logray

I got my upgraded case halves back from LNE on Friday. One of the work performed was a surface grind.



Question is, should I leave the heads alone or have them ground as well? Both heads are currently at 5.6080" deep. Would it hurt if a few thousandths were taken off of each head to get a clean mating surface? And require minimum surface unevenness after machining of 1 thousandth or less?

nick49

The finish on your heads is such that it will seal perfectly as is, providing there is no warpage. You can take them to a well equipped automotive machine shop and have them checked out for flatness. They will advise you. This is something either you need or you don't. On a ohc motor if the heads are moved closer to the deck the valve timing will be off which on some motors can be compensated with adjustable cam drive sprockets. A couple of thou is no big deal, but sometimes heads are milled .025" to .040", then piston to valve clearance should be checked as well. Bottom line: do only what is needed, then make necessary allowances. GL!

Dharn55

Remember that when new cylinders are inserted he height of the liners has to match the deck of the cases, so in this case some machining is pretty much mandatory. Per nick49's comments, even this could effect the valve clearance, etc. but I am sure that LNE has the experience to do this. Checking the heads for warpage is probably not a bad idea. Also remember that head gasket are used and the tolerance of these is certainly not within .001".

When I was doing my engine repair for a cracked head I considered buying a used head (could ot find one without cracks) or a new head ($2,800++). I discussed this with Jake Raby and he noted how important is was to match the volume of the heads. So if you take some material off one head you may need to do it to both. Not sure how much a few .001" would effect this though.

logray

Thanks for the tips guys, will certainly be dropping those heads off to have them checked for warping and evenness.

I was thinking about many of these things before hand so it's good to know I'm on the right wavelength.

Per my pics, there seems to be a pretty noticable imprint left over from the head gasket/cylinders on head #1, but not as dramatic on head #2. Yet on the heads I see that come back from various sources, they have a clean surface on them - devoid of any gasket marks. This is sorta was sparked this question.

I had it in my mind already that heads matching as close as possible in height being very critical.

And as for the deck height, I am guessing whatever material LNE removed will increase the CR and reduce valve and spark clearance, unless the matching JE pistons are also a little shorter? Don't think so though, not sure.

Anyhow, I'm wondering how much leeway is there for a CR change if said material is gone from both case and head. Example a few .001"s taken away from the case, and then a few .001"s from the heads, if I need to worry about that (in the form of a custom shim/head gasket or new heads). Of course if we are talking about 0.1'ths or 0.01'ths different story I assume.

nick49

Hope this will help

Generally a rebuilt head will either be glass beaded or kissed by a resurfacing grinder. This doesn't remove enough material to raise the CR or be of any concern. The clean, as new surface looks good for the customer, but the motor doesn't really care if there are imprints or stains from the previous gasket, so long as the surface is straight within spec.

Any deck material removed, I'm sure was just kissed and won't make any difference anywhere except to insure a good seal. I'm guessing .030" to .035" taken off the heads may give you a quarter point increase in CR. Not enough to justify having to make valve pocket depth checks and re-degreeing your cams, or at least checking the altered specs. Often if a head's out more than .010"-.020" it may be questionable if it can be saved and used for a replacement. These specs will vary widely by motor type so it's best to check factory tolerences for each head.

speed rII

For the ohc engines, it's highly suggested to do nothing for the head surface, if it's not needed.

Camshaft bearing line will go off if you surfacegrind the head's wrong way.

To me, your head's look's like they are ready to go

speed rII

also, if the deckhight and the heads are surfacegrinded, your stock timing marks are off. And you need to use dial indicator and degree wheel to set up your timing.

wyovino

I really envy guys who can tackle jobs like this. I feel self-satisfied after changing my air filter. You guys are in a whole different ballpark, but I love following your threads.

logray

Thanks again everyone for the input.

I've got a couple really GOOD examples to work from here.

The first is from byprodriver's rebuild, which is identical to what I'm doing. He quotes a stock CR with the LNE 3.6 rebore/JE pistons (and deck surface grind), and had his heads worked on (guessing they were "kissed" with the surface grinder). He also used the factory cam method to set timing and installed the cams straight up. SO... I am guessing there was not enough material removed on either side to worry about the CR or cam timing changing signifigantly enough to cause concern. I'm supposing the chain tensioners soak up some of those indifferences. Is there a small amount of power lost by not using a degree wheel and dial indicator? Perhaps, but probably pretty insignifigant for the daily driver.

In the second example, we have crazy Jake rebuilding a very custom M96 engine. In this particular case, most certainly the engine is running an insanely high CR and he even threw out the custom head gasket shims! Of course he used split overlap, degree wheel, dial indicator, etc to alter cam timing from stock (he also reground cams). Is the car still running? Probably without a doubt! :-)

example 1 from: https://rennlist.com/forums/996-foru...rebuild-2.html



example 2 from: http://www.flat6innovations.com/engine-assembly



"After tightening a few fasteners and attaching the cylinder 1-3 rods and rod caps onto the crankshaft assembly I roll the crankcase half over with the crank carrier combo installed to verify and record our cylinder 1-3 deck heights. With the LN procedures the case decks are surface ground and this means excellent accuracy, all our deck heights were within .0015 of each other, which makes for even combustion balance and a very smooth running engine!"



"Custom MLS head gasket shim used for adjusting and fine tuning of compression ratio with our larger bores and added stroke. We chose not to install these in this engine ecause we wanted an insanely high CR and very tight deck for this test engine, to push the limits. We believe in R&D - "Risk and Development"."

nick49

Sounds like you're good to go.

Tensioners only remove slack on the back side of the cam chain if that makes any sence. In other words, the chain may run in a guide but is kept tight between the intermediate shaft and the cam (s) so timing always remains constant.

A degree wheel and dial is used only to verify timing and establish it when using other than stock grinds. You need to know the lobe center specs, open and close degrees and at what lift, also a way to make adjustments as most cam drive sprockets are non adjustable. If the sprockets are keyed, stepped ones may be available or multi keywayed sprockets or gears. Sometimes mounting bolt holes are elongated to make them adjustable. When getting involved with all this, you can choose the motor characteristics you desire and add more torque in the rpm range desired. With a dohc you can increase or decrease valve overlap as well altering cylinder fill vs rpm. This suff is where the fun begins building race motors, and even funner if you are the test pilot.

Flat6 Innovations

You just spent a significant amount of money on the cylinder upgrades. Have those heads worked, have them fully worked with all new quality hardware (Not OE!) and the head surface MUST be decked. We typically find the head deck to be .0015 to .003 uneven on every engine. We firsat straighten the head and then deck the head using a CBM procedure.

Remember, these are the things that we see failure wise from heads today:
-Dropped valve seats, especially in later 3.4 engines and 3.6 engines through 2003. We have found as little as .0005 interference fit on these valve seats.

-Broken valve springs, I'd never reuse a set on an engine with this much money expended on cylinder upgrades

-Worn valve guides, especially on the intake side of things

- Bad valve stem seals- Makes for smokey start ups and oil consumption

- Cracks- We had an engine come in with a rod failure, when we tore into it we found a cracked head that had not intermixed as of yet.

Approach with care and a mindset of doing it all the way or not at all. The quickest way to waste thousands is by trying to save a few hundred. I am not promoting the heads being sent to us; primarily because we don't have the time to repair them, and because our level of preparation for them costs 3K.. But someone certainly should give them the time they demand, else you are leaving an open wound waiting to be infected. Been there, done that and won't make that mistake again.

The first rule in enine assembly is to never assume anything; the second is to quantify everything. Apply this to the CR and deck height measurements, ring gaps, ring positioning and every single part of the engine.

Never say never when practicing medicine or mechanics~

speed rII

And now that I have thought this one again, this is just bs
Sorry!

Of course the stock marks are ok, the cam sprocket will compensate the diffrence in height.

The cam timing will be the same, when it's adjusted per instructions.

Jake, do you have link for this CBM procedure?

Flat6 Innovations

This isn't a conventional engine in regard to cam timing difficulty when assembling after decks have been altered. Use the cam timing tools as standard and you will experience no ill effects during assembly and cam timing procedures. I have only had to utilize the split overlap cam timing procedure once during my years of developing the M96 platform.
The CBM procedure requires a CBM machine to utilize.

logray

Does the CBM machine provide a cut with required RA for the MLS gasket? Or do you have to hone & polish it afterwards?

I am guessing a very low roughness here, maybe less than 15 for a good seal?

Flat6 Innovations

Properly configured CBM machines provide an RA optimum for the MLS gasket.
After we cut heads they are washed in an ultrasonic bath then finally assembled and fitted to the engine.