How can I tell if my longblock rebuild has a "zero retard" cam set without pulling the timing cover? If I have to pull the cover what should I look for? I was told the truck 400s didn't have the retarded cam set and they were only put in automobiles. Since the engine was a longblock rebuild I have no way of knowing what the cam situation is.

 

If this is a rebuilt longblock from the parts store, I guarantee it has a retarded timing set. They rebuild them bone stock to factory specs, and all Ford V8 after about 72 or 73 have retarded timing. I suggest running that motor as bought until the warranty is up, then change the cam and timing set if you like.

Nathan

 

Thanks, Nathan. I bought the truck recently with less than 5k on the rebuild. I have the paperwork on the rework and have to assume it was a "parts store" longblock since it's not clear. Would the performance increase be worth the effort to replace just the sprocket? With the front of the engine open it would be tempting to put in a dual profile RV cam (I use it for towing). I have a source for the cam and lifters for about $150. On a related issue, do you know the stock compression ratio on the 400?

 

farmpaw,

There is no practical way to determine cam timing without removing the front cover to get access to the timing gears.

Nathan is correct about the retarded cam timing in 400s. Starting with MY 1973, all 335 series engines (351C and 400 then) had retarded cam timing, except for the '73-'74 351C 4V engines. All 351M engines (from the beginning of production in MY 1975) had retarded cam timing.

Changing the stock cam to non-retarded timing will improve the low-rpm power some (maybe 5-10%), but it's probably not a worthwhile effort unless you need to get into the front of the engine for something else anyway, say a water pump or leaking front seal. Even then, as you suggested, you'd be better off changing out the stock cam and replacing the timing set to time the aftermarket cam according to the cam manufacturer's specs.

Stock CR on truck 400s was 8.4:1. In '78-'79 car 400s, stock CR was 7.73:1.

BubbaF250

1980 F250 4x4 Custom, 351M/NP435/NP208/D44HD-TTB/D60-FF/3.55s 6750 GVW, Rust & White.

 

So a 1972 351C 4v would not have retarded timing? Thanks...

Tom

 

How does setting cam timing 'straight up' affect your distributor timing?
Should it be advanced or retarded any further?

Thanks!

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1978 F250 4x4 - 351M
Don't crush them, restore them!

 

Since the distributer is driven by (geared from) the cam the distributer timing will have to be reset since it's timed from the crank position.

 

Uh...well sort of. It depends on which timing you're talking about. Certainly the engine could benefit from a better advance curve but the retarded timing being discussed here is between the relative positions of the crankshaft & piston and the opening/closing of the valves. Assuming you install a new "non-retarded" cam & timing set "straight up" you're still going to have to install the distributor in the same relative position to the new cam gear as it was to the old one. The base timing and advance will need to be set for the new assembly but the distributor doesn't necessarily need to be recurved for the new cam.

 

weldman & bill,

I understood weldman's question was about static timing of the distributor. Actually, farmpaw's answer was basically right, even though his explanation wasn't entirely clear.

In essence, cam timing and ignition timing are independent, and both are based on the position of the crankshaft. I think the confusion stems from the fact that the distributor is driven by the camshaft, although distributor timing is based on crankshaft position, and expressed in terms of degrees before or after top dead center (TDC) on the compression stroke.

Changing camshaft timing doesn't necessarily require the distributor's static timing to be changed because the distributor's timing is based on crankshaft position, not camshaft position. (Note: This is independent of any performance considerations that may require different ignition timing, either static timing or advance curves, to optimize the change in camshaft timing.)

Since the distributor is driven by the camshaft, the distributor's position (which determines its static timing) has to be changed to maintain the original distributor timing relative to the crankshaft when you change the camshaft timing. Thus, if you advance the camshaft timing and you don't change the position of the distributor body, the distributor's static timing will be advanced from the timing that was set before you changed the camshaft timing.

BubbaF250

1980 F250 4x4 Custom, 351M/NP435/NP208/D44HD-TTB/D60-FF/3.55s 6750 GVW, Rust & White.

 

bbtkd (Tom),

If the 1972 351C 4V you referred to has the original timing set, the camshaft timing is not retarded.

I believe that Ford did provide some service (replacement) parts for 351C 4V engines that retarded the camshaft timing, though. Many aftermarket suppliers of OEM-type timing sets also provide only the retarded cam timing parts.

So if your engine has had its timing set replaced, it may well have the retarded cam timing.

BubbaF250

1980 F250 4x4 Custom, 351M/NP435/NP208/D44HD-TTB/D60-FF/3.55s 6750 GVW, Rust & White.

 

bubba,

I think we were trying to say the same thing about the distributor timing. Regardless of what cam or timing set used the distributor has to be installed with the crank at TDC on compression so it will vary from stock based on the cam/timing set specs. My concern was distinguishing the base/static timing from the advance curve which theoretically shouldn't have to be changed.

 

Ok, the stock timing on a '78 351M was 8 degrees advanced.
So from what I understand, if the cam and timing gear was put in straight up (when it was originally retarded) the distributor timing would have to be retarded some in order to compensate and make the engine perform efficiently.

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1978 F250 4x4 - 351M
Don't crush them, restore them!

 

weldman,

Yes. If you want to set ignition timing, you have to set it the same way as usual, rotating the distributor body and aligning timing marks with a timing light, regardless of the cam timing.

BubbaF250

1980 F250 4x4 Custom, 351M/NP435/NP208/D44HD-TTB/D60-FF/3.55s 6750 GVW, Rust & White.

 

[font size="1" color="#FF0000"]LAST EDITED ON 25-Aug-01 AT 10:58 AM (EST)[/font][p]Nathan, how do I collect on your guarantee? I bought a pre 71 crank sprocket and gasket set and pulled the front of the engine apart. Guess what? The crank sprocket was identical! Apparently the longblock was put together by someone that knew it was going in a truck. Anyway, it only cost me the cost of the gasket set and about five hours in the engine compartment to determine I won't be getting any more power from that particular direction. For those wondering what they have, the "straight up" crank sprocket has the keyway directly under the timing alignment mark .

 

I'll give you back every dime you paid for my advise! Just send me a self addressed envelope and a $5.00 handling fee and I'll send you a free credit coupon to put towards our next consultation. Thanks for your businessOop

Nathan