Just Got My Head Back - Should I Be P****d??
I've just got my cylinder head back from being worked on and I'm a little uncertain on a few things
I've taken some (bad) pictures and I need your input
The first six pictures are of the chambers, and show how close the inlet and exhaust valves are to each other
Notice how on some of the chambers the seats actually overlap each other.....Is this ok or should I be worried?
(the head is cast iron and it has had inserts fitted to the exhaust to allow the engine to be run on unleaded fuel)
The next five pictures hopefully show the varying depths the seats have been cut into the head
Should they all be flush with the chamber, or does it not matter that some are recessed?
The next picture shows the original inlet valve next to the new (mismatched) valve
The original valves are 65g in weight even when covered in carbon
The new valves are 70g and have a different shape to them
Note - he has only replaced two of the inlet valves with these heavier valves
The new valves have been fitted into the chambers which have had their seats cut deeper than the others
I'm thinking he's obviously fitted these valves because he's cut the seats too deep?
The last two pictures are both of the same chamber
I have taken one picture with one of the original valves in it, and then another picture with the new (heavier & different shaped) valve in it
I don't know if you cam make it out from the picture, but the original valve sits further into the seats than the new valve does
How right am I to be worried about any of this?
I'm pretty pissed that the head came back covered in old paint and carbon, but I can sort that out myself
What I really need help with is knowing whether the machining is good or not, and why are there different valves in the chambers with the recessed seats?
(I can't contact the guy until tomorrow, so I need your input before then so I know what to say to him - if it's even a problem)
Just Got My Head Back - Should I Be P****d??
Install both intake and exhaust valve with springs, retainers and locks. Fill the chamber with some alcohol. It should not leak down if it does you have a problem.
Are the valve tips all the same hieght? If so it was done correctly not all heads can be rebuilt. Also what size valves did you have installed. If the valevs are lowerin the head and longer they would be taller at the tip than all. The others. Looks like the heads were beyond a fisrt time rebuild and needed more work than normal. Not un common. If it all lines up and works then you got the work you asked for.
These may perform a little less than new heads but sometimes it what you get to work with. They will run and be fine on normal street car.
cdminter - Will do, thanks
To confirm.......I do this with the head upside down on the workbench?
hcompton - the valves are all the same length and diameter
It's just the shape of them that's different
The guy told me the valves I had are terrible and that he would throw them all away and replace them with new/better flowing ones
But now I find I've got my original valves with only two replacement ones which don't match
My original valves are readily available
Should I do a leak test assuggested, and if all is well, replace the mismatched valves with the same ones I had to begin with?
The seat overlap is normal.
By mocking up the valves using a light checking spring or even just holding them closed w/your hand you can measure the spring height between the spring seat of the head and the underside of the retainer w/a snap gauge and caliper to see how much the heights actually vary. This gives a direct indication of what the seat placement really is; the chamber volume is not how you judge the seat placement.
If your valves are made to have a stock spec 1.7" spring installed height (they're not +0.100" valves, in other words), compare the measured installed height to 1.7" to see if the seats are sunken or not.
If the installed height is too much for the springs you're going to use, add shims under the springs. Keep the valve seat, valves and shims together once you measure the installed height. Try different valves on different seats to get the best match.
For a street engine, you'd like the intake seats to be >/= 0.060" wide and the exhausts to be >/= 0.080" wide. I wouldn't want to go much more than that, and no less. This is a compromise for durability vs. flow.
You need to blend the lip below the seat's last cut into the bowl. You can lap the valves in if you find they're not sealing as well as they should.
Were the valve guides done on these heads?
post the bill? did the machinist do the "cheapest" job possible or best? was he informed the application? what is the application?( not engine size but actual intent for the engine,IE hot rod or grocery getter? How do you know what valves go in which hole? were the guides replaced?
cobalt - thank you for your reply - extremely reassuring
Not knowing what the original casting looked like. I can see that it has had some guide work. That means the original seat was worn. So some of the depth variance can be due to having to cut the seat a bit more to get a clean seat after the guide work was done.
The exhaust seat depth does vary a bit, but all chambers are not cast in exactly the same height/cc.
The actual seat area looks good for a maintainance valve job. Seat runout and width looks very good. Cut with a profile cutter I would assume.
If this head has an adjustable valve train. Some varience of stem height is allowed. The nominal height/stem protrusion is usually published in the engine rebuild specs.
The aftermkt valves were probably used to get the stem height/chamber volume closer to spec.. A common practice on re-builds.
All told it looks like an acceptable stock replacement valve job with hard seats.
While I'm here. I will tell you of an example I had this past summer.
Two years ago. A customer brings a set of BBC heads in. val port c-chamber early heads. Wants them "rebuilt" going on his hotrod 454. Wants all the best stuff.
By the time they are disassembled (2 weeks) and checked. Like so many people in Michigan. He lost his job.
Now it turns into a "budget job" so he can sell the engine.
The heads needed guides and had at least three/four valve jobs previously. Intake seats were sunk at least .090".
Customer wants them repaired a cheaply as possible. So I knurled the existing guides, something I rarely do. Two of the intake seats were just junk. So I installed new ones. But I had to set them close to the sunken height of the others to maintain some chamber vol. and stem height.
Long story short. The customer comes in last august. "You ruined my heads!" Being two years ago I didn't remember the heads. Of course he didn't have the heads or the original billing. Wants the heads replaced. My bookeeper went back and found all the paper work. No way guy! You got what you paid for.
Seems he had just got the engine running after two years and had a cooling problem. One of his buddies removed the heads (not the cooling problem). Saw the sunken intakes and the stuff hit the fan. Of course its the machinest fault.. I screwed him etc. yada yada yada.. Let no good deed go unpunished.
vinnie - I don't have a bill, this was done by a retired individual that came highly recommended for these engines
The car will be used as a weekend toy, he was told to do the best job he can
(parts are so cheap on these engines it really doesn't matter about the cost)
He received the head in July, and I got it back yesterday
He's written 1-12 on the valves in marker so I know their location
I asked for new guides to be fitted, but he left the old ones in place
I'd heard brass ones are better but he said the ones fitted are fine
If I put my finger over the guide and push/pull the valve it sucks my finger
From yours, and everyone else's comments though, it sounds like I'm good to go
My concern now is the shape and weight variance of the valves
My "original" valves as well as the two replacement ones are both aftermarket
Should I replace them so they all match?
Nothing wrong with iron guides in a street car. Looks like he used bronze liners. When properly installed are better than solid "Brass" (bronze") guides. Which need specialized tools for bronze work. A pain in the rear.
BOBCRMAN posted a very good account of what I was leading into. We all have a different idea as to what perfect is.Not just what you think is perfect,also the machinist. Was he trying to make the best results for the least costs? were you hoping for the best headswith no worry of costs?
Bronze guides are good but do not last long. Knurled guides used to be quite common when I was young and poor. Sinking the valves was a quick way to make a chamber bigger,an so on,,,,
What engine is this? How's it going to be used?
FWIW, my bronze guides have outlasted the cast iron SBC guides in production heads- held the seats better, too.
I'm trying to improve my skills though
I had a go at welding, but everyone told me I was a danger to myself
I've continued practicing, but sent the car to a bodyshop once I found one I was happy with
The bodywork's cost me about twice the value of a fully built show-winner, but I'm not selling mine, and I want everything just right so it doesn't really matter about cost
The car is a Triumph GT6, so it's about as cheap as can be anyway!
|All times are GMT -6. The time now is 03:34 PM.|
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2015, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.