Guidance Please? 1967 L71 Engine Reinstall & Run-In

[Richard M.]

I have a big task here and not afraid to ask for help so I don't do something wrong. I have a good experience level with rebuilding small blocks and even rebuilt a few jag V12's myself so I'm not a newbie at this engine stuff by any means, however...... I have never done a bigblock before.

After some paint work to correct improper 80's vintage repairs and incorrect hood stinger placement, the car is back to get the engine work done. The freshly rebuilt 427/435 is ready. I am planning to get it reinstalled, run-in and tested over the next few days, likely ready for initial start on Monday.

I have pretty much everything ready to go. I just got the 3 original carburetors back from the rebuild shop. 3x2 intake manifold is original and in nice shape. 180 thermostat. I have new fuel lines and linkages, etc. Rebuilt original water pump, a nos('06 vintage, non AC top) fuel pump. Engine is stock with no other mods, 0.040" over, original nice '258 TI distributor(with the special groove at the shaft base), my new Napa VC 1765 B26 advance can, repro 263 coil, TI unit with the upgraded solid state module, new M&H engine harness, new M&H TI harness, rebuiilt GM starter, rebuilt original 42 amp alternator, brandy new AC Delco Grp 24 battery, etc, etc.

I am going to modify the center carb for manifold versus ported vacuum as soon as I get the details.

So a few intitial questions......

1- Valve lash - The re-builder data sheet says they did both intake and exhaust to 0.025. I think that's not right. Spec is .023-I /.028-E. Should I reset exhaust lash now cold while it's on the stand? To be safe should I open up the exhaust some more, say .030 or so?

2- This car has Power Steering. However, I'd rather not hook the pump to the system yet. I have to install a new ps valve and piston but do not want to risk a shut down during initial run-in because of a leak etc. Can I fill the PS pump with fluid, block off the hi pressure outlet with a flared plug and block the return? Would this risk damage to the pump?

3- What is the recommended static timing? I've seen various numbers in my readings. I think I know what it should be but would like to confirm.

Thanks,
Rich

[Timothy B.]

Re: Guidance Please? 1967 L71 Engine Reinstall & Run-In

Richard,

I would leave the valve lash alone until after the run in because you will need to do it again anyway, .025 is OK to run the engine.

Running the P/S pump with the pressure line dead headed will open the relief valve inside the pump. I don't think this is good and it will probably get hot. If you can complete the circuit with hoses, supply/return then I think it will be ok. Will the arrangement let it be bolted to the block with the belt off?

Static timing probably 12* but I don't know what the book say's..

[Duke W.]

Re: Guidance Please? 1967 L71 Engine Reinstall & Run-In

I recommend .020/.022" cold clearance using the indexing method in the Hinckley/Williams valve adjusting paper, and I'm assuming you're running an OE cam replacement, like the Federal Mogul CS-165R.

The '65 L-78 specs are .020/.024", but were loosened to .024/.028" for '66 and '67. I dont know why. The '65-'66 cam has the groove in the rear bearing journal. The '67 does not. Other than this the cams are identical - same lobe (used on both sides) and lobe phasing.

The lobe clearance ramp height is .012", so if we assume the rocker ratio is actually 1.7:1 the maximum running clearance should be .012 x 1.7 = .0204".

During normal opeation the valves will not get hot enough to significantly close this up, but sustained WOT will probably heat up the exhaust valve enough to close up the clearance a few thou. GM must have thought so, since they specfied more than the "theoretical" clearance on the exhaust side.

It's valve stem temperature that determines running clearance because the steel pushrod and cast iron block/head expand about the same.

As with small blocks, the rocker ratio is not constant, but starts out a bit low and increases with increasing lift. I've never gotten enough data to nail it down, so until I do, I recommend essentially the '65 spec with a couple of thou off the exhaust side.

The timing specs are in the AMA specs (and should also be in the CSM) that you can download from the GM Heritage site.

Corvette News lists 5 degrees, which you can use for initial run-in, but once you get it broken in I would advance it to the detonation limit or no more than 10 if it doesn't detonate at 5.

The '66 L-72 also has 30 centrifugal, but it comes in a little slower, and the initial timing is speced at 8 with a range of 8-14.

Optimizing the spark advance map, which ilncludes initial timing always comes down the the individual engine, driving conditions, and driving habits. The OE map is a compromise and somewhat conservative to keep the engine out of detonation under worst case conditions.

Check the lash again in the 1000-2000 mile range, and from then on you can go at least 12,000.

Duke

[Michael H.]

Re: Guidance Please? 1967 L71 Engine Reinstall & Run-In

It's valve stem temperature that determines running clearance because the steel pushrod and cast iron block/head expand about the same.


Duke

Yes, the expansion of the valve stem does decrease lash. However, the expansion of the valve head increases lash.

I tried a few settings at less than the engineering recommended .024"/.028" and I wasn't at all happy with the results. Soggy bottom RPM range and nothing new at the top.
I went back to .024"/.028". The engine is very happy at that setting.

Cranky

[Duke W.]

Re: Guidance Please? 1967 L71 Engine Reinstall & Run-In

If the engine is run at WOT for any length of time the valve stems, particularly on the exhaust side, will expand and close up the clearance, which is why mechanical lifter cams have clearance ramps - so the lash won't completely close down and hang the valve open.

Maintenance setting clearances are just the starting point.

Tighter lash slightly increases duration and overlap, which can have an effect on low end torque and idle quality, but if the running clearance is more than actual rocker ratio times lobe clearance ramp height, the valve is being yanked off the seat and slammed back down at greater than clearance ramp velocity, which will accelerate the rate of valve seat recession.

Your choice.

Duke

[Michael H.]

Re: Guidance Please? 1967 L71 Engine Reinstall & Run-In

If the engine is run at WOT for any length of time the valve stems, particularly on the exhaust side, will expand and close up the clearance, which is why mechanical lifter cams have clearance ramps - so the lash won't completely close down and hang the valve open.

Maintenance setting clearances are just the starting point.

Tighter lash slightly increases duration and overlap, which can have an effect on low end torque and idle quality, but if the running clearance is more than actual rocker ratio times lobe clearance ramp height, the valve is being yanked off the seat and slammed back down at greater than clearance ramp velocity, which will accelerate the rate of valve seat recession.



Duke

It's the same for the exhaust valve head too. At WOT, it too increases temp and expands. Because the valve sits on a 45* seat, that expansion automatically increases lash.
I don't remember which has more effect on the lash though, the expansion of the stem or the expansion of the head but eventually one would cancel the other. The valve head dim is a lot smaller than the stem, (expansion per deg/inch) but the head runs a lot hotter. Does it eventually come out even? I don't remember.

Valve lash changes dramatically, both increasing and decreasing during warm up. First, the valve head expands and increases lash. As the stem heats up and expands, it decreases lash.

At that point, with relatively cold heads/block and push rods, the lash may be a bit on the tight side.
As the heads/block and push rods reach operating temp, the lash will be different again.

As far as lash/durability is concerned, I've run solid lifter big blocks at .024"/.028" for many decades and a few hundred thousand miles and I've not experienced any durability issues because of the lash.
My currect car, a 66 425 HP, has been driven all over the country, probably fifty or sixty thousand miles since I built the engine in 1983, and I've had zero issues with the valve train. (new springs/push rods in 83 though)

I tried the recommended 65 only settings on a 65 396 car that I had years ago. The results weren't positive, at all. It sounded faster though.

[Duke W.]

Re: Guidance Please? 1967 L71 Engine Reinstall & Run-In

Many years ago I measured my Duntov cam clearance both stone cold and "hot (idling) and running", and there was no detectable difference, likely because at idle the exhaust valve is relatively cool.

I would suspect that valve stem expanision more than offsets head expansion when the engine is run hard for a net decrease in running clearance, but I have no data.

Other than one exception I recall, everyone who has set clearances to my recommended specs was satisfied. In some cases, a little less low end torque and a little lumpier idle was reported, but all reported that the engine felt smoother, was quieter, and pulled stonger at the top end.

Duke

[Michael H.]

Re: Guidance Please? 1967 L71 Engine Reinstall & Run-In

I would suspect that valve stem expanision more than offsets head expansion when the engine is run hard for a net decrease in running clearance, but I have no data.


Duke

If you have, or have access to a P&G valve gapper, try in interesting experiment. (for those that don't know what a P&G valve gapper is, it's a contraption with a dial indicator that mounts on the valve spring cap and constantly measures valve lash as the engine is running)

Set it up when the engine is cold and watch as the valve lash goes through it's changes. Incredibly, the lash almost immediately opens a few tho, then within a minute or so, it closes up about .003" less than the original setting.
After more and more engine components come up to operating temp, the lash eventually stabilizes.
Seeing three or four tho variation is common.

I have a graph, somewhere around here, that GM did back in about 69. The line (lash) is amazing. At full throttle and high RPM, strange things happen to the lash setting.

I've compared hot/running lash to cold/static lash and I came up with almost .002" on the exhaust side. More on a big block.

[Bill M.]

Re: Guidance Please? 1967 L71 Engine Reinstall & Run-In

I tried the recommended 65 only settings on a 65 396 car that I had years ago. The results weren't positive, at all. It sounded faster though.

Me too. When I first got my '65 L78, I lashed at 20/24. Part throttle response was awful. Going to 24/28 wasn't enough (I don't remember how much it helped). I installed a wide-ratio to go with the 3.55:1...all better.

I remember '69 Z28 (back when new) owners changing axle ratios for the same reason; poor part throttle response.

[Richard M.]

Re: Guidance Please? 1967 L71 Engine Reinstall & Run-In

Need to catch up to all of the info.....thanks guys. We're busy getting prepared to install the engine.....maybe will be in today. I'll check back. Lot's to read and do.

Rich

[Richard M.]

Re: Guidance Please? 1967 L71 Engine Reinstall & Run-In

Update.....Engine installed, getting ready to prep the 2300C for the mods to convert from ported to manifold vacuum. If anyone has photos of the exact mod that would be quite beneficial to me. Pretty busy around here right now......

Thanks,
Rich

[Joe R.]

Re: Guidance Please? 1967 L71 Engine Reinstall & Run-In

Rich,

Strong work! You are moving along quickly. You are blazing a trail for me quite nicely. It appears that you were able to leave the fuel and water pumps on the engine when you installed it. Were any other accessories on the engine at the time of installation?

I will be very curious to see what you find out about converting to full time vacuum. I need to do that, too. I can dig up some previous posts by L71 owners that have done this if that would be helpful.

Joe

[Timothy B.]

Re: Guidance Please? 1967 L71 Engine Reinstall & Run-In

Rich

The drill bits show the path for ported vacuum. You can see the hole in the baseplate bore is above where the throttle blade closes and does not see vacuum until the blade is opened (ported).

Simply drill another 1/16" hole approx where the black dot is between the drill bits thus allowing manifold vacuum to the slot as this new hole is below the throttle blades. You need to put a smear of J&B weld in the ported hole so there is no vacuum leak at curb idle.

Keep this new hole well below the throttle blades like the level of the curb idle hole to the left. The black dot is hard to see, I can take a better pic if you need me too. Try to drill the new hole at the same angle as the ported hole, you will understand when installing a drill bit in the hole.

Thats all there is to it and it's easy to reverse if someone wants to have ported vacuum at idle.

I am not sure what vacuum can the factory used for the engine but make sure the specs of the new VAC allow to be pulled to the stop approx 2" less than idle vacuum.

[Duke W.]

Re: Guidance Please? 1967 L71 Engine Reinstall & Run-In

The OE VAC is the 201 15. Manifold vacuum with the OE cam should be about 14" @900 idling in neutral.

The new VAC should be the 12" B20 or B26 like NAPA VC1765.

Duke

[Richard M.]

Re: Guidance Please? 1967 L71 Engine Reinstall & Run-In

I've finally been able to take a break from the project, and come on over to the Regional at Kissimmee. Arrived last night at about midnight after many long days on the '67 project. We ran into some issues with the install which slowed things down. Much work fitting everything in the engine bay, electrical, etc.

I have decided not to install the TI distributor at this time and use a stock known good points distributor and coil/ballast arrangement for engine run-in. I feel it would be best to not try and troubleshoot a TI problem on a first start. I'll forgo that install until engine is run-in.

As a point of interest the physical engine install went very well. I did not install the transmission prior to engine drop-in, so that went on afterwads. The bellhousing was on the engine for the drop, of course, after transmission test fit on the floor. I did decide to remove the brake MC and booster. MC detached and tie wired to the side and booster removed completely. The only external items on the engine were the fuel pump and water pump, and the intake manifold(no carbs). No oil canister either. There were no major clearance problems, however the throttle lever to foot pedal link was a bit of a problem.(see pic) A little tweeking of the engine to the pass side before lowering it down helped that.

I'm taking a break from the task for a few days and will be at the Regional. Going to see if I can Observe Judge the 67 bigblocks. Should be fun.

Rich