The number of machinists who have seen original 356 heads is growing smaller and there are no specs to go by. The problem is heads that have been rebuilt many times, so the valves are sunk down into the seats, not sitting up like they did when the heads were new. There can be at least 2mm difference, maybe more.Martin Benade wrote: ↑Mon May 16, 2022 11:31 pm It’s true that the seats get deeper but any machine shop guy that knows anything at least estimates how much to shorten the valve stem. It’s standard practice.
When the rocker stands need shimming link pin shims fit perfectly.
Eating Points
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Re: Eating Points Updated
- Harlan Halsey
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Re: Eating Points Updated
James,
Stock street 356 engines usually go 80-100,000 miles between rebuilds. That should mean one or two rebuilds by now. But there seems to be some old junk out there. Parts compromised by incompetent work. Which category does your car fall into? Resurrecting old junk is rarely worth it. Unless you are a hobby machinist (like me) it is better to replace the compromised parts with new ones or good used ones. A 356 head will survive two or three normal rebuilds, and then you can usually replace the valve seats and guides and be like new except for a couple of .010" clean ups of the cylinder seats. Valves can be reground at least once. It should never be necessary to shorten the valve stem on a 356.
Properly set up 356 engines run with the valve adjusters several turns from all the way in. And they stay about the same valve to valve. The easy way to check for clearance is to rotate the pushrod with your gingers. If you don't have clearance, then you will have to disassemble to find out why.
Rocker geometry is important. If the valve has been effectively lengthened by grinding the seats and grinding the valve stem and shortened by cleaning up the stem head, and the head has been lowered by cleaning up the cylinder seats, and the rocker faces have been smoothed to the correct curve, the rocker stand will have to be shimmed to compensate. As Martin notes, link pin shims work well for this and also for leveling the head nuts if the nut seats aren't all the same depth.
Stock street 356 engines usually go 80-100,000 miles between rebuilds. That should mean one or two rebuilds by now. But there seems to be some old junk out there. Parts compromised by incompetent work. Which category does your car fall into? Resurrecting old junk is rarely worth it. Unless you are a hobby machinist (like me) it is better to replace the compromised parts with new ones or good used ones. A 356 head will survive two or three normal rebuilds, and then you can usually replace the valve seats and guides and be like new except for a couple of .010" clean ups of the cylinder seats. Valves can be reground at least once. It should never be necessary to shorten the valve stem on a 356.
Properly set up 356 engines run with the valve adjusters several turns from all the way in. And they stay about the same valve to valve. The easy way to check for clearance is to rotate the pushrod with your gingers. If you don't have clearance, then you will have to disassemble to find out why.
Rocker geometry is important. If the valve has been effectively lengthened by grinding the seats and grinding the valve stem and shortened by cleaning up the stem head, and the head has been lowered by cleaning up the cylinder seats, and the rocker faces have been smoothed to the correct curve, the rocker stand will have to be shimmed to compensate. As Martin notes, link pin shims work well for this and also for leveling the head nuts if the nut seats aren't all the same depth.
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Re: Eating Points
James, here's my take on what is happening. You had a distributor with one piece points, maybe a 031 or some kind of a VW distributor. You replaced it with an 018 which is the cast iron stock 356 distributor. Most of the one piece points distributors are set up to be 90 degrees different than the 018. 90 degrees on the distributor equals 180 degrees at the crank. So when you say the rotor is pointed at the mark for #1, the engine is at TDC for #3. Adjusting the valves in this position #3 would be loose and the #1 would be on the exhaust stroke, with the cam opening the exhaust valve making it impossible to get any clearance. To set it up move the spark plug wires on the cap 90 degrees, yes two of the wires will be on the wrong side of the cap. This is easy, find #3 wire and place it in the cap where the rotor is now, then follow with the rest in order. Then readjust the valves, using the TDC where is now to do #3 then move on to the rest in progression. You said that the engine cranked over but stopped with a thud, that was because the spark fired when the engine was starting its compression stroke, building up pressure.
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Re: Eating Points Updated
Wouldn't grinding seats or fly-cutting normally affect all the valves in a particular head about equally? Only #1 position was mentioned by OP.DaveErickson wrote: ↑Mon May 16, 2022 9:26 pm There are several things that can contribute to the problem. Every time the heads get rebuilt, the seats are ground and the valve stems get higher in the head. If heads are flycut or cleaned up at the cylinder mating surface, it brings the head closer to the case. After many rebuilds, and using used parts, the pushrods don't fit as well as they used to. Problem can be corrected by shorter pushrods or by putting shims between the long head nuts and the rocker arm castings.
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Re: Eating Points
Steve, I think you may have nailed it. When a customer called me about a broken system, my first question was always "What did you change?"Steve Douglas wrote: ↑Tue May 17, 2022 1:21 pm James, here's my take on what is happening. You had a distributor with one piece points, maybe a 031 or some kind of a VW distributor. You replaced it with an 018 which is the cast iron stock 356 distributor. Most of the one piece points distributors are set up to be 90 degrees different than the 018. 90 degrees on the distributor equals 180 degrees at the crank. So when you say the rotor is pointed at the mark for #1, the engine is at TDC for #3.
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Re: Eating Points
Good point on the distributor orientation. I'd bet there is something to that.
On the valves, try setting the number 3 cylinder exhaust valve to all the way open and check the number 1 cylinder again for clearance. This rules out any positioning mistakes because you know if the exhaust valve is all the way open that you are on the base circle at the opposite cylinder.
On the valves, try setting the number 3 cylinder exhaust valve to all the way open and check the number 1 cylinder again for clearance. This rules out any positioning mistakes because you know if the exhaust valve is all the way open that you are on the base circle at the opposite cylinder.
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Re: Eating Points
It's not too hard to determine what's what if the distributer rotor position is in question. Just rotate the crank to TDC. Remove both valve covers. Try to spin the pushrods. Both pushrods will spin easily on the cylinder which is in firing position. Do not rotate the engine with the distributer out!
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Re: Eating Points
If they are adjusted correctly, yes. They won't spin if they are tight.
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Re: Eating Points
Correct,
DON'T turn engine without a dizzy in place. I believe the drive gear will lift and You will Mangle the Drive Gear!
I never found that the Alloy 031 Bosch Dizzy located in a different position to the Bosch 022 . I think Harry said that the 050 does.
At Pulley TDC rotor arm should point to Cylinder 1 (018, 022 & 031 ) It does have the one piece points which I never had a problem with.
Liked the Look but it isn't as robust as Cast Iron. Does it have the same advance curve as the 018 and 022 ?
For the price of 2 Tow Trucks Home You could probably have fitted a 123 Ignition Dizzy and eliminated the problem.
J.I.M.O / 2 cents
Regards Jay
DON'T turn engine without a dizzy in place. I believe the drive gear will lift and You will Mangle the Drive Gear!
I never found that the Alloy 031 Bosch Dizzy located in a different position to the Bosch 022 . I think Harry said that the 050 does.
At Pulley TDC rotor arm should point to Cylinder 1 (018, 022 & 031 ) It does have the one piece points which I never had a problem with.
Liked the Look but it isn't as robust as Cast Iron. Does it have the same advance curve as the 018 and 022 ?
For the price of 2 Tow Trucks Home You could probably have fitted a 123 Ignition Dizzy and eliminated the problem.
J.I.M.O / 2 cents
Regards Jay
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Re: Eating Points
I think only turning the engine backwards is a problem with no distributor.
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Re: Eating Points
I did have a 050 for a while then about a year ago went with an 033. I knew of the 90 rotation of the 050 and turned it back and it ran for a long time. After shipping the car back I’ve had problems. First it was the right Zenith leaking. I fixed that then the points closed. Not sure why. I’ll check the other valves and check their movement. Yes two tow jobs and I could have bought a lot of anything. Thanks for some good ideas.
James Penland
- Brian R Adams
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Re: Eating Points
The 050 definitely orients 90-deg out from the BR18. I bought a new Brazilian 050 for a great price decades ago strictly as a spare. It has paid for itself as a quick way to isolate the BR18 in debugging tuning problems. Also ran the car with it satisfactorily, albeit with a its linear advance curve, while the BR18 was away for rebuild two different times.
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Re: Eating Points
Gammatronix +1