Engine and Transmission Tech

tips, technology, tools and techniques related to vehicle driveline components

Go to Thread: PreviousNext
Go to: Forum ListMessage ListNew TopicLog In
Goto Page: 12Next
Current Page: 1 of 2


Greg55_99
Greg Williams

(98 posts)

Registered:
11/01/2007 07:12PM

Main British Car:


Are cracked blocks safe for reuse?
Posted by: Greg55_99
Date: July 10, 2019 08:04AM

I've seen conflicting into on this and I'd like to get a reading. If a block is leaking behind a liner, is it OK for reuse? I see the Top Hat Turner/Darton sleeves have an o-ring on the bottom to prevent coolant from getting into the crankcase. In theory, the top hat stops coolant from getting in through the top. RPI says "No Way" to any block that's cracked. Any thoughts on this? Is there some definitive tech on this (other than "get a 300").



Edited 1 time(s). Last edit at 07/10/2019 09:34AM by Greg55_99.


ex-tyke
Graham Creswick
Chatham, Ontario, Canada
(1083 posts)

Registered:
10/25/2007 11:17AM

Main British Car:
1976 MGB Ford 302

authors avatar
Re: Are cracked blocks safe for reuse?
Posted by: ex-tyke
Date: July 11, 2019 11:15AM

Don't know why anyone would want use a known cracked block. Thermal cycles will surely make it a ticking timebomb that might leave you stranded.
Do the right thing and replace with a good one.


Greg55_99
Greg Williams

(98 posts)

Registered:
11/01/2007 07:12PM

Main British Car:


Re: Are cracked blocks safe for reuse?
Posted by: Greg55_99
Date: July 11, 2019 12:09PM

If you swing by a boneyard and pick up a Rover V8 block, how do you know it's not cracked?


ex-tyke
Graham Creswick
Chatham, Ontario, Canada
(1083 posts)

Registered:
10/25/2007 11:17AM

Main British Car:
1976 MGB Ford 302

authors avatar
Re: Are cracked blocks safe for reuse?
Posted by: ex-tyke
Date: July 11, 2019 03:06PM

A machine shop would have to use a commercially available 2-part dye penetrant to locate cracks.
The other possibility, depending on the crack location, would be to perform a pressure test.



Edited 1 time(s). Last edit at 07/11/2019 03:14PM by ex-tyke.


minorv8
Jukka Harkola

(168 posts)

Registered:
04/08/2009 06:50AM

Main British Car:
Morris Minor Rover V8

Re: Are cracked blocks safe for reuse?
Posted by: minorv8
Date: July 12, 2019 01:41AM

To do the dye penetrant test properly you need to remove the liners. Sure, you can put the dye in the water galleys but it needs a lot of dye and it will be a nightmare to wash away after testing.

Apparently the pressure test should be done on warm/hot block. Having said that, I made a set of flanges to block the water ways and put 40 psi of air. It has now sat for 2 weeks and there is still pressure inside. How reliable ? Who knows, the block is at ambient temp.


Greg55_99
Greg Williams

(98 posts)

Registered:
11/01/2007 07:12PM

Main British Car:


Re: Are cracked blocks safe for reuse?
Posted by: Greg55_99
Date: July 13, 2019 11:43AM

I get what all of you are saying, but it comes down to my basic question. If you pick up a used block (and they all are now), is it worth sleeving and will it be safe afterwards? There doesn't seem to be much point in picking up a 4.0 or 4.6 if they ALL have a propensity to crack and eventually grenade. It also seems the only "safe" blocks are the Buick 215 or Rover 3.5 blocks.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5812 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Are cracked blocks safe for reuse?
Posted by: BlownMGB-V8
Date: July 14, 2019 11:06AM

I like the 300 iron block. No liner problem, no pulled threads.

Jim



mstemp
Mike Stemp
Calgary, Canada
(199 posts)

Registered:
11/25/2009 07:18AM

Main British Car:
1980 MGB Rover 4.6L

Re: Are cracked blocks safe for reuse?
Posted by: mstemp
Date: July 14, 2019 11:36AM

Jim,

They just are not available in the number that the Rover is for most of us.
Also I feel this block topic is like the Porsche intermediate shaft bearing. Lots of talk but not really all that common in reality. Hope I am not wrong as that is what I have in mine, 4.6L. If it ever fails, I will sleeve it. If block ends up with a crack I will have it welded and sleeved. Man built, man can fix it. U.K. sources offer re sleeved blocks for 2200 GBP, not all that expensive compared to a new LS4 etc.



Edited 1 time(s). Last edit at 07/14/2019 10:30PM by mstemp.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5812 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Are cracked blocks safe for reuse?
Posted by: BlownMGB-V8
Date: July 14, 2019 09:42PM

To each their own Mike. IIRC Buick sold something like 3/4 million 300s so they really aren't all that scarce even today. I realize a few Rover based engines have been built to over 300hp but the block really isn't all that strong. I always had reliability issues with it and I know a lot of other people have too. The iron block otoh has been shown capable of power levels of 1000hp and while I'll never build an engine to that level it's nice to know it is a solid foundation on which to build.

I suspect that was at least part of the appeal of the early SBC. It was a heavy engine, but the block held up very well. The 300, being a high nickel block also happens to be a high mileage engine because it wears more slowly. That in combination with the light weight makes it pretty ideal for an MGB.

Jim


MGBV8
Carl Floyd
Kingsport, TN
(3765 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB, Buick 215

authors avatar
Re: Are cracked blocks safe for reuse?
Posted by: MGBV8
Date: July 17, 2019 12:20PM

I would think that anyone reusing a Rover V8 with a crack behind the liner would have the crack welded before installing new liners.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5812 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Are cracked blocks safe for reuse?
Posted by: BlownMGB-V8
Date: July 19, 2019 09:53AM

Might not be that simple. Welding will distort the casting and it will have to be bored oversized which could complicate things even further. I wonder if a good sealant might not work?

Jim


MGBV8
Carl Floyd
Kingsport, TN
(3765 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB, Buick 215

authors avatar
Re: Are cracked blocks safe for reuse?
Posted by: MGBV8
Date: July 19, 2019 11:00AM

Have to bore it to size anyway for the liner.


Greg55_99
Greg Williams

(98 posts)

Registered:
11/01/2007 07:12PM

Main British Car:


Re: Are cracked blocks safe for reuse?
Posted by: Greg55_99
Date: July 19, 2019 02:02PM

OK, here's another wrinkle. Do the late 3.9l blocks with thick but undrilled mains and caps crack just as the 4.0/4.6L blocks?


MGBV8
Carl Floyd
Kingsport, TN
(3765 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB, Buick 215

authors avatar
Re: Are cracked blocks safe for reuse?
Posted by: MGBV8
Date: July 19, 2019 02:06PM

Any Rover V8 with the 3.7" bore is susceptible to a crack and/or liner slippage. That said, I mostly have only heard about the late blocks cracking.


waterbucket
Philip Waterman
England
(79 posts)

Registered:
07/30/2011 01:08PM

Main British Car:
1978 MGB GT

Re: Are cracked blocks safe for reuse?
Posted by: waterbucket
Date: July 20, 2019 01:48AM

I have always understood that the 3.9/4.0 engines were not that badly affected by cylinder bore cracking whether pre or post cross bolted cranks. The longer stroke 4.6 crank put greater stress on the block aggravating the problem, to overcome this the blocks were ultra sound tested in the factory for wall thickness and colour marked for thin, medium and thick walled bores. 4.6 engines got all the thick walled blocks and some mediums, 4.0 engines got thin and mediums. On that basis the later 4.6 blocks should be better than the earliest ones.
Another factor was in the P38 Range Rover the top hose was the highest part of the cooling system with no air bleed, this led to air locks and overheating. The discovery did not suffer the same problems.
A company in the UK known as Wild Cat Engineering specialises in putting top hat liners in these engines and producing high output engines. The company has recently been sold and is now known as;
[www.automotivecomp.com]
other companies doing the same,
[www.v8developments.co.uk]
[www.johnealesroverv8.co.uk]

I have no affiliation to them but when owned by Ian Richardson were renown for overcoming cracked blocks with top hat liners, no welding was involved, do a google search on "Rover V8 top hat liners" their prices do not look bad either.



MGBV8
Carl Floyd
Kingsport, TN
(3765 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB, Buick 215

authors avatar
Re: Are cracked blocks safe for reuse?
Posted by: MGBV8
Date: July 20, 2019 10:33AM

My understanding is that the problem started when they increased the bore from 3.5" to 3.7", leaving less meat behind the sleeve. Cracks started developing near the bottom of hole for the head studs that were nearest to a sleeve. It was also exasperated by increasing the line bore hole for the larger crank mains that many say were unnecessary. The late Rovers were programmed to run lean & hot for emissions.

I have posted this link before somewhere. I will put it on MGExp, as well.

One reason for failure, if not the main one.

[robisonservice.blogspot.com]


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5812 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Are cracked blocks safe for reuse?
Posted by: BlownMGB-V8
Date: July 20, 2019 10:35AM

Part of the problem is that the engine was designed as a thinwall casting. This was a new development at the time, and while it worked well for iron blocks such as the 300 (especially as the nickel content was increased), the Buick V6 and the 260/289 Ford, Buick was new to the aluminum engine game and did not make adequate allowances for the lower strength material. Because of that, and because of the inherent core shift problems at the time the blocks were both inherently weaker and required cast-in liners to avoid inadequate wall thickness in the cylinder bores. To make matters worse, standard allowances were made for thread engagement lengths and bolt bosses with the result that all of the bolt bores are somewhat substandard, as the cast material does not have the thread pull resistance needed.

Rover made a few changes, which seem to have helped with the thread-pull issue but exacerbated the core shift problems since the liners were no longer permanently bonded in the block. The block itself was reinforced in a few places, all of which added pounds to the weight. But shift forwards a few decades and compare the weight of the Rover block to the Chevy LS1 block, or the block of a Toyota 1UZ and it becomes obvious that there simply isn't enough metal in the block to support moderate to high power levels. It is a marvel of light weight, but it lacks the heft for durability. Although outputs of over 300hp have been achieved, anything over about 240-250 is going to require rapidly increasing levels of investment with accompanyingly decreasing levels of reliability, just the same as any racing engine. It becomes more and more specialized in the weight vs horsepower game, in which it isn't particularly well engineered to compete. By comparison, both the other blocks mentioned above were designed using modern methods with higher rpm and hp targets and the weight is considerably higher. There are good reasons for that. Metal is added in all the critical areas that are required for rigidity and durability. So by comparison the Rover block is neither rigid nor durable. It make no sense to me whatsoever to base a performance build on that block.

By comparison the 300 block which is in the same family also suffers from core shift. Without sonic testing rebores are limited to 0.030"and with only 2 bolts per main bearing, cap walk can be an issue. But it can support power levels up to around 700hp without significant reinforcement and that makes it a more reliable foundation at lower power levels. In the 300hp range it is perfectly happy with any standard rebuild and is renowned for reliability. It is, however, at least 50 lbs heavier than the Rover block. (Or the 1800 that came out of the car.) In the MGB this is not even an issue, particularly in light of the increased torque. If power is your thing, it fares much better in the weight vs horsepower wars. To that you can also add enhanced reliability. It gets beat out by the aluminum LS engines but those are also 50 lbs heavier still, and require surgery to fit into the car while the 300 does not.

So I'm unimpressed with the Rover block, and simply dumfounded by the concept of beginning a build using one that is already flawed. Do you understand why that crack is even there in the first place? It is because of core shift. What is core shift? It's when the location of the sand core that creates the water jacket around the bores has found a less than ideal position during the casting process, with the result that the cylinder wall is thick on one side and thin on the other. When the bores are cut they are not oriented to the centerline of the water jacket, they are aligned with the crankshaft throws and the decks. So when the core is in a less than ideal location (caused by the vagaries of the sand casting process) the wall thickness varies. Get it too thin and you get a crack. The band-aid was to sonic test all blocks and mark them for more or less core shift. You can have that done too, the first step in any SBB build should always be a sonic test.

So welding up the crack is not really much of a remedy and may not even be possible. Certainly boring out a wall that is already too thin doesn't help. For that matter neither is bonding the liner in place, and you can also see why a top-hat liner is not an ideal solution either. You have to also consider that the deck lacks support in that area and will be warped to a greater degree by the pull of the head studs. None of which helps the reliability.

Jim


MGBV8
Carl Floyd
Kingsport, TN
(3765 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB, Buick 215

authors avatar
Re: Are cracked blocks safe for reuse?
Posted by: MGBV8
Date: July 20, 2019 10:41AM

Read my link, Jim.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5812 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: Are cracked blocks safe for reuse?
Posted by: BlownMGB-V8
Date: July 20, 2019 01:14PM

Thanks Carl, I've seen that article in the past. Like most things there are a number of contributing factors. But I still think the root cause is core shift. Why else would Rover mark their blocks as thick and thin? (pink dot preferred) There can be no other cause than core shift. Nothing else could possibly make the cylinder wall vary. The cores are created by standard fixed molds and will not change between being formed and being used. The bore size is constant. However, a dead accurate means of locating the core in the mold was never developed and used during the time those engines were being produced. The methods used by the Brits might have been a little better than domestic at the time but the use of pressed in liners negated any advantage.

Once you understand that it is simple to see how the wall could be thin at the root of one of the head bolt bosses, and the stress and flex from torquing the bolt could pull a crack in the wall. (All materials can flex to some extent. An old mentor advised me that "all metals are plastic" and he wasn't wrong.)

The root cause of course was inadequate engineering. There was no reason that the bolt bosses could not have been extended to the crankshaft web. But again, that goes back to the original design being not quite good enough.

Jim


MGBV8
Carl Floyd
Kingsport, TN
(3765 posts)

Registered:
10/23/2007 11:32PM

Main British Car:
1979 MGB, Buick 215

authors avatar
Re: Are cracked blocks safe for reuse?
Posted by: MGBV8
Date: July 20, 2019 09:13PM

No doubt the cracks are on the thinnest side of the block.
Goto Page: 12Next
Current Page: 1 of 2


Sorry, only registered users may post in this forum.