L36 rebuild recommendations

**Joe L.** · June 2, 2006, 07:35 PM

Re: L36 rebuild recommendations

Greg------

It's hard to imagine that with 10,000 miles since rebuild that you'll even need to re-ring it. I would not even bother with that. You seem to imply that you might have a longer milage span on the main and rod bearings. However, if you change your oil and filter regularly, the bearings should be good for at least 100,000 miles. If you want to change them, though, go ahead. They're not too expensive and are not too difficult to replace with the engine in the car. Keep in mind, though, that one of the reasons to change oil and filter regularly is bearing preservation. So, if you just change them at short intervals, you're foregoing one of the benefits that accrue from regular oil and filter changes.

I doubt that you have any problem with the cam bearings requiring replacement. These are usually changed at engine overhaul as a matter of routine but they're often really ok even then. So, I wouldn't be concerned about them unless you have some specific reason to be concerned.

A valve job 10,000 miles ago should be just "hitting its stride". I might replace the valve seals if I had any reason to believe that they needed to be replaced. However, big blocks usually use umbrella or shield type valve seals. These were probably replaced when the valve job was done and I'm quite sure they are still fine. If the engine was converted to positive valve stem seals and the all neporene type were used, you might want to check them.

**Duke W.** · June 2, 2006, 08:44 PM

Re: L36 rebuild recommendations

Yeah, I'm now wondering why Greg wants to get into it.

If you want a little more top end power, Greg, in trade for a little low end torque, just retard the cam four degrees and leave it at that. Idle characterisitics won't change within the range that is normal for L-36.

Duke

**Greg L.** · June 2, 2006, 10:19 PM

Re: L36 rebuild recommendations

I guess it sounds funny that I want to rebuild it again with so few miles since the last time.

The real reason I want to open it up is to replace all the gaskets and seals so I just figured that since I'm in there I might as well change the rings and bearing again.

Even though it doesnt have many miles on it, it's been 17 years so I thought that I had better at least seal it up. Same goes for the transmission. The high clutch pack went on it a couple years after I did the engine so I replaced all the clutches and seals on it at that time. It still worked fine when I took it out but just to be sure I'm going to put in a fresh seal kit.

Duke when you talk of top end power, what rpm are you looking at? This engine only has a 5600 rpm redline and seeing as it's the original one I don't really want to abuse it...doubt it will ever see more than 5000 rpm as long as I have it. If I could get it to pull like a Banshee to 5000 and idle like it was new I'd be happy. Hey it doesn't hurt to dream.

I don't know much about the big blocks reliability but my Dad used to hate them and call them truck engines. He changed his fair share of pistons back in the 60's so I understand his "love" for them so I suppose that is why I'm a little nervous about reving them.

I'm just curious, what can these engines safely rev to?

**Duke W.** · June 3, 2006, 01:19 AM

Re: L36 rebuild recommendations

I think some year L-36/68 were redlined as high as 6000, and I don't think that it's any problem revving them that high as long as they actually produce useable power to that engine speed.

Pocket porting the heads and retarding the cam shifts the torque curve up the rev range, so you have to be willing to rev it high to achieve the gains, but since I don't have an accurate L-36 simulation model or much seat of the pants experience, I don't know what the useable rev limit is.

If you don't feel comfortable revving it over 5000, don't retard the cam.

Revving an engine to the limit is not abuse as long as it's fully warmed up and the oil level is full. "Abuse" is dumping the clutch from a standstill at high revs or WOT and high revs before the engine is fully warmed up.

Big blocks got a bad rap from the early valve spring failures. SBs have a bulletproof valvetrain, but the early 327 rods are weak and prone to failure, especially on high-revving mechanical lifter engines. I don't think BBs other than L-88s that were raced are prone to break rods. In OE trim with later release valve springs the medium performance BBs are pretty reliable as far as I know.

If you feel it needs to be "resealed" then I assume you have some oil leaks. If not, why open it up - just drive it like you stole it.

Duke

**Mark #28455** · June 3, 2006, 11:22 AM

What's your goal?

That's the first question you have to answer. Your prior post mentioned a 1969 L36 so I'm assuming it's a 1969 engine block. The 063 heads are OK, but compared to the later open chamber heads, the flow is a little down. That being said, I would plan on building the engine to maximize your torque below 5600 RPM - shifting the power curve higher in the RPM range is a pain in the rear! Do you want to be able to enjoy the car on frequent drives or do you want to rev it all the time? Revving it gets old really quickly - I have several rectangle port engines and they tend to have soggy low RPM (up to 3000 RPM) performance (but are a blast from 3500 to 6500 RPM).

The factory was actually pretty smart when it came to reliable torquey engines! Unless you are planning to add a stroker crank (which works well in most 1969 blocks), I would leave the short block pretty much totally stock! Keep the "10:1" compression (which in reality is likely closer to 9.5:1) and keep the stock cam too!

If you want more grunt, swap your M21 close ratio trans for the M20 wide ratio gears, it's like swapping your 3.55 for a 3.90 ratio in 1-3 and keeps the same RPM in fourth gear.

You can pocket port your heads if they're apart anyway, but I wouldn't pull it apart just for that. The exhaust ports on the 063 heads have a weak short side radius and to really fix it well usually requires stepping up to a larger valve - BUT I WOULD NOT RECOMMEND THIS for anything other than a true racing engine with headers and an open exhaust.

You can really blow a lot of money very fast by straying too far from a STOCK configuration and end up with a P.I.A. for all your trouble. How do I know? I currently have a fair number of BB engines and each time I took some speed shop's special "secret" advice, I have regretted it later .

The only "trouble free" hot rod modification I would consider would be adding more stroke (the 454 crank with 3/8" rods fits in almost every 1969 427 block and the 4.25 crank is an easy swap, but this requires new pistons and TIME to CHECK all the parts for clearance. So, if your crank and pistons are OK, DON'T BOTHER.

In closing, STOCK IS A GOOD THING !
Mark

**Greg L.** · June 3, 2006, 08:30 PM

Re: What's your goal?

Yes stock is a good thing indeed!

My goal was to get as much power and economy as possible but yet pass a Performance Verification test when the time comes...maybe I'm asking too much! The engine is the original one to the car so I was only looking for minor and undetectable mods. The car is an auto and it will have the stock torque converter in place.

I originaly had thought that there might be a modern version of the old L36 cam...one that idled the same but performed a bit better but seeing as there is not, the original version is what will get installed. I'm still not sure if I should install it straight up or advance or retard it though. I'm not looking to "race" the car so bottom end torque might be the way to go. On the other hand I'm sure that the Goodyear Speedways will have a tough enough time trying to contain the torque in stock form!

As far as the main reason for taking it apart...well...I'm going for a Top Flight with this car so while it's out I wanted to replace all the gaskets and seals. None are dripping but some are weaping so I want to be sure that it is tight before I reassemble the car. The cam also has to come out because it is WAY too big for a stock torque converter. The intake will probably get sent out for re-skining.

So at some point in the near future I'll have a short block on a stand and two complete heads on the bench and figured that if anything should be done to the internals that that would be the time to do it.

It's funny but maybe not doing anything will be the best thing to do.

**Duke W.** · June 3, 2006, 10:54 PM

Re: What's your goal?

With Powerglide, I would certainly not recommend retarding the cam. As OE indexed it is already somewhat "advanced", so leave the indexing as OE production.

Unless the cam is worn, there is no need to replace it.

Duke

**Frank C.** · June 3, 2006, 11:42 PM

Re: L36 rebuild recommendations

Duke...I had always believed that high revving BB disasters were from ununiform valve keepers. I read years ago when Junior Johnson was having valve swallowing problems it was traced to only one keeper doing its job. What da think...Frank

**Duke W.** · June 4, 2006, 01:27 AM

Re: L36 rebuild recommendations

I don't know about the keepers, but the early BB production springs were prone to break.

Clem can probaby fill in more details.

Duke

**Joe L.** · June 4, 2006, 03:15 AM

Re: L36 rebuild recommendations

Duke and Frank-----

Yes, the early springs were definitely prone to break. I went through several on my 1968 Chevelle L-78, and I only had that car for about 18 months (May, 1968 to September, 1969). The old spring number was 3859911. That's the one you don't want to have. Believe it, or not, I've seen guys pay big $$$$ for a set of these on eBay. I hope they want them for "historical reference" and not for use on a car. I wouldn't put a set of these on an engine for "love-nor-money". But, I suppose there are some folks fanatical enough about "originality" that they will.

The GM #3859911 was discontinued from SERVICE in November, 1970 and replaced by the GM #3970627. Actually, the GM #3970627 is not the part number for a spring; it's the part number for a KIT which includes a spring + a cap/seal. The spring, itself, is of an unknown part number, but it's improved over the 3859911. Way improved. It's still available to this very day. It's the one to use. I believe that the PRODUCTION change to the new spring occurred for the 1970 model year. However, some Corvette engines built in very late 1969 (after 1970 engine production had begun for other Chevrolet models) may have had the improved spring.

There were also problems with the valve stem locks ("keepers"). The 65-68 big blocks used lock GM #3747310. This is another piece you don't want to use. It was discontinued from SERVICE in October, 1969 and replaced by the GM #3947880. It was used in PRODUCTION for all 1969 and later big blocks. The 3947880 is still available to this very day.

**Clem Z.** · June 4, 2006, 06:18 AM

310 keys were not hardened and the big

heavy BBC valves pulled right thru them. 880 are hardened so to find which you have on your BBC use a file. GM colored coded the hardened ones for both SBC and BBC and the color that sticks in my mind,as little left as there is these days,was purple and green.

**Joe L.** · June 4, 2006, 11:37 AM

Re: 310 keys were not hardened and the big

clem------

Purple and green were, indeed, the color codes for, respectively, the small block and big block locks. However, that color coding seems to have mostly "gone by the wayside" some time ago. In the last several years I've noted both of these part numbers as being of plain finish or copper plated.

**Clem Z.** · June 4, 2006, 01:12 PM

i guess when all of the other soft keys were out

of the parts system they did not need the colors anymore. i would still use the "file" test to make sure you got the hardened ones

**Greg L.** · June 4, 2006, 07:34 PM

Re: What's your goal?

Actualy the cam is a aftermarket one with a very rough idle so it has to go and the transmission is a THM-400.

L36 rebuild recommendations

L36 rebuild recommendations

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