David Floyd

Is this normal or time for a new cam, wear spots on all lobes in the same left side location and on both sides of the high point ??

<img src="http://boards.rennlist.com/upload/Mvc-006s.jpg" alt=" - " />

TonyG

Is it a stock cam?

Also... could you post a better picture. A little more in focus would help.

*eurospeed951*

so why is the head off?

Danno

Those two triagular wear spots on the sides aren't really wear spots. They're just low spots on the lobe that didn't touch the lifters. This is actually not unusual with normal cam-wear; we just haven't seen a whole lot of worn cams.

David Floyd

Yes, stock cam, sorry for the bad pic.

Head is off to have some valve seals replaced.

Thanks Danno, this cam will go back in.

*eurospeed951*

what head gasket will you use when you put it back on? Are you going to try the block brace?

TonyG

What is a "block brace"????

David Floyd

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> what head gasket will you use when you put it back on? Are you going to try the block brace?

</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I have one of the Guru headgaskets, Danno explained to me that the block brace would take some machining to install, not something we can just hammer in place, so I'm not using one.

Tony, the Guru blockbrace is a plate that is placed around all of the cylinders for extra support.

TonyG

David Floyd

Ahhh

All other engine builders call this a "girdle". It's very common, with open deck blocks, to machine one, weld it in, then machine the top of the block flat again.

Also, it's common to use concrete in in the water jacket as well to "stiffen up" the cylinders.

The two steps above usually, from what I've seen, go hand-in-hand.

This process requires a LOT of machine work to do it correctly.

It's not necessary for a stock bore setup. But when you sleeve a block, the sleeves have a tendancy to move around. The girdle will fix that.

Jeff Lamb

"Deck plate" is yet another term used to describe the block brace or girdle that David and Tony wrote about.

Jeff

Danno

For some pictures of a custom hand-made block-brace, check out this site:

<a href="http://www.928sg.com/block.htm" target="_blank">http://www.928sg.com/block.htm</a>

We were trying to develop a press-fit hammer-installed plate like they have for the Hondas. However, due to the casting flashes and production variations, this wasn't possible without moving the tops of the cylinders around during the installation process.

The plate we came up with was similar to the 928 one shown, except it is more rectangular with straight sides. You then machine down the triangular protrusions that include the holes for the head-studs. This gives your block more uniformity with straight sides. The plate then sits on top of the lowered triangular protrusions for vertical stability and holds onto the cylinder tops on the inside. Then boring to re-center the holes and sleeving as usual would be the final step.

If you are going to the extreme of building a big-bore engine, I'd start with a 3.0L block and not mess with trying to modify a 2.5L block for increased power-handling. Got a good look at Jeff's block at the machine-shop and the modifications Porsche made in going to the 3.0L block can't be easily replicated on a 2.5L block.

rage2

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by TonyG:
<strong>All other engine builders call this a "girdle". It's very common, with open deck blocks, to machine one, weld it in, then machine the top of the block flat again.

Also, it's common to use concrete in in the water jacket as well to "stiffen up" the cylinders.

The two steps above usually, from what I've seen, go hand-in-hand.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">With the engine concrete, it should already reduce cylinder/sleeve movement significantly. Coupled with a metal headgasket with an o-ring holding it tight, it should provide for a very strong block without the extensive work involved in a custom block brace. That's the theory anyways .

David Floyd

Can the block be grouted while in the car, tilted ? not going to pull the engine just for this but might do it if it can be done in the car

Danno

"Can the block be grouted while in the car, tilted ?"

Nope, the lower water-pump passage is exposed and you'll grout your water-pump solid. You need to mask off the water-passages in the front of the block so they don't get filled. Then grout the 2.5L block to reduce the cylinder heights by 1/2 (ends up the same as 3.0L blocks).

Perry 951

Also, to head back to the cam question, the lobes are tapered so it will spin the lifter in it's bore. This reduces wear on the lifter top and sides, and also on the cam.

Every 944 cam I have seen has a portion of the cam lobes that have no wear on them. 100% normal.