1966 427/ 390

[Kevin B.]

Gents- I'm gathering up parts to "freshen up" the 427/390 in my 66. I have owned this car since 1973 and was last in the bottom end in about 1980, but I had the heads off in the mid 90's for valve guides. I'm the only person that has worked on it in this time period, so if my memory holds (that's the big risk!!) I have a good idea of what's in it now.

My goal is to get as close to a fine running factory motor (characteristics and longevity) as I can at this date. To do this I'm trying to stick to GM parts where available, Federal Mogul/ Sealed power where I have to. Trouble is, a lot of the Mark lV stuff just ain't available from GM any more. Do any of you BB experts know if the long slot rocker arm kit 12368085 listed in the GMPP catalog is the same as the old BB rockers? Would sealed power R866R be a better choice? Has anyone tried one? What valve springs would be best for my app? GMPP shows 88963934 for the dual spring, but it shows OD as 1.540" and this seems too large for the MK lV heads. Has anyone used the Sealed power VS-708? What about the Sealed Power cam kit CS1093M for a direct replacement. I know I will have to cut a groove in the rear journal, but that's not an issue, as I have an old cam to take measurements off of. What rods would be best? A PO honed the ones in the motor now for .003" OS wrist pins, and I want to go back to spec.

Thanks for letting me benefit from you guys experience!

[Joe L.]

Re: 1966 427/ 390

Gents- I'm gathering up parts to "freshen up" the 427/390 in my 66. I have owned this car since 1973 and was last in the bottom end in about 1980, but I had the heads off in the mid 90's for valve guides. I'm the only person that has worked on it in this time period, so if my memory holds (that's the big risk!!) I have a good idea of what's in it now.

My goal is to get as close to a fine running factory motor (characteristics and longevity) as I can at this date. To do this I'm trying to stick to GM parts where available, Federal Mogul/ Sealed power where I have to. Trouble is, a lot of the Mark lV stuff just ain't available from GM any more. Do any of you BB experts know if the long slot rocker arm kit 12368085 listed in the GMPP catalog is the same as the old BB rockers? Would sealed power R866R be a better choice? Has anyone tried one? What valve springs would be best for my app? GMPP shows 88963934 for the dual spring, but it shows OD as 1.540" and this seems too large for the MK lV heads. Has anyone used the Sealed power VS-708? What about the Sealed Power cam kit CS1093M for a direct replacement. I know I will have to cut a groove in the rear journal, but that's not an issue, as I have an old cam to take measurements off of. What rods would be best? A PO honed the ones in the motor now for .003" OS wrist pins, and I want to go back to spec.

Thanks for letting me benefit from you guys experience!

Kevin-------


GM kit #12368085 contains 16 GM #3959182 rocker arms. The 3959182 was not the rocker arm originally used for your engine. It was used for late 1969 L-88, ZL-1, and 1971 LS-6. This is a "long slot" rocker arm for higher lift camshafts. However, it will work perfectly for your application and the kit is a good buy. Your engine originally used GM #3860305 rocker arms. These are usually unstamped. They were replaced by GM #6258611 which are stamped "M". The latter are now discontinued, though. My recommendation is to use the 3959182 rockers in the 12368085 kit. These should be stamped "H". If you choose to go aftermarket with a stock-type rocker arm, I'd use Crane Nitro-Carb rocker arms.

Your engine originally used valve springs GM #3859911. This was a single spring with damper. If by chance you still have these on your engine, I'd get them off as quickly as possible. They are notorious for breaking. Of course, if you do still have these valve springs, yours would have been in service for 50 years now. I guess that would make them "tried-and-true". But, I still wouldn't want them on my engine.

The VS-708 is absolutely identical to the spring contained in the GM #3970627. The latter is GM-discontinued but was the absolute best valve spring EVER released by GM for a street big block. Absolutely the best. Period. They were used in PRODUCTION for all 1970-72 Corvette big blocks and were SERVICE for all 1965-69. I have examined the VS-708 and the GM #3970627 carefully and I'm convinced they originate from the same manufacturing source. As some of you know, I generally do not consider that aftermarket (including Federal-Mogul which is an OEM supplier) is the same as GM. However, in this case, I believe they are the same. There is one problem, though. In order to use these springs you have to also use valve spring cap ("retainer") GM #3964264. The latter are GM-discontinued and were never available in the aftermarket. These caps have an integral umbrella-type valve seal. The standard valve stem mounted umbrella seals originally used for your engine cannot be used with these valve springs.

The Sealed Power duplicate of the GM #3883986 is going to be your best bet as the GM cams are long-since discontinued.

Are the rods honed for floating piston pins? If so, they could probably be bushed back to standard size. You could use rods GM #19170198 which are LS-6 rods with 7/16" rod bolts. You might have to slightly relieve the lower crankcase for clearance and you'll definitely have to have the reciprocating assembly balanced (as you should anyway). The biggest problem might be the cost. These rods GM list for 132 bucks each.

[Duke W.]

Re: 1966 427/ 390

It sounds like you want to rebuild the entire engine, but since the bottom end was done in 1980 and the heads were refreshed in 1990 I question the need.

How many miles since the above two jobs were done, what it total mileage, and what is your current rate of mileage accumulation?

Are there any significant problems with the engine that would indicate a need for a complete rebuild?

Sometimes the best course is to follow the old adage: If it works don't fix it.

Duke

[Duke W.]

Re: 1966 427/ 390

Kevin-------



There is one problem, though. In order to use these springs you have to also use valve spring cap ("retainer") GM #3964264. The latter are GM-discontinued and were never available in the aftermarket. These caps have an integral umbrella-type valve seal. The standard valve stem mounted umbrella seals originally used for your engine cannot be used with these valve springs.

The Sealed Power duplicate of the GM #3883986 is going to be your best bet as the GM cams are long-since discontinued.

So, Joe, what kind of seal arrangement should be used with the F-M VS-708 spring and duplicate of the ...986 cap?

Duke

[Joe L.]

Re: 1966 427/ 390

So, Joe, what kind of seal arrangement should be used with the F-M VS-708 spring and duplicate of the ...986 cap?

Duke

Duke------

The only seal that MIGHT work with the VS-708 valve spring would be a positive type seal. However, this would require valve guide machining and I'm not sure there would still be adequate clearance between the inner spring and the valve seal. There might be a few on the market that might work, though. Even if that obstacle was surmounted there would still be the problem of a properly configured valve cap to work with the valve spring configuration. No aftermarket equivalent of the GM #3964264 cap was ever or is now available. Even Sealed Power specifies that the VS-708 valve spring must be used with the GM #3964264 cap.

What's the "986" cap?

[Joe L.]

Re: 1966 427/ 390

It sounds like you want to rebuild the entire engine, but since the bottom end was done in 1980 and the heads were refreshed in 1990 I question the need.

How many miles since the above two jobs were done, what it total mileage, and what is your current rate of mileage accumulation?

Are there any significant problems with the engine that would indicate a need for a complete rebuild?

Sometimes the best course is to follow the old adage: If it works don't fix it.

Duke

Duke------


Yes, that's very possible. The engine might not need rebuilding.

[Justin S.]

Re: 1966 427/ 390

I was told that the Felpro SS72513 seal was as close to the original as possible.

[Joe L.]

Re: 1966 427/ 390

I was told that the Felpro SS72513 seal was as close to the original as possible.

Justin------


The Fel-Pro SS72513 valve seal can only be used as a replacement for the integral seal included with the GM #3964264 valve cap. So, one first has to have the 3964264 before the Fel Pro seal can be used. In other words, the Fel Pro seal cannot be used with any other valve cap.

[Kevin B.]

Re: 1966 427/ 390

Many thanks to all who share their knowledge on the board. What I'm facing on this matching number motor (I can't speak to the mileage, as the odometer hasn't worked since the late 70's) is twofold- when I got the car in 1973, it had been rode hard and put up wet, plus it was my daily driver until the mid eighties. Hence the 1980 overhaul. At that time I used the TRW forged pistons spec'ed for the 425 horse motor. These pistons over the years have had the characteristic cold "slap" Lately, though, some light "slap" doesn't go away even after the motor is completely warmed up. Plus, compression with these pistons and the 390 hp head castings is way too high for available fuel, meaning I have to dial back timing to about 4deg initial to have any hope on controlling detonation. I want to at least replace these. Also in 1980, when I magged the rods, (right before we went to install the pistons and found the wrist pins were .003 OS) two rods were cracked at the big end right where the bolt goes through into the cap. I had no spares and due to time and financial pressures I used two "dimple" high horse rods that had been" rebuilt" (ie wrist pin ends dipped in babbit and honed. I would like to get these out of the motor. Again, I really appreciate any knowledge you guys might share!

Justin------


The Fel-Pro SS72513 valve seal can only be used as a replacement for the integral seal included with the GM #3964264 valve cap. So, one first has to have the 3964264 before the Fel Pro seal can be used. In other words, the Fel Pro seal cannot be used with any other valve cap.

[Duke W.]

Re: 1966 427/ 390

Many thanks to all who share their knowledge on the board. What I'm facing on this matching number motor (I can't speak to the mileage, as the odometer hasn't worked since the late 70's) is twofold- when I got the car in 1973, it had been rode hard and put up wet, plus it was my daily driver until the mid eighties. Hence the 1980 overhaul. At that time I used the TRW forged pistons spec'ed for the 425 horse motor. These pistons over the years have had the characteristic cold "slap" Lately, though, some light "slap" doesn't go away even after the motor is completely warmed up. Plus, compression with these pistons and the 390 hp head castings is way too high for available fuel, meaning I have to dial back timing to about 4deg initial to have any hope on controlling detonation. I want to at least replace these. Also in 1980, when I magged the rods, (right before we went to install the pistons and found the wrist pins were .003 OS) two rods were cracked at the big end right where the bolt goes through into the cap. I had no spares and due to time and financial pressures I used two "dimple" high horse rods that had been" rebuilt" (ie wrist pin ends dipped in babbit and honed. I would like to get these out of the motor. Again, I really appreciate any knowledge you guys might share!

Now I understand why you wish to do a full rebuild. The 427/390 is an excellent high performance road engine that has a great blend of low end torque and top end power. The OE cam is close to the small block L-79 cam, certainly closer than to the base small block cam, and the Federal Mogul CS1093M is an exact duplicate that I recommend.

For pistons google Keith Black pistons and look over the hypereutectic catalog for a suitable set that will provide a maximum CR of 10:1.

The rods are not worth saving. I recommend the Eagle SIR5700 for small blocks, and I believe they have an equivalent rod for big blocks that have better durability than the OE rods and are very reasonably priced. For a road engine that is intended for very long service, use a rod designed for pressed pins.

If you want "more power" without affecting low end torque, idle behavior, or visual appearance, head massaging is an option.

If you email me through the TDB I can send you some papers that might aid in your planning effort.

Duke

[Richard M.]

Re: 1966 427/ 390

Does the CS1093M have the machine grooved rear journal as required for 1965(396) and 1966(427) Big Blocks?


Also, won't he need the special rear cam bearing with the groove and the 3 oil holes?

See attached doc from John Hinckley.

I just happened to visit a buddy today and a rebuilt '66 427(from elsewhere), is getting NO oil to the rockers. They discovered the engine re-builder neglected to use the correct grooved rear journal cam and special grooved rear bearing.

Rich

(edit....I just checked my NAPA site and that application is only for the 1967 to 1972 BB's.)
(edit again....There are several cams for the '66 427 and the following note is shown......)

Comments: An Oil Groove Must Be Machined In The Rear Journal;

[Joe L.]

Re: 1966 427/ 390

Many thanks to all who share their knowledge on the board. What I'm facing on this matching number motor (I can't speak to the mileage, as the odometer hasn't worked since the late 70's) is twofold- when I got the car in 1973, it had been rode hard and put up wet, plus it was my daily driver until the mid eighties. Hence the 1980 overhaul. At that time I used the TRW forged pistons spec'ed for the 425 horse motor. These pistons over the years have had the characteristic cold "slap" Lately, though, some light "slap" doesn't go away even after the motor is completely warmed up. Plus, compression with these pistons and the 390 hp head castings is way too high for available fuel, meaning I have to dial back timing to about 4deg initial to have any hope on controlling detonation. I want to at least replace these. Also in 1980, when I magged the rods, (right before we went to install the pistons and found the wrist pins were .003 OS) two rods were cracked at the big end right where the bolt goes through into the cap. I had no spares and due to time and financial pressures I used two "dimple" high horse rods that had been" rebuilt" (ie wrist pin ends dipped in babbit and honed. I would like to get these out of the motor. Again, I really appreciate any knowledge you guys might share!

Kevin-------


Your experience with the forged pistons is EXACTLY the reason that I do not recommend their use for a street engine. I would recommend that you use Keith Black hypereutectic pistons. KB360 will result in a final CR of about 9.5:1; KB176 will result in a final CR of about 10.5:1. I HIGHLY recommend that you go with the KB360 and the 9.5:1 CR. I feel that 9.5:1 is the absolute highest CR I'd use with a big block and I'd prefer even less.

[Joe L.]

Re: 1966 427/ 390

Does the CS1093M have the machine grooved rear journal as required for 1965(396) and 1966(427) Big Blocks?


Also, won't he need the special rear cam bearing with the groove and the 3 oil holes?

See attached doc from John Hinckley.

I just happened to visit a buddy today and a rebuilt '66 427(from elsewhere), is getting NO oil to the rockers. They discovered the engine re-builder neglected to use the correct grooved rear journal cam and special grooved rear bearing.

Rich

(edit....I just checked my NAPA site and that application is only for the 1967 to 1972 BB's.)
(edit again....There are several cams for the '66 427 and the following note is shown......)

Comments: An Oil Groove Must Be Machined In The Rear Journal;

Rich------


Yes, the 1966 block requires that the groove be present in the rear cam journal. If the supplied camshaft is not cut for the groove, one needs to have it done. The rear cam bearing must also have a groove. The correct bearing is supplied with Sealed Power cam bearing set 1255M. The bearing used to be available separately from GM but is long-since discontinued. As far as I know, it's not available separately in the aftermarket.

[Richard F.]

Re: 1966 427/ 390

I am running the good valve springs on my 68 with positive seals. My aluminum heads were machined for the seals. No interference at all. Unfortunately I don't remember the brand of seals as this was back in the 80's. The retainers with the built-in umbrella did not fit.

[Joe L.]

Re: 1966 427/ 390

The retainers with the built-in umbrella did not fit.

Richard-------


I don't understand this, at all. The GM #3964264 valve cap (with integral seal) was supplied as part of the GM #3970627 valve spring unit. The 3964264 was also supplied separately. The 3970627 works perfectly with the 3964264 valve cap. So, if you actually used the 3970627 springs, you should have had absolutely no problem with the 3964264 caps.