Overheating BBC 468 Pro Street Willy's Coupe

[topradman]

What is idle rpm? Could the idle be high enough that the weak springs are allowing the extra advance and the weights not returning home?
What vacuum can? and only 10 degrees @ the crank is only 5 degrees at the distributor.. sure?
BBC's will tolerate around 52 degrees total @ cruise..
Think I would be around 26-28 degrees initial, 10 degrees max for centrifugal and 12-14 vacuum.. and make sure the vac can unloads when you romp on it so the timing goes back to 34-36 under a good load..

Thanks, I will take all that under advisement and recheck everything and post here. I just ran the engine up to operating temps ( fan on at 185F ) and for the 1st time ever, when I throttle into it to approx. 22-2400 rpm, them temp comes down dramatically and fans shut off. This is with no vacuum can attached and reading now 15 in/hg manifold vacuum. Base is set at 45 btdc and obviously, I can't leave it there but that is at idle, no mechanical involved. The distributor was just curved on a dizzy machine and should be good. Weights are not sticking.

When I lower base timing back to 36 and start throttling into it, the heat starts climbing again when rpm is back up to 22-2400. Put it back on 45 btdc and heat starts going away, especially when I begin to add throttle back up to 22-2400.

I am really beginning to wonder about cam degree being off and/or balancer. At this much timing, engine is still responsive but exhaust note is much quieter than previous. Engine has never seen this much idle vacuum ( 15 in/hg at full engine warm up, idle at about 740 rpm ).

All this is sitting still in the shop in Park. I have not checked what the vacuum advance can do since jacking up the timing this much as I was only getting about 8-9 in/hg previous at idle so about 10 degrees was all that was happening. Now I have some vacuum.

The 52 target all in @ cruise sounds good to me, just need to check balancer mark for accuracy and if ok, may check cam but degreeing in the car will be a time consuming pta for sure!

I am extremely encouraged that any
timing change has brought the temps down, even if it is not a realistic number to leave it at. This at least tells me all the other changes are working and it may be as simple as bad balancer or as pita as cam timing wrong. Of course I will have to reset idle air on carb once this issue is put to bed.

Thoughts?

[topradman]

< I got treed. Was typing while Old posted >

Intake vacuum is good imo. Makes for a cooler running engine, unless the cam is too wild.

I went through the topic but didn't see any advance numbers posted at first glance.

How much initial was the engine running on, during the video for instance?
Seemed like a very low engine vacuum at idle.
Was the vacuum advance connected?

Can you adjust more advance in the vacuum?
How about giving it 20° initial for a try, so it will (safely?) max at around 32° mechanical.
And idle with 30° or more with vacuum connected.

In the video, the base was set @ 16 btdc with vacuum advance unhooked and of course, with port plugged. Idle was about 740 rpm as the video shows.

[Old as Dirt]

My solid roller 496 (271-282 @ .050) has more vacuum at idle than that 468 in the video.. and by the sound on the video, it doesn't sound like that big of a cam..
BTW, MKIV Block/Gen V 088 heads..

[topradman]

My solid roller 496 (271-282 @ .050) has more vacuum at idle than that 468.. and by the sound on the video, it doesn't sound like that big of a cam..
BTW, MKIV Block/Gen V 088 heads..

Agree but cam specs are unknown. A quickie ( was not looking for exact ) dial indicator on the push rod when the valve covers were off (x) the rocker ratio seems to be about 550 valve lift is all and it's a flat tappet hydraulic. With the base timing jacked ahead to 45 btdc ( again, can't leave it there ) the hot idle vacuum goes up to nearly 15 in/hg. Then engine will actually cool down at that point.

This one is a MKIV cylinder head on a Gen V block.

I'm still wondering about possible incorrect cam timing on this engine. Not so much the cam itself but the timing in correlation with the crank.

[Old as Dirt]

Quick check to find a new balancer, and have look at the relationship of the crank keyway to the TDC mark.. at least you would be able to see if the outer ring moved on the hub..
Might also try and jet the carb up a couple of steps richer with the added timing.. Idle mixtures can change from 13:1 with 12deg timing to >18:1 by adding 10-15deg of timing(that is without touching fueling!).

Reference https://www.physicsforums.com/threads/i ... ne.701885/

[rp930]

Shouldn’t be that hard to find tdc.

[Newold1]

Timing that retarded if the timing mark is off that much will definitely cause that engine to run hotter.

Here is a simple old timer method for finding TDC on the engine.

Pretty easy to find TDC on the balancer. Take a sparkplug and weld a short rod -2" into the spark plug body. screw it into #1 cylinder with #1 piston down in the bore, by hand only! Remove all the other plugs and back off all the rockers. Then after installing the checker plug, leave it loose ,carefully bar the engine over until the the #1 piston comes up and lightly touches the plug, loose plug will move slightly to indicate this touch. Mark the balancer with a sharpie marker at this point at the timing pointer. Then bar the engine over backwards until the piston again lightly touches the plug checker. Mark the balancer again at this point at the pointer. Halfway between these two marks will be TDC on the balancer.

[MadBill]

It will really help cooling if the engine gets full vacuum advance at idle; at least 10°, maybe 15°. You could hook it up and then set total idle advance to 45° (X initial plus Y vac.) and go road-testing. If that shows promise, a Crane adjustable VA can is very useful re optimizing mileage and cooling.

[Keith Morganstein]

I keep temp probes in untill the issue is solved.

Recap is that the first temp readings revealed a flow problem. Once the combo of heads and blocks were understood, there were head gaskets availible that might remedy the problem.

At this point it's needed (again) to know temps in and out of the radiator and the block. Otherwise its just more guesswork.