Valve gap grows on my 74f rebuild (1 Viewer)

rsbcruiser

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Knurling valve guides is a used car lot fix, a term known among them as "good e-nuff to get it off the lot" repair....IIRC you said the motor had 3 or 4K on it since the repair? if so thats about a normal length of time before you start noticing some issues.....

Thanks Grant, actually I started noticing problems right out of the box. At first I blamed it on break in but I soon started thinking that 0.020"+ adjustment and the occasional tight as can be valve gap probably weren't normal. Ya, the knurling thing, never going there again. New guides are just not that expensive (saying this before I get the bill, of course). man oh man, my first full on engine job. Fragged! Doing it right this time.
 

rsbcruiser

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Heads back from the rebuilder

Picked up my rebuilt head along with a box of near new Downey springs. They removed the Downey springs, maintaining that they were wrong, replacing them with an 85lb spring. Still more than the stock Toy valve springs I think. They'll figure all that out when they get the block and cam. Picture shows the new valves, yep all new with solid stainless exhaust valves, ported intake and exhaust, Three sets of valve springs now, the old stock toys, the Downeys and the new ones, humm.
rebuilthead1.jpg
 

rsbcruiser

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What was the problem with the Downey springs?

Dudes down at Bearing Services said they were the wrong diameter. The ID of the sring coil was too small for the valve seals. The seals rubbed against the coils. When I brought up the subject, the Downey RV cam and all, they himmed and haad saying the Downeys were just Chevy springs, maybe they will work, refund on their replacements maybe. They'll take a look at my cam, make things work. I have a feeling the Downeys' will be back on there before all is said and done.
 
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Dudes down at Bearing Services said they were the wrong diameter. The ID of the sring coil was too small for the valve seals. The seals rubbed against the coils. When I brought up the subject, the Downey RV cam and all, they himmed and haad saying the Downeys were just Chevy springs, maybe they will work, refund on their replacements maybe. They'll take a look at my cam, make things work. I have a feeling the Downeys' will be back on there before all is said and done.

That sounds a bit strange. Either the ID of the springs was too small, or it wasn't. Should be pretty easy to tell. Then again, maybe when the guides grenaded, that caused enough wobble to make the seals rub.
 
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Sounds as if they are using the umbrella type seals, they don't work w/ Downey springs... I've always used the Felpro Posi-lock, no clearance issues there.....
 
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I don't think you want to get carried away with any super duper valve springs on this tractor motor. If you increase the spring rate, you will increase wear on the cam lobes and increase the pounding on the valve seats. The stock springs are good for at least 5,500 RPM and a little valve float above that might be a good thing to cut back the power before a rod and the crankshaft part ways.
 

rsbcruiser

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Grant, not sure what brand valve seals they used but thanks for the tip on the felpro seals. Ya IDave it's a wierd thing, the Downey valve springs have that flat coil spring that rides inside the round coil, you might have seen them before, alot of the chevy high pro srings have that design. My new srings do not have that inner coil. I am sure the answer to this dilemna is only a phone call to Downey away. I tend to agree with Pin_heads comment. If the new springs can tolerate the lift from the Downey torque cam then that is the way I will go if just to reduce the loads on the valve train. I've been told that the stock springs will bind at around .400" lift, With a .440" on the intake there is reason for concern. Another question, can a light sring cause lifter lift-off on a high lift cam?
 

Trollhole

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The Man-A-Fre cam specs are 262 duration. They don't mention anything about getting new spring but new lifters. I've heard two different stories. I don't want to hose up my engine just because I was to cheap to buy new springs and then they end up breaking and dropping a valve.

So will stock springs work just fine on an rv cam?
 

rsbcruiser

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The Man-A-Fre cam specs are 262 duration. They don't mention anything about getting new spring but new lifters. I've heard two different stories. I don't want to hose up my engine just because I was to cheap to buy new springs and then they end up breaking and dropping a valve.

So will stock springs work just fine on an rv cam?

You bought the Man-a-fre rv cam TH? The Downey has a 216 duration. The spring binding issue might have more to do with lift though. The Downey has a lift of.440" on both the intake and exhaust. I chose it because it had much less valve overlap than other cams. I was shooting for some gas mileage and a little performance. Interesting though, The guys down at Bearing Services said that they will commonly grind some of the duration out of a stock cam, decreasing the overlap. More head scratching there. And TH, I am not sure if spring bind can cause spring failure. Now we both get to scratch head on this one.
 

rsbcruiser

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rsbcruiser, whats your intentions with this build?

My aim is to build an engine that will last a while. While pulling is no big deal (well, sorta) I sure would like to pay attention and money to other pressing matters on the ol pig. What I am looking for is an engine that will produce copious quantities of torque at low rpms. definetely not interested in making a revver out of it. The f engine you know, suffers from a 40s' cam design. Enough valve overlap to guarantee the engine will run when worn. So much that alot of the fuel goes down the exhaust. That was the reason I chose the Downey cam, less valve overlap. Now Bearing Services tells me about their cam regrind. I bet the way to good mileage and some performance would be to regrind the stock cam to less duration and bump the compresion up to say 10 to 1.
 

rsbcruiser

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So whats the specs on the cam from Bearing Services??

Actually grant, I didn't get the whole skinny on their grind. I know they grind to a 265 duration in. and ex..So, another cam with probably more valve overlap than I want. Most f engine grinds are like that.
 

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