# 1966 GTO Pontiac 400 engine problems



## Tyson_M (Mar 15, 2021)

Hello All,

I’m looking for a little insight from some Pontiac guru’s. My dad has a 66’ GTO that is currently torn apart in a local performance shop. It went in for a tune up as we couldn’t get it running right and couldn’t get the timing right. They initially found an oil leak which turned out to be the rear main. They dived further in and pulled the crank out and noticed the crank bearings were scored. The motor had been “rebuilt” and bored to a 409 from a 400. They sent the block to a machine shop and found it was bored over size and were surprised it even had compression. I don’t know the specific numbers as of right now because the shop and I are in a bit of an argument as he wants to scrap the motor and go with an LS swap (quoted 25k) but we would like to just keep it all Pontiac. Not trying to build a race car. Also someone had welded on the crank, I’m assuming for balancing and it created spider cracks and we are told it’s no good. So my question for the Pontiac guys is, would you guys go the route of buying a new block and boring the cylinders to accommodate the pistons we have now as they are still good and find a new 400 crank which seem impossible to find. Or would you guys suggest we scrap the motor and build something fresh either another 400 or maybe even a 389.Another question, does a 400 crank need to be out of the 400 or can you use/modify a crank from a Pontiac 350. I would appreciate any input, I feel like we are in over our heads and the shop has us right where they want us.

thanks guys!


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## Jared (Apr 19, 2013)

If your block has already been bored once, you may not be able to do it again for a second rebuild depending on how much material was taken off the first time. A crank with visible cracks is a ticking time bomb. They do break and the carnage can be pretty bad (ask me how I know). I wouldn't go through all of this to reuse just the pistons. A Pontiac build will be expensive but should cost you WAY less than the $25K your shop quoted you for the LS swap. Downside is there are not a lot of shops that build Pontiac engines and supply the core. The one's that are out there have lengthy backlogs. for comparison, mine blew up last June. The short block was finished and arrived just before the holidays and I just got the heads last Friday.

Side note. I'd come to an agreement on what you owe for the work up to now and find a different shop or a buddy to help. Engine installs on these old cars is really not that hard.


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## Lemans guy (Oct 14, 2014)

I don't know where you are, but talk to a builder like Butler Performance Pontiac in Tennessee. They build the engines and supply the blocks. they are not cheapbut have various prices you can explore. Sure there is a wait time. but you might gain some info. I would get my stuff and square with these guys early. They seem like they are selling you something that you don't really want.


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## BearGFR (Aug 25, 2008)

How much has it been bored? That's a key question. Cranks aren't hard to get at all, if you go aftermarket. If it were me, I'd go pay that shop whatever I owed them, collect all my parts, and go find a shop that actually knows something besides "LS swap the world". 
You can get a stroker kit from Butler Performance that's complete with a new crank, forged rods, and pistons that would pretty much be a drop-in deal. First though, you need to know what the bore size is right now. Stock 400 is 4.120. 

Bear


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## Lemans guy (Oct 14, 2014)

https://butlerperformance.com/i-31643271-butler-pontiac-performance-crate-engine-461-474-cu-in-turn-key.html?ref=category:1267471



Here is one beautiful butler engine for this price.....they are cheaper ways. But find out what is out there


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## ylwgto (Oct 27, 2009)

I don't know where you are, but I bought a rear end from the guy that posted the ad below. If local, seems like a decent deal on a documented/blueprinted rebuild with trippower. I did not see the engine, but did see the machine shop paperwork and blueprint specs...was thinking about making an offer on it myself.









1968 Pontiac GTO 400 Engine - auto parts - by owner - vehicle...


Rebuilt 1968 pontiac 400 Tri-power Engine Block code ( YS ) Head casting ( 62) Blue printed / Balanced Have documentation $6000 Aluminum Radiator $300 New 700r from monster transmissions With...



monterey.craigslist.org





Good luck!


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## PontiacJim (Dec 29, 2012)

Collect your engine parts and move on. The machine shop is not helping you and apparently is not too interested in doing so if he is recommending an LS swap.

The Pontiac block can go, .030" & .040" over without issue. It can go .060" depending on the year of the block - very important. Some blocks, the later ones, can have thinner cylinders and it is still best to check cylinder wall thickness when going up to .060" on the overbore. If already .060", then the block is not worth using at this point unless a light honing can clean up the bores and new .060" pistons used. So pistons can be had in almost any size bore IF going after market custom pistons such as Ross pistons through Butler Performance. But wait, there is more before you get scared on pricing.

Check out the 400CI stroker kits. These include new crank, new rods, new pistons (which you can order in custom sizes and valve relief CC's to get compression down), new rings/bearings, and the assembly is balanced. Best bang for the buck. You can then keep the Pontiac a Pontiac powered car instead of a Beaumont. You also won't have to change wiring, fuel lines, trans, gas tank w/electric pump, exhaust, etc..

That said, not knowing if you have an alternative machine shop that you can take the engine to, I would pay the machine shop for their services and collect my engine. If you have to use the shop, then stand firm your ground ad tell the shop what you want - YOU are paying them for their services, not the other way around. YOU are the boss as to what you want for your engine/car, not the shop. If they can't do as you request, again, find another builder.


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## LATECH (Jul 18, 2018)

I have a virgin 400 block in very good shape if interested.
I am north central Pa, south of mansfield a few miles


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## Mine'sa66 (Oct 30, 2019)

I vote keep it Poncho.
If you want an LS, there's plenty of Camaros and Corvettes out there.
These guys seem interesting...


Len Williams Auto Machine


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## michaelfind (Dec 14, 2018)

Ditto what all these eight posters ahead of me just said. Butler did a great job for me and they will talk to you without telling you what to do with your car or motor. I hear very good things about Len Williams too. Some buddies and I may take three motors up to him this summer. Maybe you should get in line before we keep him busy for the rest of the year😄


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## Tyson_M (Mar 15, 2021)

Thank you guys for all the input! Big issue we were having is we are in Canada and it is very hard to get stuff here right now. Ironically enough the shop had called my dad yesterday letting him know they brought in a new block and crank which will cost 400 bucks CAD. The block is apparently a factory 400. I’m hoping the crank is the right one as I’ve read they are fairly specific. I was about to arrange to settle up what was owed and start from scratch but now that they brought in a block and crank that kind of changes things. They said they plan to bore the cylinders to match the pistons we have which were “supposedly” brand new. Now from some of your guys input, I feel hesitant to reuse anything from this original engine. They claim the top end parts are all good. Last thing we want to do is make this car more of a headache and start to resent it for how much money/problems it’s costing. These cars are suppose to put a smile on your face haha. As far as money goes we will be into this motor if we continue with this route around 8k. Now the question is should we spend a little more money and go with one of these stroker kits mentioned. I really appreciate all the advice, it’s cool there are groups of people out there like this!


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## clasoftx (Jul 25, 2018)

Tyson_M said:


> Hello All,
> 
> I’m looking for a little insight from some Pontiac guru’s. My dad has a 66’ GTO that is currently torn apart in a local performance shop. It went in for a tune up as we couldn’t get it running right and couldn’t get the timing right. They initially found an oil leak which turned out to be the rear main. They dived further in and pulled the crank out and noticed the crank bearings were scored. The motor had been “rebuilt” and bored to a 409 from a 400. They sent the block to a machine shop and found it was bored over size and were surprised it even had compression. I don’t know the specific numbers as of right now because the shop and I are in a bit of an argument as he wants to scrap the motor and go with an LS swap (quoted 25k) but we would like to just keep it all Pontiac. Not trying to build a race car. Also someone had welded on the crank, I’m assuming for balancing and it created spider cracks and we are told it’s no good. So my question for the Pontiac guys is, would you guys go the route of buying a new block and boring the cylinders to accommodate the pistons we have now as they are still good and find a new 400 crank which seem impossible to find. Or would you guys suggest we scrap the motor and build something fresh either another 400 or maybe even a 389.Another question, does a 400 crank need to be out of the 400 or can you use/modify a crank from a Pontiac 350. I would appreciate any input, I feel like we are in over our heads and the shop has us right where they want us.
> 
> ...





Tyson_M said:


> Hello All,
> 
> I’m looking for a little insight from some Pontiac guru’s. My dad has a 66’ GTO that is currently torn apart in a local performance shop. It went in for a tune up as we couldn’t get it running right and couldn’t get the timing right. They initially found an oil leak which turned out to be the rear main. They dived further in and pulled the crank out and noticed the crank bearings were scored. The motor had been “rebuilt” and bored to a 409 from a 400. They sent the block to a machine shop and found it was bored over size and were surprised it even had compression. I don’t know the specific numbers as of right now because the shop and I are in a bit of an argument as he wants to scrap the motor and go with an LS swap (quoted 25k) but we would like to just keep it all Pontiac. Not trying to build a race car. Also someone had welded on the crank, I’m assuming for balancing and it created spider cracks and we are told it’s no good. So my question for the Pontiac guys is, would you guys go the route of buying a new block and boring the cylinders to accommodate the pistons we have now as they are still good and find a new 400 crank which seem impossible to find. Or would you guys suggest we scrap the motor and build something fresh either another 400 or maybe even a 389.Another question, does a 400 crank need to be out of the 400 or can you use/modify a crank from a Pontiac 350. I would appreciate any input, I feel like we are in over our heads and the shop has us right where they want us.
> 
> ...


I have gotten 2 Pontiac motors from Len Williams in Bristow, OK.
455 and 400, both are very streetable. My 455 rebuilt and my 400 purchased outright, no core. His number if you want to talk to him 918-352-9711. He has been around o long time building Pontiacs. He also has a web page


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## jedi (May 18, 2016)

Hi Tyson,

I live in Western Canada, just wondering where you are located

Jim


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## 4rd4fun (Oct 24, 2019)

what about blue print engines- not sure what they offer but they are here in my little town, they seem to have good customer service. Maybe they don't sell Pontiac? BluePrint Engines - Crate Engine Manufacturer


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## gtoguy4 (Feb 6, 2015)

Tyson_M said:


> Hello All,
> 
> I’m looking for a little insight from some Pontiac guru’s. My dad has a 66’ GTO that is currently torn apart in a local performance shop. It went in for a tune up as we couldn’t get it running right and couldn’t get the timing right. They initially found an oil leak which turned out to be the rear main. They dived further in and pulled the crank out and noticed the crank bearings were scored. The motor had been “rebuilt” and bored to a 409 from a 400. They sent the block to a machine shop and found it was bored over size and were surprised it even had compression. I don’t know the specific numbers as of right now because the shop and I are in a bit of an argument as he wants to scrap the motor and go with an LS swap (quoted 25k) but we would like to just keep it all Pontiac. Not trying to build a race car. Also someone had welded on the crank, I’m assuming for balancing and it created spider cracks and we are told it’s no good. So my question for the Pontiac guys is, would you guys go the route of buying a new block and boring the cylinders to accommodate the pistons we have now as they are still good and find a new 400 crank which seem impossible to find. Or would you guys suggest we scrap the motor and build something fresh either another 400 or maybe even a 389.Another question, does a 400 crank need to be out of the 400 or can you use/modify a crank from a Pontiac 350. I would appreciate any input, I feel like we are in over our heads and the shop has us right where they want us.
> 
> ...


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## gtoguy4 (Feb 6, 2015)

I have a 1966 GTO engine sitting in my garage. It was rebuilt many years ago by Reid's Automotive in Whitman Ma. I never had occasion to use it. If you're interested, and make an offer, plus pay for delivery, I might sell it. All my GTOs have good running engines, and I don't foresee any use for it in the future. J.M. 508-776-2088


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## XceedVne (Aug 16, 2019)

Another vote on keeping it Pontiac. There are tons of guys out there building Pontiac motors pan to carb. Drop in and go. Get to keep all your accessories and brackets. Butler is the top of the list but there are builders out there with a decent reputation selling for less. Ebay has lots of "Crate" 400's and 455's. I would stay with the 400 and just bolt everything back on. Easiest solution, and a great option. Just find out weather you have 8 or 11 bolt water pump as I believe there is an issue with the pully depth being different. I think gtoguy4 may have a great solution.


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## Jared (Apr 19, 2013)

clasoftx said:


> I have gotten 2 Pontiac motors from Len Williams in Bristow, OK.
> 455 and 400, both are very streetable. My 455 rebuilt and my 400 purchased outright, no core. His number if you want to talk to him 918-352-9711. He has been around o long time building Pontiacs. He also has a web page


I bought a LW 455 short block for mine. It's still wrapped in plastic waiting to be assembled. The machine work on it looks really good. I placed the order with him in late June/early July and the engine showed up at my door the week before Christmas. When I talked with him in October, he said his shop got REALLY busy since the pandemic hit. There are a couple other members on here that have engines on order with him and the back log is long. That being said, I based on what showed up, I wouldn't hesitate to work through him again. Other note is I had reached out to Butler before Len Williams and they told me that their lead time for an assembled engine was at least a year. My guess is it is longer now. Personally, the wait didn't bother me. I would rather deal with a busy shop than one that is waiting for my work to have something to do. A busy shop speaks to it's reputation and usually the quality of work.

I would recommend using the 400 block the OP's shop found and buying a complete rotating assembly through Butler. Without knowing anything about the crank shaft they have, I would be very hesitant to use it. Butler balances the assemblies before they ship them so there is no additional work for the builder after the block is cleaned up. Just make sure to order the correct pistons for the bore size and heads to hit a pump friendly compression ratio. If your heads are good use them. Definitely replace the cam and lifters.

Good luck and try to have fun with it.


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## Jared (Apr 19, 2013)

Sorry, just re-read that. The LW short block comes assembled. It is waiting for me to install the oil pump and put the top end back together.


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## Scott06 (May 6, 2020)

Glad to see the shop is more willing to help you that do the LS. One comment on the block - if it is the original date code correct 389 for your 66- you should look into sleeving it if the bore is the only issue. If its a later 400 replacement just get another block. 

On the crank and rods you should look into a new crank and rods from eagle or similar. Ive been impressed with the affordability of these vs remachining older weaker crank and rods. Paul Spotts of spotts performance sells crank and rods kits. In additon to butler I have found him to be an invaluable technical resource. Like the others he has a year wait for an engine but any parts Ive ordered have shipped very quickly.


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## Docpontiac (Mar 6, 2021)

Tyson_M said:


> Hello All,
> 
> I’m looking for a little insight from some Pontiac guru’s. My dad has a 66’ GTO that is currently torn apart in a local performance shop. It went in for a tune up as we couldn’t get it running right and couldn’t get the timing right. They initially found an oil leak which turned out to be the rear main. They dived further in and pulled the crank out and noticed the crank bearings were scored. The motor had been “rebuilt” and bored to a 409 from a 400. They sent the block to a machine shop and found it was bored over size and were surprised it even had compression. I don’t know the specific numbers as of right now because the shop and I are in a bit of an argument as he wants to scrap the motor and go with an LS swap (quoted 25k) but we would like to just keep it all Pontiac. Not trying to build a race car. Also someone had welded on the crank, I’m assuming for balancing and it created spider cracks and we are told it’s no good. So my question for the Pontiac guys is, would you guys go the route of buying a new block and boring the cylinders to accommodate the pistons we have now as they are still good and find a new 400 crank which seem impossible to find. Or would you guys suggest we scrap the motor and build something fresh either another 400 or maybe even a 389.Another question, does a 400 crank need to be out of the 400 or can you use/modify a crank from a Pontiac 350. I would appreciate any input, I feel like we are in over our heads and the shop has us right where they want us.
> 
> ...


It’s


Tyson_M said:


> Hello All,
> 
> I’m looking for a little insight from some Pontiac guru’s. My dad has a 66’ GTO that is currently torn apart in a local performance shop. It went in for a tune up as we couldn’t get it running right and couldn’t get the timing right. They initially found an oil leak which turned out to be the rear main. They dived further in and pulled the crank out and noticed the crank bearings were scored. The motor had been “rebuilt” and bored to a 409 from a 400. They sent the block to a machine shop and found it was bored over size and were surprised it even had compression. I don’t know the specific numbers as of right now because the shop and I are in a bit of an argument as he wants to scrap the motor and go with an LS swap (quoted 25k) but we would like to just keep it all Pontiac. Not trying to build a race car. Also someone had welded on the crank, I’m assuming for balancing and it created spider cracks and we are told it’s no good. So my question for the Pontiac guys is, would you guys go the route of buying a new block and boring the cylinders to accommodate the pistons we have now as they are still good and find a new 400 crank which seem impossible to find. Or would you guys suggest we scrap the motor and build something fresh either another 400 or maybe even a 389.Another question, does a 400 crank need to be out of the 400 or can you use/modify a crank from a Pontiac 350. I would appreciate any input, I feel like we are in over our heads and the shop has us right where they want us.
> 
> ...


It’s a 66 go back to a 389 if you can but if you can’t 400 is a good bet. Buy a short block from Butler there the best. Don’t go the LS way too many GTOs have lost ther Pontiacness and just became chevelles with Pontiac sheetmetal! Was it a 4 bolt main or 2 bolt mains? Or start a search for a 67-69 bonneville with a 428 ci ! Don’t go 455 boat an anker. 
Good luck


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## PontiacJim (Dec 29, 2012)

Tyson_M said:


> Thank you guys for all the input! Big issue we were having is we are in Canada and it is very hard to get stuff here right now. Ironically enough the shop had called my dad yesterday letting him know they brought in a new block and crank which will cost 400 bucks CAD. The block is apparently a factory 400. I’m hoping the crank is the right one as I’ve read they are fairly specific. I was about to arrange to settle up what was owed and start from scratch but now that they brought in a block and crank that kind of changes things. They said they plan to bore the cylinders to match the pistons we have which were “supposedly” brand new. Now from some of your guys input, I feel hesitant to reuse anything from this original engine. They claim the top end parts are all good. Last thing we want to do is make this car more of a headache and start to resent it for how much money/problems it’s costing. These cars are suppose to put a smile on your face haha. As far as money goes we will be into this motor if we continue with this route around 8k. Now the question is should we spend a little more money and go with one of these stroker kits mentioned. I really appreciate all the advice, it’s cool there are groups of people out there like this!


I am assuming the 8K in the engine is including the previous rebuild, and not what the machine shop is charging you presently.

I think you are in a tough spot in choosing what route to go - if you already have 8K into the previous build plus what you have into it now. If you continue to do upgrades, ie stroker, you are going to end up with a really $expensive engine that you may have gotten a better value in purchasing a turn-key engine from a Pontiac engine builder.

What is the top end? Iron heads? Aluminum heads? Roller cam/lifters? Aluminum intake/Holley carb? 

If the shop says you can re-use the almost new pistons, then they know what is good or bad and if they used "bad" pistons, both their reputation and $rework they will have to do is not something they would chance. Can you re-use pistons? Certainly, have done it myself on assorted engines.

As pointed out earlier, what is the bore size? I have to assume .030" because they are going with the near new pistons and would not favor a piston that was .060" over and would have told you you needed pistons. So boring the supplied 400 block they got for you should be good. A shop has to have pistons in hand to bore/finish hone the block. STAY away from the later 1975 and up blocks, especially the "557" casting. These are weak and should not really be used unless going low performance. The later blocks found in the Trans-Am's can be used as they were cast heavier and have an earleir casting number to ID as well as "XX" cast on them in the lifter galley.

The crank is not that specific. There is small main journal and big main journal cranks which is the BIG difference. Rod journals are the same for both. The small journal, as the 400 has, fits blocks, 400CI and under. The 421, 428, 455CI is the large journal and specific to these blocks. So again, should not be an issue. The only thing you want to check is to ensure the back of the crank has the hole drilled in it for the pilot bearing IF using a manual transmission. Some, not all, are not always drilled for a manual trans because an automatic does not need this step. Very few are not drilled, but you want to check if a manual trans is used.

You are going to want to have the rotating assembly balanced, even if this was already done to ensure all is well. You did not mention if the engine has cast or aftermarket forged rods? If they are factory cast rods, now is the time to change these out for a set of stronger/new forged rods. You can get a set of inexpensive forged I-beams which is fine for most stock/high performance builds unless you have big HP or plan on turning over 6,000 RPM's with the engine. If so, then you can step up to the H-beam rods which are more money. You want to do this before balancing, this is why I mention it.

Other upgrades to see if your engine already has this is: threaded pipe plugs in the front oil galley in the block to replace the factory style pressed in oil cups that get staked in place. Simple upgrade your shop should know about and easily do. Just make sure they are not inserted/threaded too deep and cut off oil supply.

Make sure you have an upgraded aftermarket oil pump drive to replace the tired/weaker factory drive. This is usually upgraded on most rebuilds, so you may already have one.

Make sure you have the 60PSI oil pump and not a 40 PSI oil pump (low performance engine use). Mellings seems to be the most common and most will get the 60 PSI pump which the GTO and high performance Pontiac engines used. Do not use the 80PSI pump. I went with the Butler 60 PSI Pro-Oil pump because it is a blueprinted Mellings pump and has a thicker bottom plate with anti-cavitation slots and flows more GPM, not more pressure. Same as stock, but better, so no issues with engine/pan fit.

Use the Best brand graphite rear main seal versus the supplied rope seal or aftermarket Viton rear main seal. Seems most have no problems with this seal, whereas they do with the other two.


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