help too much lift

[marv914]

help i have too much lift. I am rebuilding a 1.8, It now has flat top pistons and a web cam that lifts to .435. I also have 1.48 ratio roker arms. The valves are touching the pistons. How much room is there and how many spacers or what size push rods should i use to correct thei problem.


Thanks Marv

[Special K]

Just bumping you up to the front. I personally don't have a clue, but there's quite a few here (Jake) that can probably answer your question.

[cnavarro]

There have been some threads discussing pushrod geometry on the 914club website. You might want to start there. If you still need more clearance, you'll need to add valve pockets, depth depending on total clearance required and dome thickness. Also, if you run those ratio rockers, you'll want to add some oil squirters to the valve covers to help with valve guide lubrication. i speak from experience here after wiping out a valve guide from lack of lubrication with the ratio rockers, since they are non-oiling.

Charles Navarro
LN Engineering
http://www.LNengineering.com
Aircooled Precision Performance

[mike mueller]

It depends on where you want to put the spacers???

Are you happy with the compression??

Have you measured everything to figure out the compression??

How much interferance do you have between the pistons and the valves?

Like Charles mentioned, you'll have to mill the top of the pistons to make reliefs. You can use clay on top of the pistons to get the location and angle needed. You need to figure out the depth and add a safety factor in case you float the valves by accident. You will also have to make sure you do not weaken the piston by adding the reliefs.



You will also need to get cut-to-legth push rods (Pelican might have them, if not aircooled.net is where I bought mine from)
There is no exact number for the length, you need to buy or make an adjustable pushrod for testing.

In simple terms, the length of the pushrods are correct when the tip of the roller rides in the center of the valve stem at maximum lift (I'm pretty sure, but you might want to double check)...too short or too long and you will not achieve full lift

Nothing personal, but do you have any books or guides to help you? It sounds like you are throwing together an engine without some basic background experiance with motors.

If you've read this far without getting pissed off at me , I'd recommend the following:

Measure the cc of the heads and figure out what your compression is going to be.

If too high, you can add spacers between the cylinders and the case, if you get lucky, this "might" also solve your piston/valve issues.

If compression is "just right", you'll have to add the reliefs in the pistons (you still might with the spacers, just not as much)

When you are happy with the compression, then tackle the pushrods.

I had a set of the Pauter roller rocker arms and sold them, too much worry for a street/daily driver due to the oiling issues.

[Dave at Pelican Parts]

A few minor quibbles with Mike's note--

First, adding valve pockets in the cylinder tops will also change your compression. Don't forget to add the volume of those pockets to the "fixed volume" figure when you're doing your calculations.

Second, when adjusting the pushrod lengths and rocker stand shims, you are shooting for having the adjuster parallel to the valve stem when the valve is at half-lift. Do a search over on http://www.shoptalkforums.com for "valve train geometry", and I think you'll come up with some good info.

Otherwise, "What he said."

--DD

[norustscott]

Why ratio rockers with that cam ? Is the lift, .435, measured @ the valve or is this the WEB cam data? With your ratio rocker arms you would get something like .640" of lift...seems like too much for a streetable engine...

My experience with cam/rockers has been to tune duration with the cam and coordinate lift with ratio rockers. This will extend valve train life by allowing you to slow down the lifter speed.

Consider going with 1.25 rockers...? Or even 1:1.

[cnavarro]

The type 4 engine came with 1.3:1 rockers stock; the only available rockers are 1.48/1.51:1 rockers from Pauter.

[norustscott]

Looking back it appears I forgot to take my Type 1 hat off...8)

[cnavarro]

Happens to the best of us :-)

Charles Navarro
LN Engineering
http://www.LNengineering.com
Aircooled Precision Performance