Doing a top end/upgrade. couple questions, heads, rings and deckheight extremes. Options

[Aaron Cox]

motor ate a head gasket. pulled it apart before it could flame cut a cylinder or head.

so its apart. 71 x 94, with LARGE cam. has mahle euro '8:1 pistons" in it.
deck was setup at .031 but was running a head gasket.

heads have never been decked/surfaced. pulled em and cleaned em, 2 chambers have a sparkplug crack starting - so they need to be welded.

while its apart, i plan to re-ring it, hone the barrels, get the heads done, and???

questions - what rings do you recommend for mahle pistons?
certain rings justify certain hone finishes right?

heads need welding.
valves are sealing great to the seats. guides are good. (motor has 35 k on it since full rebuild.) when the head gets welded, will this require new seats/guides and a resurface?
what is the proper welding setup- my machinist may want to weld em cold, but i was told to pre heat em first - your thoughts?

when reassembling - how tight can i go on deckheight? the euro pistons have a .034" dish to em. should i trim the pistons .034 to make them flat, and trim the cylinders accordingly also?

trying to get as much CR with these 94mm pistons as i can, and running 91 gas.

last question- cam. how does the cam affect deck height? how tight can i go?

going to CC my heads tomorrow - before machining.... what is the range for a stock 2L head? 55-65cc's?

*on reassembly - head gasket will be omitted, and cylinders will be lapped into the head. valves will also be lapped into their seats again.

[Dave_Darling]

Welding the heads is not a simple process; you do have to do pre-heating and so on.

Welding on the heads will make them move around enough that you will need another valve job to make sure the valves and seats are still concentric.

Heads would originally have had "about" 56cc volume, IIRC. But small differences in the volume can have relatively large effects on the CR, so measure measure measure!!

--DD

[Aaron Cox]

Welding the heads is not a simple process; you do have to do pre-heating and so on.

Welding on the heads will make them move around enough that you will need another valve job to make sure the valves and seats are still concentric.

Heads would originally have had "about" 56cc volume, IIRC. But small differences in the volume can have relatively large effects on the CR, so measure measure measure!!

--DD

i pickup the syringe and discs tomorrow..... will measure.

so a valve job would be required again (simple), but the seats would have no risk of getting loose in the pre-heating or welding phase?

[DanT]

If you weld you will need to redo the whole enchilada from what I have read on Jakes site.
Heating and welding can cause problems with the seats.
Cracks means start over from scratch on the heads. (IMG:style_emoticons/default/sad.gif)

[Brando]

questions - what rings do you recommend for mahle pistons?
certain rings justify certain hone finishes right?

Go with a good set of Hastings rings. You can buy them from jake, or ask FAT performance in Santa Ana. You can probably hone the cylinders yourself but if you've got a machinist doing work for you, why not have them do the cylinders for a few pennies more?

heads need welding.
valves are sealing great to the seats. guides are good. (motor has 35 k on it since full rebuild.) when the head gets welded, will this require new seats/guides and a resurface?
what is the proper welding setup- my machinist may want to weld em cold, but i was told to pre heat em first - your thoughts?

As DD said, there's some special procedures for welding aluminum heads, one of which is pre-heating the metal. After that you'll need new seats and probably have the heads flycut and decked to have a true sealing surface.

when reassembling - how tight can i go on deckheight? the euro pistons have a .034" dish to em. should i trim the pistons .034 to make them flat, and trim the cylinders accordingly also?

I believe the lowest you can go with deck height on a mildish cam is about 0.03", maybe 0.025" if you want to be kissing the carbon off of the combustion chamber. But without truing the cylinder seating surface on the case, you'll probably have 0.03" to 0.035" without the gasket.

Are your cylinders domed or dished? lower compression would be dished, higher would be domed (think 944 pistons or CIS pistons for a late 70s 911 engine). You can have them flattened if you wish, but that might take away that little bit of a bump in compression you're wanting.

last question- cam. how does the cam affect deck height? how tight can i go?

Your cam does not affect your deck height per say, but the opposite to a degree. With incredibly low deck height you're limited to cams that don't have extreme lift. Think of it as the piston being closer to the spark plug and valves in the cylinder, then the cam pushes the valve inwards towards the piston. With low lift this is not as much of an issue, but with high lift and the proper amount of duration -- Piston: meet valve, Valve: meet piston. Steel and aluminum don't blend this way.

going to CC my heads tomorrow - before machining.... what is the range for a stock 2L head? 55-65cc's?

Tolerances per the Porsche 914 specifications indicate 56-58ccs per chamber. You can go lower for more compression. Play with a static compression calculator to see what volume combustion chamber would be best for you. Keep in mind, you're taking material away from the heads to lower the chamber volume. You can always subtract, but adding is a bit more difficult (and costly).

Hope that helps a bit, bro. And I should be getting your lapping tool and valve removal tool tomorrow mornin.

[Aaron Cox]

good info brandon, and as i was guessing..

dan - your info sucks (IMG:style_emoticons/default/tongue.gif). bummer on the seats/guides needing to be redone.

deckheight with NO SHIMS under it would be .014.....

jake says he goes around .025-.040.
.030 is cool with me...

ill cc the heads tomorrow. off to the machine shop tomorrow then. i was PRAYING i would have it back together by end of spring break.... need some miracle machining turnaround time (IMG:style_emoticons/default/smile.gif)

off to rimco or Costa Mesa R&D machine tomorrow.....

lets see how much money i have to bleed.

anyone need a chrome rear bumper?

[Brando]

If you got it apart that far bro, find a 78.4mm crank and let 'er fly!!!

Rimco is OK for the price. I'd recommend FAT over them (from my just previous experience). Look at about $200-$300 for the spark plug holes, decking and seats/valve job. You're reusing your valves? If not, start thinkin about $12-$15 a valve if you go SS.

[McMark]

If you have a dish in your pistons your can go lower on the deck height. The dish is going to cause the most problems in getting a higher compression ratio.

[Twystd1]

If you mill the top of the pistons, and cut the barrell down to match heights.
How much space between the top of the piston and top of the first ring?
That can be an issue in itself.
John will have the answers using some math and some measuring tools......
of what will work as far as deck height and interference problems.

I have much tighter decks on a 103 with flycut pistons on one engine... No problems.

I don't know stock piston heights at all....

AA... shoot over to STF and do a search on deck height + stock pistons. Jake and others have written profusely about this subject using stock pistons. I think you will find ALL the data you need there.

Make some time to go over to Brians shop where we can blast your cap....

And we can glass bead your heads at the same time..

NOTE. Buy new exhaust studs before ya put this bad boy back together again. Welding heads can do some weird shit to heads.

C

See ya tomorrow if you are coming my way.....

C

[Bleyseng]

yep, buy the exhaust and rocker studs from Jake as those don't breaky. Cams do have a affect on dynamic compression vs static compression.

[Aaron Cox]

but any cam should clear a .030 deck right?

[Aaron Cox]

dropped the heads off at the machinist to get...
-cracks welded up
-seats
-guides
-valve job
-might go one size up on the exhaust valve
- rings
-hone
-valve tips resurfaced

[craig downs]

Hey Clayton from the top of the piston down to the first ring it measured .300".
So if you mill the top flat it should measure .269. But he needs to know how many
cc his heads have before he can figure what size deck he needs

[Aaron Cox]

hoping for around a 54cc head.....

[Matt Romanowski]

As for clearance from valves to pistons, do what everyone *should* do (not just what people say they measured). Put some clay on the piston, assembly, turn over, disassemble, cut clay, measure. That is the only way you know what kind of clearance there is.

Also, I believe all the dished pistons are standard compression, with the Euros being flat topped and higher compression (at least all the one's I've seen). Fly cutting the entire top of the piston flat is probably a bad idea.....

[Aaron Cox]

As for clearance from valves to pistons, do what everyone *should* do (not just what people say they measured). Put some clay on the piston, assembly, turn over, disassemble, cut clay, measure. That is the only way you know what kind of clearance there is.

Also, I believe all the dished pistons are standard compression, with the Euros being flat topped and higher compression (at least all the one's I've seen). Fly cutting the entire top of the piston flat is probably a bad idea.....

clay- good idea. will do that on mockup/assembly. has some pretty beefy springs in it too. ill see what their spring rate is.

motor spun to 6200 rpm fine before we tore it down. valves didnt float... but i will verify their springrates again. (rest of valvetrain is manton cromo pushrods, 911 swivel feet and 1.7 rockers - soild spacers... johnston solid lifters.)

AA

[Twystd1]

I am just wondering if .269 is safe for the top ring.

Ring flutter can kill the rings in no time flat if there isn't enough clearance.

I need to look in my books and call a few guys to make sure what will work.

The pistons I use have lateral gas ports. With that setup. I can go very tight and THIN clearances.

I think the Mahles have no gas ports... Correct?

Clayton

[Aaron Cox]

any comments on 'grant' rings?

[craig downs]

His Mahles don't have gas ports

[Twystd1]

Then he might not want to cut the pistons if he is looking for longevity.

If he is racing... No problem.

And Aarons engine has seen way over 6200 RPM...
Every time I drove it. (IMG:style_emoticons/default/chair.gif) (IMG:style_emoticons/default/WTF.gif) (IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/alfred.gif)

Once the top AND bottoms of the cylinders are flat and coherant to each other.
And the combustion chamber sealing area is decked FLAT.
Then he will need to mock it up again and see what the clearances are. At that point. He can look at shaving the pistons... And the block side of the barrels.
Until then.. it would be guessing on how much to remove from the cylinders or the pistons.

Clayton