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Posted by: rtalich Oct 14 2006, 10:09 AM

Can anyone tell me if these heads have been modified and/or why they have a little 'step' bored into them? The first picture shows a 'normal' head. Notice the flat surface shown circled.


These next two pictures are the heads in question. Have these been machined/modified in any way? If so, why?




Thanks,
Rob

Posted by: Bleyseng Oct 14 2006, 10:40 AM

Looks like a piece of metal was loose in that one head.

They were "step cut" for improved head sealing I think.....gotta watch your deck ht when that is done!

Posted by: JPB Oct 14 2006, 11:18 AM

The one middle picture looks like they have cracks at the plug holes going in opposite directions but don't seem to be bad enogh to fix unless you want them perfect.

Nice and clean though and wondering about the combustion chamber size of the cut one and if it would increase the compresion slightly if they are smaller? Are you ballancing these heads yourself?

Posted by: rhodyguy Oct 14 2006, 11:32 AM

i think *other* head people do the same cut. "quench area improvement"?. i can never keep it all straight.

k

Posted by: JPB Oct 14 2006, 11:37 AM

Ahhh, I zee.

Posted by: rhodyguy Oct 14 2006, 12:10 PM

geoff, do you mean in the top picture with the valves? aside from the small cracks, these valveless ones are nice heads. nwcr wants to remove the *shoulder* area (what ever that means). that's why i suggested rob start a thread about them.

k

Posted by: sixnotfour Oct 14 2006, 12:28 PM

Is it possible it is a later revision head that doesnt require the sealing ring? for deck heigth?

the first head ,flat would require sealing ring or if left out thicker base shim? for deck heigth ?


I cleaned the heads for Kevin and they didnt appear to be machined .

CC em and see.

Why cut more than you need to ?

AsK Len or Jake before you cut em.

Just thinking out loud wiating for a 12 year old birthday party to start .

Posted by: Bleyseng Oct 14 2006, 12:57 PM

first of all I wouldnt have Jerry at NWCR work on ANY 914 2.0L heads.....

send them to Len for a quality repair.


they will be trash if they go to Jerry IMHO due to his seat install method.

In this picture there are small dimples that look like a small chunk bounced around in there where the red is circled.
I have only seen the "step cut" once and that was to help seal the head to the cylinder...otherwise I don't know.




Attached image(s)

Posted by: rhodyguy Oct 14 2006, 01:18 PM

that's not one of my exes, or robs newies pictured in that shot.

k

Posted by: Bleyseng Oct 14 2006, 01:27 PM

QUOTE(rhodyguy @ Oct 14 2006, 11:10 AM)

Posted by: messix Oct 14 2006, 02:02 PM

if you use them you should measure the piston height at tdc, and the 'step' of the head to make sure that the piston and head don't make contact.

cc'ing the tdc of the piston/ cylinder and the head [you will have to find a way to fill or subtract the volume of the grove for the cylinders] to calculate the comression ratio. this is important! those heads might have been used on a high compression engine [11-13 to 1] bad for the street!

Posted by: rhodyguy Oct 14 2006, 02:09 PM

rob, give me a call when it's convenient.

k

Posted by: sixnotfour Oct 14 2006, 02:52 PM

Posted by: rtalich Oct 16 2006, 07:37 AM

Len and/or Jake...? Need your opinion please.

Thanks,
Rob

Posted by: rhodyguy Oct 16 2006, 07:53 AM

rob's heads were NOT used on a high comp engine. i can assure you of that.

k

Posted by: Bleyseng Oct 16 2006, 08:42 AM

Heck, for all I know those could be virgin heads that haven't been flycut at all. I can't remember what the only virgin set I have had looked like.

flycut head


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Posted by: davep Oct 16 2006, 10:03 AM

Len Hoffman is member 'HAM Inc'
You may want to email him a link to this thread to get his attention.
He is busy doing a lot of heads for us right now, so his online time is very limited.

BTW, Jake has the archives of the 4th Dimension radio files. Anyone rebuilding an engine should download these 'broadcasts'. They are truly a wealth of information.
I was part way through doing my own heads, ready to install new guides when I decided to send one set to Len. The other set will wait until I decide what kind of an engine to build. I could not see any cracks in my 4 2.0 heads, but I'll wait for the masters prognosis.

Posted by: HAM Inc Oct 16 2006, 12:19 PM

Rob the head with the step has been flycut. Stepcuts were never std with any O.E. T4.
I am a big fan of the step cut. The biggest reason being that more material is left in the head in the weakest areas of the chambers: 1) beneath the ex. studs 2) on the side plug heads (1.7 and especially 1.8's) the area closest to the spark plug. By cutting a step you increase compression with out removing as much material from the head. The head seal seems to hold up better over time with a step as well.
If you have a .75mm (.030") step in the head you need a .25mm (.010") deck ht in the cylinder, for a total deck ht of 1mm. The deck ht. volume in the cylinder and the head can be calculated. A 1mm total deck ht in a 94mm bore will be 6.94cc's a 96mm bore will be 7.24cc's.
The heads in the pictures have not been cut too deep as the top shoulder has not been cut to prevent cylinder fin interference. The heads will need new seats and some crack repair to be made reliable.

I do offer a 10% labor discount to all 914 club members.

Posted by: anthony Oct 16 2006, 02:06 PM

QUOTE(HAM Inc @ Oct 16 2006, 11:19 AM)

Posted by: sixnotfour Oct 16 2006, 05:25 PM

HAM Inc
Thanks for clearing it up

Posted by: rdauenhauer Oct 16 2006, 06:25 PM

You learn something new every day on this board.

Posted by: rhodyguy Oct 16 2006, 07:46 PM

for len's reference. the heads that are in ? are the ones without the valves. i can see where 2 sets of heads could create some confusion.

k

Posted by: Bleyseng Oct 16 2006, 07:52 PM

like I said...."step cut"...


don't mind me, I don't ever know what the hell I am talking about....


Good to hear it from the "Head dude" Len..

hopefully, Rob will be sending these to Len for a rebuild.

Posted by: maf914 Oct 17 2006, 11:38 AM

QUOTE(Bleyseng @ Oct 16 2006, 05:52 PM)

like I said...."step cut"...


don't mind me, I don't ever know what the hell I am talking about....


Good to hear it from the "Head dude" Len..

Posted by: Jake Raby Oct 17 2006, 12:06 PM

I prefer step cut heads, all of my engines use them. The step cut has proven to be an effective means of reducing head leakage for engines that will see high mileage...

The benefits of a step cut will be gone over October 27th in the first of a 2 part 4th Dimension Radio series on cylinder heads. Len will be our guest and you do NJOT want to miss these shows!

Posted by: Gint Oct 17 2006, 05:35 PM

QUOTE(HAM Inc @ Oct 16 2006, 12:19 PM)

Posted by: orange914 Oct 17 2007, 09:39 PM

QUOTE(rhodyguy @ Oct 14 2006, 10:32 AM)