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Discussion Starter #1
Gentlemen,

I have a Superformance Cobra with an Alum. 460 that has approx. 25k miles on it. I believe it needs rings as it consumes more than a little oil (maybe a quart every 300m?)
What are your thoughts on a re-ring only? (I shudder as I write that, please be kind!) The oil pressure looks good (80 psi @ idle cold, 60 idle warm, 80 warm @ 2k)
I would hate to re-build the bottom end if every thing is tight and in good condition.
I would also like to change the cam to a roller. Not a huge one, just looking to free up some power and loose the friction of the solid tappet.
Please look at my set-up and comment.
Thanks for looking & commenting
Jason

Block Ford Motorsports/RDI Aluminum A96
Bore 4.390
Stroke 3.850
Pistons Wiseco, forged 10.48-1
Rods Eagle, ESP H-beam 6.605
Crank Ford
Oil Pan Aviaid 9 quart Road race w/ Accusump
Oil pump Melling M-84DHV
Water pump Ford Aluminum
Cam Comp Cams flat tappet, 34-342-4 (294/294 adv, 248/[email protected] .605 lift, 110 L/C)
Heads Alum Cobra-Jet, ported @ Olthoff Racing(?)
Rocker arms Ford Motorsports rollers 1.73
Push rods (?)
Intake Edelbrock Torker II
Carb Barry Grant Race Demon 825 Road race
Fuel pump Mallory 4110
Ignition Ford Motorsports B-12199-B301
Distributor MSD Billet
Header 2” Primary
Sidepipe 2 1/4
Flywheel McLeod Aluminum
Clutch 12” McLeod Diaphragm
Trans Tremec TKO (.68 5TH )
Gears Ford Motorsports 4.10
 

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Rings

There is absolutely nothing wrong with re-ringing if everything else looks OK as far as cylinder finish, etc. Just make sure that you hit everything that could be causing the oil consumption - guides, seals, etc. Might not be a bad idea to check rod clearance and side clearance......
 

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Hi
I'm not sure how your set up is on the corbra's but is the oil filter to close to the headers.. causing it to super heat the oil?? I know the filter is up front but how tight is the motor compartment?? I can't imangen at only 25K miles it needs to be ringed. but I don't know about those aluminum blocks?? or how hard it was dirven. Does it smoke a lot?? I'd run a compression test and maybe a leak down befor I'd ring it.. Seams like the oil prusher is good, might just be valve giudes seals.. are you getting alot of blow by??
I just thought of something else could the PCV be sucking oil in are the baffels OK in the valve covers?? pull the pcv hose at the carb end and see if its oil soaked?
hope you get it figgured out..
tim
 

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25 miles seems to me too soon to determine very much. Your smoke, if that is what it is- could be coming from the vac line to a leaky vac modulator, lack of baffles by the PCV valve, etc- I would be looking for every other (easier and cheaper!) source I could imagine before tearing something down.
 

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HI again
Now I have another idea
Maybe the HV pump is filling up the valve covers and you sucking oil in the PCV like I posted earlyer. Maybe the drain back holes in the block and head need ported a little to let more of the oil to return to the pan.
Thats a prob I have heard from some people that run a HV pumps..
tim
 

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Before you tear down the engine try changing valve stem seals. Use a positive seal neoprene type and not the teflon seals that most alum. heads come with. My experence is I reduced oil consumption from a quart every 3-400 miles to a quart every 1000-1100 miles by changing only the v/s seals. Theory is the oil is being sucked up past the guide o/d and not down the valve stem. Worth a try and about an hour to 2 hours worth of work before you go to the trouble to pull the engine and tear it down.
 

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Discussion Starter #7
Thanks for the feedback guys,

The valve guides and seals were replaced about 5k miles ago, the oil drain back holes have been opened up and it does not have a PCV. The oil filter is a remote, mounted in the radiator air stream, and it has an oil cooler (traditional Cobra type Mocal up front).
With regards to smoke, it will leave a light haze the first time you hammer it. After that its clean.

If the rings are worn, shouldn’t I see blow by out the valve cover breathers?
 

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If it was burning a quart every 300 it should be smoking like mad. Since it's not, I would still be suspicious of the valves seals. Was oil consumption the reason the seals were replaced?

Brad
 

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25K , as in 25,000 miles ? If so , that kind of miles with an aluminium block and a racey pistons 300 miles to a qt is not a big deal , but it could use rings IMO . If the power is still good i'd vote to buy a case of oil .
 

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Discussion Starter #10
Brad,
Yes, the seals were replaced because of the oil consumption. I agree that it should be smoking!

Lem,
Yes 25000 miles, Power is good So I shouldnt be concerned, just top it off and drive the piss out it?
 

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My point is that , long term , the rings will not hook up as good in the A96 block as one of the iron race blocks . Also , the better pistons need more piston to wall which could effect ring seal term .
It should be considered that after a rehone , that the piston to wall would be greater and ring seal would go away quicker than ever .
If you have no loss of power and no spark plug fouling , you may use the money to put a 4.150" crank and an over bore in your next redo ! Then you could really scare others and/or your self with that monster !!!
 

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Discussion Starter #13
Lem,

Why 4.150? (I was thinking 4.500)
What would you estimate te cost of the stroked rebuild?

Brad,

The motor was originally assembled by Olthoff racing in N.C. IN 1999
 

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If you do not like the oil consumption , with the stock stroke , after 25,000 miles you sure will not like it with the 4.500" stroke .
That 1st .300" of extra stroke put in an engine will be the biggest gain in performance you will get , IMO .
 

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Hmmm, Olthoff has been around a while. There shouldn't be an assembly issue with them at the wrenches. Even so, I'd be tempted to give them a ring and tell them your problem. If nothing else, maybe they can give you some direction.

Lem, I question your statement about the longer stroke being associated with oil consumption problems. In a properly assembled and broken-in street engine stroke lenth should have no significant effect on oil consumption.

Also, overbore engines definitely have a place in racing where piston speeds are an issue, but the effect on most street machines is so negligible as to be nearly irrelevant. For most builds the time and money spent tweaking bore/stroke ratios could be spent more effectively on something else.

Brad
 

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Very long strokes load the cyl wall more . More load equals more wear which effects ring seal . Properly assembled goes without saying...I did not say from the 1st day....at 25,000 miles .
 

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True, but the loading difference in going from 4.150 to 4.5 on an engine turning 6K or less should be minimal. That's only about an 8% change in rod length. IIRC the change in side loading is not linear to the change in ratio, rather it's a percentage of the change based on RPM (can't remember what the formula is). The 8% change in rod length on a mild-to-moderate street mill should only result in a few percent difference in side loads.

Of course, I'm doing this all by memory, so... :mrgreen:

Brad
 

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Discussion Starter #19
Ok I bought some oil.

What do you guys think its going to cost me to rebuild?

Bore to 4.5 - 4.6
req'd block machining
steel crank 4.15 -4.50
rods 6.8?
pitons 11 to 1
balance
assemble
 
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