Ever heard of using " Hard Blok" to repair a severe crack cam tunnel in a 427?

[Georges C.]

Anyone ever used a product called " hard blok" to repair a severely damaged cam tunnel in a big block 427/390 car that has been bored to .70 over? This car will be a street car. I am being told by the seller of the block that it is a common practice for block repairs. However, I've been told by race car owner of an Engine Machine Service company it is only used for racing purposes because it restricts the cooling capacity and should not be used in a street vehicle for daily driving and was never intended as a repair product.

All factual comments would be appreciated.

[Mike M.]

Re: Ever heard of using " Hard Blok" to repair a severe crack cam tunnel in a 427?

pass on it. mike

[Keith B.]

Re: Ever heard of using " Hard Blok" to repair a severe crack cam tunnel in a 427?

Unless it's the born with block I would pass

[Michael F.]

Re: Ever heard of using " Hard Blok" to repair a severe crack cam tunnel in a 427?

listen to mike and keith....pass.

[Joe C.]

Re: Ever heard of using " Hard Blok" to repair a severe crack cam tunnel in a 427?

Anyone ever used a product called " hard blok" to repair a severely damaged cam tunnel in a big block 427/390 car that has been bored to .70 over? This car will be a street car. I am being told by the seller of the block that it is a common practice for block repairs. However, I've been told by race car owner of an Engine Machine Service company it is only used for racing purposes because it restricts the cooling capacity and should not be used in a street vehicle for daily driving and was never intended as a repair product.

All factual comments would be appreciated.

If you fill the block 3/4 ("street" fill) then you will need an oil cooler.
If you fill it higher ("race" fill) then you won't be able to use it for everyday driving as it won't cool at all. Strictly for 1/4 mile runs with cool down time in between.
In any case, filling with Hard Blok requires the bores be honed for extra piston clearance due to extra heat and extra piston expansion.

[Joe L.]

Re: Ever heard of using " Hard Blok" to repair a severe crack cam tunnel in a 427?

Anyone ever used a product called " hard blok" to repair a severely damaged cam tunnel in a big block 427/390 car that has been bored to .70 over? This car will be a street car. I am being told by the seller of the block that it is a common practice for block repairs. However, I've been told by race car owner of an Engine Machine Service company it is only used for racing purposes because it restricts the cooling capacity and should not be used in a street vehicle for daily driving and was never intended as a repair product.

All factual comments would be appreciated.

Georges------


Absolutely out of the question for a street engine. Plus, I don't think the "Hard Block" would be an effective repair for for a cam tunnel crack under any circumstances. In addition, a 0.070 over block is, in my opinion, "used up".

[Chris S.]

Re: Ever heard of using " Hard Blok" to repair a severe crack cam tunnel in a 427?

YES!!!!!!!!!!!!!!!!!!!!!!!!!!!
It works !! and works fine on a street engine
No - you cant fill it up completely like race car engine do....
To rewind - many professional racers use Hard Block - they fill a blocks water jacket to prevent block movement and shift
I have a block that had a crack right along the water jacket
"Bubba" tried to braze the crack - and yes it didnt work
We filled the block just pass the crack -
It worked and worked well
The engine cooling system works just fine - no issues
IT WORKS
I saved an original numbers matching stamped block - and I would do it again in a heartbeat
Chris Sherman

[Patrick B.]

Re: Ever heard of using " Hard Blok" to repair a severe crack cam tunnel in a 427?

It seems reasonable to fill the block to the level of a low crack to save an original block like Chris did, but I can't see how block filler could ever help a cam tunnel. My original 67 427 block had a crack in the lifter gallory area, and it was fixed by furnance brazing. Not cheap but it preserved the original grain and stamping. This is a not the original block, and it would require custom 0.080 oversize pistons at about $700 or more even if it were fixed successfully. Unless the block is a freebe, it is not worth trying to fix.

[Joe C.]

Re: Ever heard of using " Hard Blok" to repair a severe crack cam tunnel in a 427?

YES!!!!!!!!!!!!!!!!!!!!!!!!!!!
It works !! and works fine on a street engine
No - you cant fill it up completely like race car engine do....
To rewind - many professional racers use Hard Block - they fill a blocks water jacket to prevent block movement and shift
I have a block that had a crack right along the water jacket
"Bubba" tried to braze the crack - and yes it didnt work
We filled the block just pass the crack -
It worked and worked well
The engine cooling system works just fine - no issues
IT WORKS
I saved an original numbers matching stamped block - and I would do it again in a heartbeat
Chris Sherman

Did you put an oil temp gauge in that car?

If you had, you would have seen that on the highway, the oil temp would rise to 340 degrees after about 30 minutes of cruising at 65, and stay there until you hit the streets again. If you take your car to the drags, then you'd see that a single pass would raise the oil temp by 30 degrees or more.

I know firsthand how good Hard Blok is. The primary reason for filling a block is to keep the bores rigid under power. Band-aiding a cracked block is not why it's used, although it can and will work for this purpose. But you MUST install an oil cooler.

Don't know whether or not the OP has a breach in the oil galleries as well.

[Chris S.]

Re: Ever heard of using " Hard Blok" to repair a severe crack cam tunnel in a 427?

Did you put an oil temp gauge in that car?

1. No - it is a NCRS Top Flight car - cant have one - but the purpose was to save an orig block - and it did.
2. I am sure there is a fill / no fill point - meaning I am sure there is a point in the water jacket that cant be filled past without creating other issues.
I hope this helps.

[Joe C.]

Re: Ever heard of using " Hard Blok" to repair a severe crack cam tunnel in a 427?

1. No - it is a NCRS Top Flight car - cant have one - but the purpose was to save an orig block - and it did.
2. I am sure there is a fill / no fill point - meaning I am sure there is a point in the water jacket that cant be filled past without creating other issues.
I hope this helps.

That explains it.
Do you still own the car? If you do, you'd best sell it right quick.

[Joe L.]

Re: Ever heard of using " Hard Blok" to repair a severe crack cam tunnel in a 427?

YES!!!!!!!!!!!!!!!!!!!!!!!!!!!
It works !! and works fine on a street engine
No - you cant fill it up completely like race car engine do....
To rewind - many professional racers use Hard Block - they fill a blocks water jacket to prevent block movement and shift
I have a block that had a crack right along the water jacket
"Bubba" tried to braze the crack - and yes it didnt work
We filled the block just pass the crack -
It worked and worked well
The engine cooling system works just fine - no issues
IT WORKS
I saved an original numbers matching stamped block - and I would do it again in a heartbeat
Chris Sherman

Chris------


Whether it works, or not this is a really crazy way to repair a block for a street engine. I would NEVER be comfortable with such a repair. If the car was, basically, never going to be driven, I guess that would be OK. Filling a block's coolant passages is just not appropriate for street engines.

The crack in the lifter valley area, which is fairly common, can be repaired by a methodology known as "stitching" in which special tapered, threaded plugs are installed, each one overlapping the other along the full length of the crack. This repairs the crack and prevents further propagation. It's quite expensive and requires an expert to do it. It would not be worth doing unless the block was especially valuable (e,g. an original block). But, that's the way to do it. Furnace welding, also expensive, can work, too.l

Also, if one has a block that has cracked cylinder walls or at maximum safe overbore, the best plan is to sleeve it. Once again, a very expensive solution and appropriate only for a valuable block (unless all one needs is 1 or 2 sleeves).

[Patrick B.]

Re: Ever heard of using " Hard Blok" to repair a severe crack cam tunnel in a 427?

Our discussion of the importance of not compromising the cooling passages of a street engine may be a little off the topic. Even if one were talking about a drag race engine or an engine strictly for show, how could filling the engine block with Hard Blok do anything to repair a "severely damaged cam tunnel"? Is he talking about trying to fill structural damage with Hard Blok instead of welding, brazing or stitching?

[Joe L.]

Re: Ever heard of using " Hard Blok" to repair a severe crack cam tunnel in a 427?

Our discussion of the importance of not compromising the cooling passages of a street engine may be a little off the topic. Even if one were talking about a drag race engine or an engine strictly for show, how could filling the engine block with Hard Blok do anything to repair a "severely damaged cam tunnel"? Is he talking about trying to fill structural damage with Hard Blok instead of welding, brazing or stitching?

Patrick------


I agree. As I mentioned in my first post I can't see how "Hard Block" would be an effective repair for cam tunnel damage under any circumstances. Depending upon just what this cam tunnel damage is actually like, it might just be that there's no effective way to repair it. For example, if the damage involves "missing pieces", it's a goner. But, in any event, "Hard Block" is not going to repair it.

[Joe C.]

Re: Ever heard of using " Hard Blok" to repair a severe crack cam tunnel in a 427?

1. No - it is a NCRS Top Flight car - cant have one - but the purpose was to save an orig block - and it did.
2. I am sure there is a fill / no fill point - meaning I am sure there is a point in the water jacket that cant be filled past without creating other issues.
I hope this helps.

Better check the oil temp because you've been driving with 340 degree oil.
How long have you been driving that way?
Put a gauge in temporarily, take the car on the highway, and report back what the oil temp is after a few minutes.
If you have been using dino oil, then your pistons and rings are probably badly "coked" if you've been driving this way for awhile.
Thank me later..
Does the NCRS let you install an oil cooler? Hahahahahahahahahaha!