Block Decking Questions

[bullet19]

:p

On a 2.4 200, Besides the D-port and enlarging the fingerport holes on the piston, will enlarging the windows in the skirt help or hurt anything??
I have heard about modifying the rod slot, are there drawings/pics somewhere of this correctly done??
I am about thru amassing parts and ready to get the grinder out:eek:
I guess I will be giving my local machine shop some money too!!
T-rex has enlightened me on some things to do to my lil 2.4. soooo all the locals might get a lil suprise come spring :D
Thanks
Bryan

[Ryan140]

I wouldnt cut any more than the transfer and boost ports on a cast piston if I were you. I had the same idea before everyone showed me pics of what happens if you do. Rods slots get conflicting opinions around here. If you do a search under my name you will find a post from about a year ago which had like 25 responses. The only thing everyone seems to agree on is adding compression, removing casting boogers, opening the bottom of the block, rubber reed blocks, and opening pistons. I do have a question for everyone though. What is the advantage of decking a block and pistons as opposed to cuting a 10* bevel around the edge of the piston. This would intern do the same thing wouldnt it? Raise timing and change intake duration. I am doing this mod to my chrome bore project motor this winter. I plan on cutting it about .050. This way if I dont like it I can still go back to what I had. (just need another set of pistons). One thing I would say that you could do that I didnt see anyone else post is to remove your exaust adaper and open the top to the block, the bottom to the tuner, and the 2 pieces to each other. I pinned mine to do this other wise everytime you bolt it togeter it doesnt match up. Also some people (me included) like to have .050 shaved off the front of the front half to increase crank case pressure and speed up the charge, some say it doesnt work though.

[STVRacing]

From my experience decking the block is safer. You will get both sides the exact same height if done by a professional. Chamfering the pistons does the same thing but the only problem with that is there really isnt alot of meat now between the top of the piston and the ring groove. I would be really concerned that over time if its a stock piston it will collapse.Either way you go you are still raising the exhaust port height. My 2 cents. Steve

[steve]

When you deck a block, you do absolutely nothing to port timing unless you cut the pistons as well. You reduce squish area but not port timing. You are trying to change port timing to make more hp and move the powerband higher, correct? Then the chamfering would be a much easier thing to try. Remember, the piston cools in the squish band at TDC so too shallow of a chamfer will affect squish area and cooling as well.

Chamfering .050 removes less material then decking and cutting the pistons. Which would make it a safer bet . Though .050 isn't much. Either should work fine. Chamfering won't actually change the port timing as much as if you cut the pistons flat because you are not opening the port fully with a chamfer. Cutting the piston and decking you would be.

Did you mention a light flywheel? And yes cut the .050 off the front 1/2. Widen the slots , but don't do those huge angle rod slots or you'll lose bottom. Run the 5250 rods and 9 rings on the crank. My 4 cents.

[STVRacing]

To think ll this time I thought I knew what I was talking about and then we get a GENIOUS who comes along and says that Im not raising my port height. I guess all my experience by doing this is rendered useless then.:eek: Yes decking the block DOES raise the port height!

[steve]

Sorry. Try door # 2 . Think of it this way. Port timing from crank to piston to wall . No change. Squish is changed. Compression is changed. Not Port timing. Try it with a degree wheel if you are really not sure. You have to cut the piston to change port timing. ;)
But, you did get part of it right ...Genius. :p

Its only the 17th so I'm keeping the can closed. :eek:

[Dave S]

Deckin the block gives you a smaller reading on the mike when checkin the port hight, but you didn't change the timming. Unless you cut the top of the slug. I think cutting a radius at the exhaust side of slug, changes the ex only giving top end. Also dosn't weekin the pisten. The ring is sheilded by more piston that way.

[Raceman]

MercThunder, if you think decking the block raises the port height, you need to go back to the two stroke 101 course. It does raise the height in relation to the top of the block, but does ABSOLUTELY NOTHING for port timing, which is all we're concerned with. Port timing is simply the number of degrees of crankshaft rotation from TDC that the port begins to open. It doesn't matter if the deck height above the piston is .0000 inches or 10 feet, the port timing is the same. Cutting block deck height is simply another way to modify compression, or fix an unstraight surface. Cutting the deck surface does give some other options such as combustion chamber squish design while maintaining or increasing compression, and of course if the tops of the pistons are chamfered, either 360º or just in the ports as we used to do it, which does in itself effectively raise port timing, block decking may be useful for optimum combustion chamber design. Think about it, it's really common sense.

[Raceman]

Dave, I guess we were typing at the same time. I used to cut a chamfer across the exhaust port opening width of the piston top only, but they can be cut thin enough that the ring will snatch the edge off the piston there. I can't remember how much we whacked em, but may still have one or two. I do remember my partner's motor having a failure from losing the edge above the ring, but he was an "if a little bit is good a lot is better" type modifier, so he may have had em REAL thin there.

[Dave S]

You just type faster, can spell better and hit the submit button faster.:D You win.

[Russ]

Milling the front half will increase crankcase compression, the real effective gains to be expected are minimal. The fun part is trying to measure the incr in case compression! Fly cutting the piston top is a standard operation depending on what your trying to do. It's a neccessity if the block has been decked a fair amount. Doing a chamfer cut on the piston across the exhaust port is a fair game practice too. Done on mine and still have it in place. It's a cheap way of changing your port timing. Can swap in and out different pistons with or without the chamfers depending on what your after.

[bullet19]

Could someone maybe show a pic or diagram of a chamfer @ the exhaust port:)
Bryan

[Russ]

the EXH port, on the piston where it meets the EXH port. It's more like a relief cut into the piston. I can post a pic of an old one, if your really interested?

[Ryan140]

Russ I have most all of my front halfs decked. I put the bevel all the way around the piston for a few reasons. One is the port heights everyone says to be at for a strong lake motor are higher than stock on both intake and exaust not just exaust. Plus the piston is open longer on the bottom end changing the intake duration which some say is good for some midrange power. Also I couldnt figure out a way to notch just part of the piston and get them all the exact same. Some made the comment that you should deck the block cause everone would be the same. I got all of mine the same with no trouble. Im not saying this will work or wont, Im saying this is what Im trying on my winter project. If it doesnt then all I have wasted is time and pistons. If you deck a block you cant go back.

[VectorPat]

I would like to see a picture if you got one.........

[bullet19]

The pic would be worth....A Thousand Words!!!;) :) :) :p
Thanks
Bryan

[Raceman]

If Russ doesn't post one tomorrow I'll try to dig one of mine out and shoot it.

[Russ]

Quit steelin my thunder!!! LOL (kidding) I can't post one from work, but will when I get home later, and Raceman, go for it if you got one ready. Ryan, yes, fly cutting the piston as you state will change your time area for sure and can have favorable effect depending on what your going for. It doesn't take much of a timing change to see quite a difference in performance. I remember an F1 engine showing up that was bought off the trailer or whoever the "F1 motor Kaizer" is for all of Europe that was brand new. Before it was reworked it was mounted on the dyno to run up a baseline for it. When we were through and corrected the numbers, we looked at each other going "holy sh%t!" did we do this right? Did it again...same result. This engine was stronger in every important aspect than any other UIM F1 motor that came thru the shop. Needless to say we poured over this one to find out what was different. We found it. This engine appeared to have a manufacturing error made when inserting the sleeves on all 6 holes. The port timing across the board was 1.0mm higher than top of the tolerance spec. These sleeves hadn't been fully seated to the floor, they were all up a millimeter higher than they should. :-)

[Raceman]

"and Raceman, go for it if you got one ready."

Hahaha, you haven't seen my shop. I don't know if they are, or where they are. If you've got em ain't any sense in me goin' scavenger huntin'. Last time I went that far in the back there was a mad as hell momma possum with about a half dozen babies.

I'm surprised that a factory Merc F1 motor would have room for another mm of port height. I'd have thought they'd have it at the point that it would start falling off with more port timing.

[Russ]

was quite a little surprise! A very nice one we learned something from that money/time didn't need to be committed on to get an answer to.

[Russ]

I don't post pics much, maybe once. Hope she comes out.

Dammit, no it didn't...try again later.

[Russ]

will probably be strike 2... HA! look at that...I did it!

[Rusrog]

You ARE smarter than you look...

hehehehehe

Talk to ya later,

Russ

[Russ]

Russ! You can subtract one of those steak dinners I owe you! Raceman, from your comment above, if I understand it correctly...I don't think Mercury Racing has exhausted the full potential of the F1 engine/Drag. I believe they feel they are close, but have some emergency reserves ready, if ever needed. We won't see those however. They will only draw on those if they see a real threat to them in F1. They put out what they know will compete, and almost more importantly will LIVE through a race. They protect themselves to a degree to make sure they minimize any black eyes coming their way. They want their products to look good out there and if people see a bunch of broken Mercurys happening at every race...would make one wonder. Anyways..going off in a different direction now...see ya.

[Raceman]

Russ, your piston looks a lot neater than mine did. I did em with a disk sander (yeah, yeah, I know) and had em tapered back farther. We usta' scribe the width of the exhaust port while the pistons were still in the motor, then tear it down and whack em. Back yard engineering at it's finest. Hell, back then an electric disc sander was a sophisticated piece of equipment to me, and I was at least as good with it as T Rex is with the hammer and chisel he uses now.

[KMA1/4master]

well I used a lathe, a feeler guage ,an old radiator clamp,and a die grinder with a sanding roll.and after reading all this im thinking of doing it again

[Russ]

A Bridgeport and rotary table will make anything look good. Disc sander? lol. I heard a story about (may have been Bill Seebold) that was at a race and badly needed more compression. No machine shops anywhere around...there was a cruise ship in dock nearby...the team descended upon the ship/crew and found out they had a large table disc grinder on board. Said they were welcome to use it...and so they did...was pretty rough, but guess what...worked just great! and off they went...

[rgsauger]

will probably be strike 2... HA! look at that...I did it!

Dang this is interesting! Never seen this before.