cams. Stock the cams have a LSA of 102.75 advanced and 118.75 retarded. With my longer duration intake I'm planning to open the intake valve several degrees earlier and open the exhaust valve a few degrees later. There is significant lack of overlap in the stock timing that I think I can push the events in the direction of more overlap without too much worry of emissions problems.

Stock timing closes the ex valve 13 degrees before TDC. (I say close but MB spec is given at 2mm lift) Opening the valve later (I'm thinking 3-5 degrees) will give a few more degrees of combustion doing work before blowdown helping low end torque a smidge and everyone with a .980 knows it needs all the help there it can get. It will also hold the ex valve open a few degrees longer before closing helping to clear as much spent gas from the cylinder, lessening reversion past the now earlier opening intake valve. The late blowdown would normally cause concern for pumping losses but the 4 valve heads tend to have really good flow coupled with my ex port matching and better flowing muffler should help negate higher RPM pitfalls while still getting the low end torque advantage. I don't have any expectations of any gains due to overlap as I don't think I'll end up with enough to really get much effect from it.

Stock in advanced position (where most driving occurs) the intake valve opens (again 2mm) at 4 degrees after TDC. I want to advance that 6, maybe 8 degrees with the new cam. That will keep the LSA on the tight end (102-104) as well as keep the lobe centerline close to stock. This will close the valve around 10 degrees after BDC. This is 6 degrees later closing than stock and isn't likely to cause a perceptible loss of dynamic compression. Given how much the head is milled it might could stand to lose a bit. Assembled valve clearance may keep me from actually hitting my timing targets but I'll cross that bridge when I get there.

Retarded, the intake cam will open 18 degrees earlier and close 1 degree earlier than stock. The resulting LSA will come in around 111 degrees which by conventional standards is pretty wide but significantly less than the stock 118. This of course is all with the 20 degree advancer installed instead of the 32 degree advancer.

This is where I'm at. Head should be done next week. With the valve job done I can measure for lash caps that will make up the base circle difference. From there its assembly and setup.

duxthe1 · #17 05-22-2017, 08:31 PM

Head work held up. Needs exhaust guides and the only reasonable source is a week out. My wholesaler has to order them from the manufacturer who will ship on Friday. This, after waiting two weeks for my machinist to get to it. The up side is that I can get 12 guides for less than MB wants for one.

97 SL320 · #18 05-23-2017, 04:29 PM

I still vote for leaving the intake valve stems long and grinding the valve faces / seats a bit hard in order to take up the 2 mm gap caused by the cam swap. A small change on the tapered face = larger change in stem height. A spare intake valve might have to be ground extra hard to measure heights and see if this is possible.

Doing this could get you away from lash caps that can escape if the valves float It also allows the lash adjuster ( lifter ) to extend farther in normal operation. If the lash adjuster has a good retention system, lash adjuster pump up distance will be reduced.

duxthe1 · #19 05-23-2017, 07:34 PM

I talked to my machinist about not grinding the stems, but I'm sure I'll still have extra clearance. Once the head is done I'll know more about what I'm working with but I don't think I'll be able to get away from lash caps. My early head has double valve springs and I'm looking to go to the lighter lifters so I'm not really concerned about valve float. I am concerned about having enough valve stem to perch a lash cap on. There is very little valve stem above the valve locks in the retainer. I have to wait another week before I'll have the head back in hand to see where I'm at.

benzevo124 · #20 05-24-2017, 10:49 AM

Quote:

Originally Posted by duxthe1

Head work held up. Needs exhaust guides and the only reasonable source is a week out. My wholesaler has to order them from the manufacturer who will ship on Friday. This, after waiting two weeks for my machinist to get to it. The up side is that I can get 12 guides for less than MB wants for one.

I have 12 bronze guides left over from my AMG head rebuild. Check the part numbers to see if they work with the .980. $20 shipped if you want them.

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duxthe1 · #21 05-24-2017, 01:26 PM

Thanks for the offer. I've already got guides ordered in. Will get them early next week.

benzevo124 · #22 05-24-2017, 01:55 PM

No problem.

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97 SL320 · #23 05-24-2017, 08:22 PM

Given most valve faces are 45* ,a total of 1 mm off the valve and seat would give 2 mm at the stem tip.

I'd measure the height of a fully expanded lash adjuster and then at stock running height. Having a lash adjuster running height slightly tall would be OK, running it a bit too tall could result in a valve tap until they pump back up. ( A stopped engine has some valves under compression so the lash adjuster will bleed down over time, it takes a while for them to pump back up to take out the lash. )

There is a web site called speedtalk.com , very serious engine builder are there and this subject just has to have been covered on a similar engine before.

duxthe1 · #24 05-24-2017, 11:04 PM

All of the talk over there on the subject is related to pushrod V8s. It seems its fairly common in the VW community though actual useful info is uncommon.

My hope after leaving the valves long and adding a lash cap is that it ends up deep in the lifter. Deep enough that the additional lifter clearance is less than the lash cap's skirt depth. I could sleep ok at night in that scenario.

97 SL320 · #25 05-25-2017, 07:26 PM

I've been searching for the Euro guy that used a ex cam in the intake but can't find it. I haven't been able to find it on this site so it may have been on the Turbo Bandit guys site.

I'd also be tempted to mill down the intake side cam pads then line bore to bring the cam closer to the head.

duxthe1 · #26 05-25-2017, 10:06 PM

I did some more measuring today. The lifter I intend to use has 3.1mm plunger travel. Depending on where the valves were originally, it may not be big issue.

I also measured the piston protrusion above the deck, 0.86mm. The head gasket has a 1.76mm compressed thickness. That ends up with a .9mm squish. I'll post chamber volume after I assemble the head.

whipplem104 · #27 05-26-2017, 09:31 AM

To be honest the minimal work on the cams is not worth it. After all that I have done I would not spend any money on this or time again. Unless I was going to go for it all and have a real cam profile made with real lift and depending on the application duration. It just requires thousands upon thousands of dollars to do anything that makes a real difference.

duxthe1 · #28 05-26-2017, 06:43 PM

I'm not expecting to re-invent the wheel but picking up 17 degrees duration on the intake with creative parts swapping while its already apart seems like a worthwhile exercise. As a 20 year M/B tech its a matter of honor that my own personal car performs at least a little better than the average. I am not and I would not spend very much money to pull it off. The cam and advancer are freebies from the parts bin. The head work it needs regardless. I actually enjoy the time spent playing hot rod making and tweaking parts. Reminds me of my youth when I enjoyed wrenching on hot rods, before I lost the hobby to my profession.

97 SL320 · #29 05-26-2017, 06:44 PM

Sometimes the journey is the destination. I don't see our guy spending much $ on this project. A) because has has access to piles of parts and B) based on past projects, he likes to do non standard stuff more or less on the cheap.

I wonder if another brand of buckets could be fit to this head that have taller installed height.

97 SL320 · #30 05-26-2017, 06:45 PM

I typed post 29 before I saw any of post 28.