Just to share some more information we found on the EVO 8 head. The camshaft housing dimensions are all over the place. Be careful when installing cams into the housings and how they are tightened, the lack of mass, and the quality of the aluminum cap that hold the cams in can get distorted easily. And it seems to be quite easy to end up with housing dimensions that are not only too large, but not round and can bind up the cam. Here are some pics of a head we just repaired by first measuring the cam housings, clipping the caps, and re honing the housings on both intake and exhaust to proper clearance.

WHat can happen in this case is that the volume of oil can bleed off around the cam bearings, starving the lifter valley of oil, leading to a lifter noise, collapsed lifter, and inadequate lubrication and oil pressure.

The difference once the head was rehoned was unbeleivable. The cams rotate with ease in their housings and do not bind up at all as they often do on the stock head. Oil pressure was stable and no lifter noise.

 

here is a shot of one of the cam saddles after honing

 

you can see the cross hatch patterm from the honing bar showing full contact %100 around the housing. What you cannot see from the picture but I will tell you is that the housing is round, and at a size to yield the proper cam to housing clearance.

 

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what's the cost of getting a head blueprinted? and are the variances greater than you see in other manufacturers engines?
i enjoy your posts, information and display of excellent work!

 

Im not second guessing your expertise, but it seems to me that you have found the EVO engine to be completely "Out of spec". This engine is the same engine that produces countless 330+ dyno sheets, and easily. Every post is about how awfull this engine specs out, yet this engine can and will handle/produce more hp per liter than just about any mass produced engine out there, stock.

 

That is just a testimonial to the engine. I am not talking about horsepower, I am talking about tolerances- you guys need to decide if you think that one relates to the other. This kind of work is not for everyone, this is time consuming, often expensive processes that many people look at and ask- "why bother? My car dynoes at such and such"

I totally understand, and your questions are good. But lets face it, dyno numbers dont mean that much, flow bench numbers dont mean that much, nor do the hp figures, especially if the specifications are askew. There is no consistency.

I am more concerned with performance and reliability, not some number on a sheet. First you have to have the ability to finish to finish first.

I am not knocking your cars, I am just doing this work, recording this data, and sharing it with you all. THis is what we have found and am willing to share it with you so that you have a better ability to make informed decisions.

 

Just my two little cents in this area - Using an engine or any piece of machinery that has been carefully and thoughtfully put together is a wonderful thing!

 

Anyone who puts in the time and effort deserves a , so calling bull **** on a machinist is kind of like "Joe" telling the brain surgeon he doesn't know what he sees. I'm just wondering if it was warped during disassembly... not knocking Darkhorse of course. I just can't see the engines running so long and strong that far out of "wack".

 

You would be amazed at what can run. This is an extreme case, but an example that is relevant to this discussion. I just did a cylinder head for a racing Jeep that was sent up to me that had just had a "full rebuild" done to it, it was driven for about 800 miles, but the owner stated that it didnt feel that much different than before. Mind you that he had a bunch of modifications done to it while it was apart that were supposed to give more performance, yet when it was running, it basically ran like crap. So they pulled it back apart and sent it up here for me to look at. Take a look at the pics below of the valve seats, These pics showthe beginning of the valve seat grinding, when you initially come down and just touch the seat to see where the contact between the stone and the seat is.

Let me explain, on a job where the valve guides get replaced, you must redo the valve seat because the valve guide will never go back in perfectly straight and that means that the valve when it sits in the guide is now no longer concentric with the seat, so you go in and pilot off the new guide and grind the seats based off of that- this makes the valve sit centrally in the seat and it will seat and perform properly.

On this head in question, I did not touch the guides, they had already been done, all I did was lick them with a hone to make sure that they were to size (They deviated by almost .002) and free from any high spots. The valve seats had already been done, well supposedly. You take a look at the pics and you will get the idea FYI- the shiny area is where the 45 degree seat stone hits, that is the area of the valve face that seals against the seat.

But this motor "Ran"

 

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look at where the contact stops on this seat, this means that when the valve is closed, there was still a gap between the seat and the valve, and you lose whatever preesure is in the combustion chamber

 

Hi,

Thanks for posting the pics and information. And I feel superz had a reasonable point. But regardless of that, the presentation of photo's and technical information here is excellent. It is always good to learn from a "fussy" craftsman.

Speedlimit...

 

Attention to details. Great work.

 

I am not gay but I LOVE THIS GUY THAT I CAN KISS HIM EVERYTIME I SEE HIM .