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PostPosted: Tue May 22, 2018 4:37 am 
356 Fan

Joined: Sat Apr 09, 2011 11:08 pm
Posts: 4
Hello fellow 356ers,

I am currently rebuilding the top end of my 1963 T6 B Super engine at a friends workshop and have run into the following problem.

The last rebuild of the matching numbers engine was well over 120,000 miles ago. It was a runner before our disassembly. We're only redoing the top end - bottom end has been left intact.
Crank end play is within spec, cam still looks good, followers look fine, connecting rods look fine, small end bushes are tight and the new big bore kit fitted beautifully.
Heads have been flycut previously
Heads have now been completely refinished by an outside machine shop due to having 3 cracked combustion chambers
All new valve guides, intake and exhaust valve seats and intake valves. Exhaust valves were ok, as they were replaced a few years ago. All existing valve springs were within spec and reused.
Fitted new big bore forged pistons and AA 86mm biral cylinders - replacing the previous cast iron 86mm big bore kit.
Deck height appears to be matched to the previous deck height and we have shimmed the cylinders accordingly - although we have not verified deck height at this point, but we will do so. Let's assume the deck height is ok for the sake of this discussion - the crank turns over freely.
My guess is that as a result of adding new material to the heads to repair the cracks and cutting the new valve seats, the valves now sit higher in the combustion chambers than they used to - and with wear, they will continue to move upwards.

With the newly rebuilt heads, there is now insufficient adjustment available on all of the rocker arms (with the old B super pushrods fitted) to attain correct valve clearances, ie the rocker adjustment has been backed off to the max and correct valve clearances are unachievable on both the intake and exhaust sides of both heads.

The existing (the old) pushrods measure between 256mm and 257mm.

I am looking at fitting new (shorter) pushrods to this engine so I can achieve the correct valve clearances. I would rather do this than shim the aluminium rocker stands.

The questions are as follows:
1. Just how much adjustment is reasonably available in the rocker arm assemblies on both the intake and exhaust side? I'm aware that with extreme rocker geometry here there is a potential oil starvation issue, so I want to reset the valve adjustment geometry to sit somewhere in its midrange.
2. Is there any unusual issue that you need to take into account when you reduce the length of all pushrods in a 356 engine?
3. I've searched the web and can find 2 shorter pushrod lengths for 356 engines. One is 255.7mm, the other 252.5mm. 255.7 seems not enough of a variation, whilst 252.5 seems too much of a variation.

As we are still in the test fitting phase of rebuilding the engine, any words of wisdom on this subject would be greatly appreciated.

I don't want to mess this up.

Many thanks

Richard

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PostPosted: Tue May 22, 2018 6:46 am 
356 Fan
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Joined: Sat Jun 04, 2016 2:38 pm
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Location: Near Stroud, Gloucestershire, UK
Are you sure the push rods are seated properly in the cam followers.


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PostPosted: Tue May 22, 2018 8:17 am 
356 Fan
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Joined: Fri Oct 23, 2009 7:24 pm
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Location: 30MI WEST OF PHILA
The solution is to place link pin shims under the rocker stands. This is a common problem.

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PostPosted: Tue May 22, 2018 10:19 am 
356 Fan

Joined: Sun Apr 20, 2008 12:54 am
Posts: 2870
Richard,

Since the heads were fly-cut and hopefully the cylinder seat depths of 9,5mm match each other w/in .0004-.0005",
you must check the exhaust valve clearance-to-piston @ top dead center using a soft lead piece of a stiff clay;
Common clearance to be around .040"-.045". Also, the cylinder heights should match each other w/in .001.

With the rocker assembly along w/the pushrods installed, the adjustment screws setting the valve clearances,
make sure the screws will turn outward w/2-turns so the rocker allows oil to pass thru from the pushrods to the
rocker shafts! If not, add an equal amount of link-pin shims under the rocker stand(s)

Dick


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PostPosted: Tue May 22, 2018 12:26 pm 
356 Fan
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Joined: Wed Aug 27, 2008 10:54 am
Posts: 2051
Location: Alpine AZ, Green Valley AZ
I think your question has been answered OK, but can I ask why, when you are this far into the engine, you don't also split the case and check the crank and main and rod bearings? The top end rebuild that you are doing is going to put a little more stress on the bottom end.

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PostPosted: Tue May 22, 2018 6:39 pm 
356 Fan

Joined: Sat Apr 09, 2011 11:08 pm
Posts: 4
Thanks for the responses everyone,

So no one has ever gone down the route of installing shorter pushrods? How come? These are fundamentally the questions I have.

Given that I'm going to source new pushrods anyway, I thought this would be a better way to go than introducing shims under the rocker stands.

We're leaving the bottom end intact because in my nearly 25 years of ownership of this car, oil changes have never exceeded 3000 miles, there has never been an issue regarding the bottom end of the engine, there has never been an over rev, though I always keep the rpm's in the "happy zone" above 3000 rpm, and my local brains trust of original owners and long term knowledgeable enthusiasts favour me to stick with the "if it aint broke, don't fix it" mantra. If the crank end play was out, the connecting rod bearings were overly loose or the small ends of the connecting rods were a sloppy fit, I'd be more inclined to delve deeper, but they're not.

This refresher has the benefit of removing around 600 to 700 grams of weight from these top end moving parts - which has to be a positive for bottom end longevity. I'm aware the refreshed top end performance may place more demands on the older bottom end and it's a risk I'm prepared to accept.

Only hindsight will reveal what the "correct" rebuild decision really is..... but such is life.

Many thanks

Richard

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PostPosted: Tue May 22, 2018 7:28 pm 
356 Fan
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Joined: Fri Oct 23, 2009 7:24 pm
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Location: 30MI WEST OF PHILA
Usually a rebuild does not require new pushrods so shims are the smart solution. Before you buy shorter pushrods take a look at your rocker arm geometry. When valves have been feddled and rocker stands repositioned and heads repositioned you may find that the rockers aren't contacting the valves correctly. The rockers should be reground also.

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PostPosted: Tue May 22, 2018 8:25 pm 
356 Fan

Joined: Tue May 31, 2011 10:07 pm
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Location: VT
Probably worth replacing all valve springs. Inexpensive peace of mind and much easier to do it now.


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PostPosted: Tue May 22, 2018 9:16 pm 
356 Fan
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I'm also in the 'do the bottom, too,' camp, but it's your engine.
If by any chance you saved any of the last oil drain, you could prove your point (or reconsider) by sending it to a place like this: https://www.tricocorp.com/services/oil-analysis/
The DFV got a pint sent to a local outfit after every race, and given the cost for those parts, the $35 charge was a rounding error. What they reported then (25 years back?) was amazing, and I'll bet it's better now. They didn't tell you which rod bearing was losing too much metal, but they sure told you you'd better find out.
BTW, no matter whose 'kit' you buy, I'd also stick some decent filtration on it to keep those bearings healthy.

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PostPosted: Tue May 22, 2018 10:08 pm 
356 Fan

Joined: Wed Nov 23, 2011 10:52 am
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Location: Cleveland, Ohio
I would at least inspect the bottom end. Just because a crappy Neon still runs OK at 180K miles doesn't mean your 1963 engine would last like that. They seldom did.

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PostPosted: Wed May 23, 2018 12:45 pm 
356 Fan
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Location: Alpine AZ, Green Valley AZ
My main reason for asking is that it isn't really a lot more work to check the bottom end when you are this close. I'd do it just for the peace of mind that it would bring on future spirited drives. What kind of oil pressure did it have before the current work?

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Last edited by Wes Bender on Wed May 23, 2018 4:20 pm, edited 1 time in total.

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PostPosted: Wed May 23, 2018 2:52 pm 
356 Fan

Joined: Tue Mar 25, 2008 6:14 pm
Posts: 199
If you already have the heads and pistons/cylinders off you should at least check rod bearings.

Easy to do without splitting case, if you are careful. You may find some copper showing and I would at least replace rod bearings and nuts on rods and consider splitting case.

Michael Foster

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