Chevrolet over head conversion valve issues

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Chevrolet over head conversion valve issues

Post by Mark Gregush » Thu Jun 11, 2020 12:57 pm

I took the Chevrolet overhead off last year because the exhaust valves were hanging up and was getting backfire through the carburetor. I don't think it was a spring issue as they are a little stronger then stock. I think I am running into maybe two issues; used wrong type of valve and might needed about .001 smaller stems. The seats are 3 angle with the contact area being about 1/16" wide. Looking at the Manley catalog and cross reference to the size I need, the closest match would have the 44 degree head for the exhaust type valves. When I installed the valves I used all intake type and as the photo should show, the exhausts are a bit burnt. The hang up may be caused by carbon in the guide or expansion of the head and or valve stem. This is something that came on over time, not right away. I am thinking a long the lines of getting the 44 degree valves and lapping them in, I don't have inserts. The seat are cut for 45 degrees. A little more back story; When I put this together I used 2 piece push rods with allen head cap screws on the rocker arms for sockets. Because of the size of the recess it is very possible that the push rod was shifting position and not allowing the valve to close all the way. When the head goes back on, I am going to go back to ball and socket, ball being on the rocker arm, but will keep the 2 piece push rods. Oh for ignition I was running the coils off the magneto and an OS-1 carburetor. The photo of the valves shows the intake, exhaust and new intake type valve.
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Re: Chevrolet over head conversion valve issues

Post by Mark Gregush » Thu Jun 11, 2020 1:18 pm

In case you are wondering how I mounted the coil box;
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Re: Chevrolet over head conversion valve issues

Post by Henry K. Lee » Thu Jun 11, 2020 1:43 pm

Mark,

What cam are you using?

Some of the issues you are en-countering are due to week valve springs, possibly not enough trueing of the valve spring bosses in the recesses, and a slight shortening of the cast valve guides. Will post you some photos later as what R&D we have been through.

Hank

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Re: Chevrolet over head conversion valve issues

Post by Mark Gregush » Thu Jun 11, 2020 2:08 pm

Henry K. Lee wrote:
Thu Jun 11, 2020 1:43 pm
Mark,

What cam are you using?
It is what Rick Carnage called a touring grind, somewhere between 260 and 280.

Some of the issues you are en-countering are due to week valve springs,
I will have to compare the springs I am using to what stock called for, the ones I used should have been a little higher then stock.

possibly not enough trueing of the valve spring bosses in the recesses,
?

and a slight shortening of the cast valve guides.
Yes the guides were cut down a little and pocket for oiling

Will post you some photos later as what R&D we have been through.

Hank
When I first started this project I was using the stock springs that were not as strong as they should have been with no issues that I could see or feel had the car up to over 50 on the flat and was using a VW 28 carb too boot. The springs I replaced them with when checked in open and closed were a little higher.
Here is the information I was working from;
http://chevy.oldcarmanualproject.com/ch ... o/2804.htm
Maybe I need to go back and recheck by installing a valve in one of the other heads I have, using the Chevrolet original setup to see if the measurements I was using work out. Quick check, the spring height both original and modern retainer is approx 1.721 with valve closed.
Last edited by Mark Gregush on Thu Jun 11, 2020 2:35 pm, edited 1 time in total.
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Re: Chevrolet over head conversion valve issues

Post by Rich Eagle » Thu Jun 11, 2020 2:33 pm

I had the same thing happen to one exhaust valve on my roof head. The bronze sleeve inside the new guides were grabbing and eventually sliding down.
Just another possibility.
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When did I do that?

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Re: Chevrolet over head conversion valve issues

Post by Mark Gregush » Thu Jun 11, 2020 2:36 pm

No sleeves in this one, just original cast iron.
If I am doing things right (LOL)
Stock Chevrolet: .300 valve travel and open valve is 65 LB at 1.421 (1.721"- .300, both original and modern keepers are approx the same closed space)
Using the number give in the link for closed valve of 39-43 LBS for closed valve at 1.721. 260/280 cam I should be able to check the springs against stock requirement. I will have to wait till Friday to check. Without pulling the head I don't think my dial indicator will reach down to the valve to check the actual lift through the spark plug hole and I know I don't have tools to check lift via the valve chamber.
Last edited by Mark Gregush on Fri Jun 12, 2020 9:27 am, edited 2 times in total.
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Re: Chevrolet over head conversion valve issues

Post by Kevin Pharis » Thu Jun 11, 2020 2:54 pm

Usual fixes for a chebby include;

1) Painting the motor a brighter orange color
2) Chrome plating the engine accessories
3) Making a larger car show build sign
4) Installing a larger carburetor... or multiple
5) More cam... ALWAYS more cam!

Of course... this is not a complete list of potential fixes, results may vary. I just couldn’t help myself :lol:

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Re: Chevrolet over head conversion valve issues

Post by Mark Gregush » Thu Jun 11, 2020 3:10 pm

Ha Ha! My Friend Don's T engine is already Chevrolet orange. :lol: So I guess the 21" Chevrolet disk wheels would be really bad and transplanting the Chevrolet block on and keeping the T transmission and magneto? ;)
I know the voices aren't real but damn they have some good ideas! :shock:

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Re: Chevrolet over head conversion valve issues

Post by Kevin Pharis » Thu Jun 11, 2020 3:24 pm

All should be good as long as you keep the delicate “orange to chrome” ratio in balance... you may have to start chroming chassis components eventually 🤔

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Re: Chevrolet over head conversion valve issues

Post by Mark Gregush » Thu Jun 11, 2020 3:35 pm

What color should I paint the 490 steering box?
Ah heck it's got a Warford and big drum rear end with Rocky Mtn brakes now. To balance things out, the 25 is keeping cast iron pistons even when I redo the engine. if you haven't seen it in Off Topic's, I may be adding a 1920 Dodge touring to the stable soon. :twisted: It even has a Model T part on it, the steering wheel rim.
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Re: Chevrolet over head conversion valve issues

Post by Henry K. Lee » Thu Jun 11, 2020 3:54 pm

Talk about throwing Mama under the bus! Ouch Kevin! Chevy High Gloss Black cures all!

Give me a side photo of your #1 cylinder valves on top dead center. If your rocker arms are not set at the correct angle of contact, you are in a bind. Remember, that is a “B” series head, rocker ratio is 1.33 to 1 X cam lift. Sounds stupid but after they heat up, clearances close up and the tip of the rocker slips into a mild bind.

Just Saying been there done that. Sometimes rechecking the rocker contact alignment and slightly redressing the tips is all it takes. Your other specs sound Great Mark.

Hope this Helps,

Hank

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Re: Chevrolet over head conversion valve issues

Post by Mark Gregush » Thu Jun 11, 2020 4:09 pm

Kevin's comments are giving me a chuckle, no more no less. :lol:
RE Without pulling the head
The Chevrolet head is off and T head back on. The valves I have installed are within a few thousands of the stock Chevrolet in length so rocker arm angle should be the same. I could install the valves loose with rocker arm an get a photo if needed. ? But you said "B" and 1.33:1, wouldn't that be RAJO?
Update; The valve do travel down more with the lift from the T cam because the lobes on the T cam are higher.
Last edited by Mark Gregush on Fri Jun 12, 2020 9:30 am, edited 1 time in total.
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Re: Chevrolet over head conversion valve issues

Post by Kevin Pharis » Thu Jun 11, 2020 4:55 pm

Mark Gregush wrote:
Thu Jun 11, 2020 4:09 pm
Kevin's comments are giving me a chuckle, no more no less. :lol:
👍😉



As for your assembled valve height and rocker arm angles... It’s not difficult to check your geometry, and will change very quickly dependent on a couple factors.

Assembled valve height will need to vary depending upon the lift of your cam. The idea is that the valve is at the same height as the rocker shaft at mid lift. You can pretty easily measure the rocker shaft centerline height with a pair of dial calipers and some patience. Then simply add half of your cam lift (at the valve) to the centerline height. Here is a pic of my Akron-Hed during this very process. The spacers were used to help me find the actual rocker ratio, and assembled valve height based on the cam lift I hope to run.

CE1830FD-4DDA-49A2-A749-8EA51431C9D8.jpeg

Keep in mind also that the same geometry rules apply to the pushrod side of the rocker arm. It is best to adjust the push rod length up to the rocker arm adjusting screw at an ideal position

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Re: Chevrolet over head conversion valve issues

Post by Henry K. Lee » Thu Jun 11, 2020 4:56 pm

Chevy made an “A” series head, one to one ratio. Then they came up with the “B” series head twin port in and out with the 1.33 to 1 ratios.


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Re: Chevrolet over head conversion valve issues

Post by Kevin Pharis » Thu Jun 11, 2020 4:59 pm

Mark Gregush wrote:
Thu Jun 11, 2020 4:09 pm
you said "B" and 1.33:1, wouldn't that be RAJO?
I’m pretty sure the “B” referrers to the dual intake port design (‘26-‘28), rather than the single intake port earlier design (I’m no chebby expert). And the rocker ratio is whatever it is... only way to confirm, is to measure

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Re: Chevrolet over head conversion valve issues

Post by Mark Gregush » Thu Jun 11, 2020 5:17 pm

Got the B thing now. I thought the rockers were 1.5:1 on this head? Here are a couple of shots with the valves closed, No 4 are stock Chevrolet valves and No 3 are the replacements, I took shots with valves open but forgot to take into account the multiplying factor so will need to redo.
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Last edited by Mark Gregush on Fri Jun 12, 2020 9:31 am, edited 1 time in total.
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Re: Chevrolet over head conversion valve issues

Post by Mark Gregush » Thu Jun 11, 2020 5:35 pm

My calculations of the spring height at open is off, I was doing it at 1:1 not 1.33:1. I am going to take a break from it today, I need to get some other things done. Not dropping it and will get back to it shortly, maybe this weekend or later today. Oh by the way, I set my gaps with the engine up to temp, maybe not as warm as on long drive, so gaps should be ok.
Thanks guys.
Did a little more checking, the Chevrolet cam has about .190 lift (worn) X 1.33 put it in the ball park of the valves opening .300. So I was off. With a .260 T cam, that would be about .3458 approx that the valves open, so is greater then not less then the Chevrolet cam. Subtracting the gap allowance of about .010 would be about .335-.3358. My head hurts! ;)
While the base height of the spring remains the same at 1.721 and with a spacer on the spring I can get about 45LBS with the valve closed so now have to recheck what it will be with the valve open.
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Re: Chevrolet over head conversion valve issues

Post by Cordes_jeff » Fri Jun 12, 2020 4:55 pm

I run hardened seats and valves from a 90s olds I believe. Springs are VS468. Have never had a problem with the valve train. Blown head gaskets are another story.

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Re: Chevrolet over head conversion valve issues

Post by Henry K. Lee » Fri Jun 12, 2020 5:15 pm

Mark,

You do good work on taking pictures!

It appears you do not have enough radius grind/polish on the tips. Using a rocker arm attachment on an older model Sioux Valve Grinder to ratio angle would really help. Lack of angle/introduction causes a binding to occur thus preventing the valve to rotate naturally and will cause them to stick. I believe this is where your bad pixie is hiding.

Hope this Helps and all the Best,

Hank

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Re: Chevrolet over head conversion valve issues

Post by Henry K. Lee » Fri Jun 12, 2020 5:21 pm

As a side note:

You are probably hearing more valve clatter than normal when this occurs, but at cold state your clearances are still around 0.012".

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Re: Chevrolet over head conversion valve issues

Post by Henry K. Lee » Fri Jun 12, 2020 6:20 pm

Second side note:

After re-grinding/polishing is done I normally re-harden the ends and take a hand wet stone for the final finish. Really Helps!

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Re: Chevrolet over head conversion valve issues

Post by Mark Gregush » Fri Jun 12, 2020 7:41 pm

RE the radius, I sorta was thinking about that yesterday looking at the pads. Not something I really know about but sorta can picture what and why.
https://www.ebay.com/itm/SIOUX-VALVE-GR ... Swxbhe1Dz1

I was thinking maybe some of the pads looked a little flat and that they might not slide/roll across the end, not thinking that it would causes problems. I will have to take a look in the Black and Decker we have at the shop, I did a long time ago when we first got it, might be an attachment that at the time didn't know what it was for. There are a lot of dodads and what-nots in the cabinet.

While we are on the subject of the valve train, I noted that the exhaust lobes on the Chevrolet cam are more flat across the end so the valve stays open a little longer. The intakes are pointed so they ramp open and closed quickly. Looking at a Model A cam that we think is full race, both the intake and exhaust lobes are a little flat too, but not as much as the Chevrolet exhaust. Would there be any benefit to keeping the same cam lift but getting the exhaust lobes ground to the Chevrolet profile?
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Re: Chevrolet over head conversion valve issues

Post by Mark Gregush » Fri Jun 12, 2020 8:48 pm

Ok so I looked at the pads on the ones I was using, not as bad as I thought but need attention. The one, top row, 2ed from the right has cuts running through it. The rest if not radius-ed need to be smoothed. Looked at the other set in my parts, yck! They need even more work. The two cam photos are the 28ish Chevrolet cam. RE the radius on the pad, good info for anyone installing an overhead, RAJO etc.
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DSCN0362.JPG
DSCN0364.JPG
DSCN0365.JPG
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Re: Chevrolet over head conversion valve issues

Post by Henry K. Lee » Fri Jun 12, 2020 9:02 pm

Mark,

Just trying to help with experience and knowledge gained. Those rockers in my opinion do need to be polished up. Minor rust pits, looks like one has been on a belt sander (cross sanding), etc will cause drag with relative pressure. From your first pictures the high soot and lack of contact on the middle valve is a give away of this occurring. When you redress them and polish, you will notice a big difference!

Hope this helped you and Others!

All the Best,

Hank

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Re: Chevrolet over head conversion valve issues

Post by Henry K. Lee » Fri Jun 12, 2020 9:13 pm

Here are some photos of a stock valve guide boss.
IMG_1667.jpeg

Here is after a trueing of the sides and decking to the main casting height.
IMG_1663.jpeg

I make my own tool, using multiple bimetal hole saws glued together with JB Weld (it is only cast iron and cuts like butter)
IMG_1666.jpeg

Simple valve springs used.
IMG_1664.jpeg

Hope this Helps Ya'll!

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Re: Chevrolet over head conversion valve issues

Post by Mark Gregush » Fri Jun 12, 2020 9:50 pm

When I did my bosses, I counter bored them, then drilled an oil well as original. The only reason I did the counter boar was because the modern spring retainers came down too far. I'll post some photos tomorrow. I agree on the pads needing attention. They are pretty snarky. Thank you for the information, I am sure I am not alone in needing this heads up. Should add, the valves shown are from the front two cylinder, the back ones don't look like that, they all still have shine on the contact surface.
Last edited by Mark Gregush on Sun Jun 14, 2020 11:59 am, edited 1 time in total.
I know the voices aren't real but damn they have some good ideas! :shock:

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Re: Chevrolet over head conversion valve issues

Post by Mark Gregush » Sat Jun 13, 2020 5:54 pm

Few more photos. The Black & Decker holder for doing rocker arm pads and how I did the bosses. I am still working on freeing the adjustable cone on the rocker arm holder. I don't think it's threaded, if it was, there would be a flat knurled area to turn it. Tried a little heat and paraffin but she no move. The knurled piece at the bottom is not attached to the cones, it clamps the center shaft to the bracket, the top one is not attached ether, it locks the adjustable cone in place after the rocker is installed.
Update; I got the cone loose. It was a little rusted in place. I have been reading some postings on the subject on pads. Some of the post seem to indicate that as the pad wipes the end of the valve stem it turns the valve too. Trying to figure that one out?
Attachments
DSCN0373.JPG
DSCN0371.JPG
DSCN0370.JPG
DSCN0368.JPG
DSCN0367.JPG
I know the voices aren't real but damn they have some good ideas! :shock:

1925 Cut down pickup
1920 Dodge touring
1948 Ford F2 pickup

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