Engine and Transmission Tech

Hi folks,

I have a 4.6L Rover THOR-intake V8 pulled from a 2004 Discovery sitting on an engine stand in my garage, and a burning desire to drop it into an MGB. It's a sick patient though, and I could really use some guidance and suggestions as to how to proceed.

I'm new to engine teardowns and rebuilds, but I've read Roger Williams' How to give your MGB V8 Power, I just started reading Tom Monroe's Engine Builder's Handbook, and I have a pdf of the Rover factory rebuild manual for the 4.0/4.6.

I bought the engine for a song (caveat emptor and all that), and I'm happy if this engine turns out to be a boat anchor. I needed something to get my hands on, and the $250 price tag was right. I can always sell the useful parts to recover my expenses if I have to.

I'd like to make a rational assessment of whether this engine is worth rebuilding to a mildly tuned state, or whether I should move on to another block. My preference is to keep costs low, to get my V8 MGB built, and to return to the engine for a major rebuild and upgrades down the road.

Here's what I know:

The engine has approx. 125,000 miles on it.

I bought it from a mechanic who parts out cars on the side. This particular Discovery came into his shop, and the owner didn't want to make further attempts to repair the engine after one failed attempt, and abandoned the entire truck. The water pump, alternator, AC compressor, crankshaft pulley/harmonic balancer, coil packs, and starter were removed and sold to other buyers before I showed up. I never saw the engine in the truck, and I never heard it run.

I was told the shop tried to repair a "blown head gasket," but the repair failed after about 100 miles. The seller/mechanic suspects the problem is a stripped head bolt thread on one of the forward cylinders, and he recommended I install an ARP stud bolt kit. Maybe it could be a slipped liner, but I think those rarely slip on the most forward cylinders? The copper-colored gasket partially covers the engine serial-number plate, making me wonder if the gasket was installed upside-down or backward?

The seller also told me the heads had been skimmed while they were off.

The spark plugs in all eight cylinders are pretty black, but are evenly blackened. Mostly carbon, I think.

The entire engine is about as grease-covered as it can possibly be. Presumably that's normal?

When I drained the oil, the first stuff to come out of the drain hole looked like liquid aluminum. I'm guessing it's suspended water, or microscopic aluminum particles that had settled to the bottom of the oil sump, or some sort of BS engine "stop leak" additive. In all, I drained 7 quarts of oil from the block. The oil was very dark, and stunk with gasoline fumes.

With a known "gasket" issue, and with no water pump attached, what diagnostics are worth doing, and in what order? Leakdown tests would hopefully establish decent compression for 7 of eight cylinders.

Given the mileage and the indicators I have above, what to do first?

Any advice, observations, ideas, would be welcome.

Many thanks!

Dave

It's quite possible that what's happening is that one of the cylinder liners has slipped. I've heard, and seen pictures, of a repair for this problem - drilling a hole in the block and inserting a bolt to pin the liner to prevent it from slipping.

Dave,

With aluminum particles in the oil, it most likely has a bad main, rod or cam bearings. If there was quite a bit then there is a very good chance that it has a spun rod bearing.
The wise thing to do would be to tear it down for a full inspection, as opposed to trying to get it running as is and risking further damage.

Bill

Hey Dave,

Bail!
Al that nice aluminiumie.. stuff in the oil was likely emulsified oil.
You are most likely looking at a cracked block. And the expense to get a machine shop to confirm that is more than the block is worth.
As well, having coolant in the oil on more than one occasion , has probably trashed the bearings and possibly the cam and lifters.
So I would pull it apart, examine it carefully, and learn from the experience.
Then go out and find a new block to put your 4.6 parts into. There are tons of 4.0 engines out there looking for your 4.6 innards.

Cheers
Fred

Many thanks Bill, Paul, and Fred,

All signs point to this engine being primarily a teaching tool and some questionable spare parts! I do have a glimmer of hope though.

I'll explore the stuff in the oil a bit further this eve. If it's metallic, from a spun bearing, it should be magnetic, yes?

If it's not metallic, and if I heat it up, the emulsified water should boil off, yes?

If it turns out to be an emulsion, and if there's no metallic particles or other signs of spun bearings, is it worth investigating the last head gasket job?

I attached an interesting (to me anyway) photo of what I've got now. Is it odd to have an asymmetric bit of gasket protruding from the union between block and head, between the middle cylinders on both sides? Maybe the last guy put the gasket on backward, or upside down, or on wrong cylinder bank? It seems pretty thin. Is it even the right kind of gasket for a late 4.6? Is it reasonable to think the last gasket "repair" was too sloppy to be effective?

If I have a coolant emulsion only, I 'm thinking I'll take heads off, look for signs of coolant/corrosion in bolt holes, look for signs of slipped liner, and if I don't see either, I could try a set of ARP studs, new head gaskets, and a new leak down test. Would that leak down test mean anything if I don't start it up and run it for a while first?

Any diagnostics I should do before I start the tear down?

Thanks again for all your help.

Dave

I would pull the oil pan, spark plugs and valve train off.
Build an adapter to let you pressurize the cylinders with air through the plug holes. Often your compression gauge has the correct fitting for this.
Pressurize each individual cylinder. But be careful as the engine will do a partial revolution each time you change cylinders.
You should be able to find the leaking cylinder easily enough this way.
I'l bet that you will find air bubbling out between one of the cylinder liners and the block.

Dave,

If it does have a spun bearing, most of the particles will usually be babbit bearing material and may not be magnetic. (Although a small amount could be if it was from the rod itself)
As Fred mentioned, I would pull the pan and plugs to do a leak down test. Then after your leak down test is completed, pull the main and rod bearing caps for inspection. This should tell you what you have to work with and whether or not if it's worth saving.
When pulling the caps be sure to mark their location!

Bill

I have read that sometimes the slipped liner issue does not show itself until the engine is a operating temperature. The cracked liner can be found without heat.

[robisonservice.blogspot.com]

An iron block solves the problem.

Jim

Hmm, a destroked Buick 300?

Hi Jim,

I'm not ready to drink the Buick 300 Kool-aid (yet!).

The diagnostic process here is something worth walking through. The local pick-a-part yard here in VA has a half-dozen Rover v8s, all for less than $200 if you can remove it yourself, $350 if you need help. There's real savings to be had, even if it takes three or four engines to get one that's still sound. Sale of T he parts off the dead ones can fund further efforts.

I'll post results of Bill's air pressure pressure tests soon, hopefully after the weekend.

I also saw this comment on the Pirate4x4 website:

"TBH the liner actually slipping in the block is quite rare. Also, some if the blocks are machined with a slight ridge at the bottom of the bore that the liner almost sits on. The much more common failure is a crack behind the top area of the liner into the coolant jacket which then leaves it open to pressurisation from gases that are forced between the liner and block casting due to the complete liner being within the fire ring. During the non compression / firing stoke the pressure is released back into the cylinder as coolant & steam. This generally gives all the symptoms of head gasket failure apart from one detail …………. a compression test will show up as OK, whilst a compression test on a faulty head gasket will show poor compression on one or more cylinders."

The mechanic I bought this engine from said he saw a compression leak in one of the most forward cylinders, before and after the gasket repair.

If the above quote is accurate and valid, and if my mechanic was lucid and competent when analyzing my engine, I'm guessing I either have a garden-variety stripped head bolt causing head gasket failure, or a relatively rare type of cylinder liner or block defect.

I'm curious what y'all think, am I on the right path?

Dave

I thought everyone might like to see what came out of the oil sump. It looks like Baileys Irish Cream.

For even more work, you can block off the coolant passages in the block, liquid soap the suspected areas and apply air pressure. Sounds bubbly. Good Luck, art.

I wasn't ready to "drink the Buick 300 Kool Aid" either when I did my first conversion Dave, "Too heavy" I said. "nobody's doing it" I said. "Don't need that big an engine." I said. I also said, "I can drag 215's down off Jack Sanders' hill all week long for $40 a pop."

Well, 30 years of messing with 215's have taught me a few things. (And yes, a 215 is not technically a Rover but it all still applies.)

Just trying to save you a little time and money. Ask Chris Gill what he thinks. Bear in mind he did go overboard, building a stroker motor 350 but I think he's OK with the outcome.

Jim

>Hmm, a destroked Buick 300?

Actually, I wouldn't. Stock bore +.030" and stock stroke would be the most economical and reliable build, gives great power, and is going to be docile to drive. maybe a warmer cam later on if desired. It wouldn't be your build Carl, but I know you've driven Mikey's car quite a bit. I'd be sorta surprised if you didn't like it.

The iron block would give better reliability with a high revving destroked motor. It is more rigid, has better threads, and no liner issues. But you would have to run very long rods, stock 300 rods are 5.96", already a fairly long rod, and you have around 1" to 1-3/16" that you can move the pin up in the piston, plus say if you used the 2.8" crank instead of the stock 3.4" one, that's another .300", meaning your maximum rod length could he as much as maybe 7.450". That's a lot. In a 2.8" stroke motor it gives a rod ratio of 2.66, extremely high. Acceleration forces on your pistons would be higher than with a shorter rod but side thrust would be minimal. Forged pistons would almost be mandatory. But that is at the extreme.

[users.erols.com]

If you used your 4.2L Rover crank with the 3" stroke, (Which I know you are in love with because of the Chevy 3" stroke engines) that means your maximum rod is 7.350 so you could use the 7" Scat rods for the FHF which use the SBB bearing shells (BOPR). The weight of that rod is 564.5 grams so it's very light. A matching forged piston would be about 450 grams. The piston pin would need to be moved up about 3/4" from stock so you would have to find a piston, one with a 3/4" wrist pin, or you could probably bush the piston bores. That would give a rod ratio of 2.33, still pretty high but maybe something to consider. The SBC 302 had a 1.9 rod ratio. It would suit your preference for mid to high rpm torque. F1 and motorcycle engines go over 2:1, how far over I couldn't say. 1.75:1 is generally considered ideal, as is a 1.250" piston pin height. (leaves room for the rings, helps minimize rocking, reduces piston weight) You aren't going to get both in a destroked 300 without a very long rod.

Using the 1.75 rod ratio and working backwards gives a 5.25" rod with the 3" crank and a pretty tall piston. The Buick 215 used a 5.66" rod and that is about as close as you are going to get, giving a 1.89 rod ratio which is really quite good. But that means the wrist pin of the piston has to be moved down half an inch. The piston/rod assembly will be heavier as a result, and again a forged piston will be needed.

If you ran the 300 rods at 5.960" you would have a 1.99 rod ratio. With that you would only have to increase the piston's compression height .200" from stock 300. This then, represents the most practical destroker build, using your crank and everything from the 300 except the pistons. Your piston acceleration would be high and the piston would be rather heavy for a high winding motor as are the rods, but for a Buick based build it has potential. Add a set of TA heads and you might have a pretty good engine.

With the 340 rods: 6.387", 2.13 rod ratio. (350 rods: 6.358", 2.12 rod ratio) You might have better luck finding a piston for one of these combinations.

So a destroked engine would be feasible if you are willing to go over 2:1 on the rod ratio but below that I don't really see the point.

Jim

Quote:

"Jim B.
It wouldn't be your build Carl, but I know you've driven Mikey's car quite a bit. I'd be sorta surprised if you didn't like it.

I do like, very much. What's not to like? I have driven Mikey most excellent ride many times over the years. It is well built, well sorted, nice & tight, more than enough torque, no surprises. Even a grandma could take it to the grocery store, if her right foot behaved.

Quote:

Dave
If the above quote is accurate and valid, and if my mechanic was lucid and competent when analyzing my engine, I'm guessing I either have a garden-variety stripped head bolt causing head gasket failure, or a relatively rare type of cylinder liner or block defect.
I'm curious what y'all think, am I on the right path?

IMO the problem two separate problems. Slipped liners & small cracks in the block behind the liners. I don't believe either are rare.

Slipped liners were a problem with earlier block. Lots of pictures out there.

The cracks behind the liner are a problem with later blocks. There are various theories about this being caused by the head bolt hole threading during manufacture or the wrong torque of the head bolt.

The knocking of the later blocks while blamed on slipped liners appears to be piston slap.

Did you read my link?

[robisonservice.blogspot.com]

[www.rangerovers.net]

"The Yamaha YZF R1 is a typical modern sports bike that revs to 12,000 rpm. Its engine has a stroke to rod length ratio of 2.12:1 which is suitable for high rpm use. This can be compared to a Nissan SR20DE engine which revs to 7700 RPM with a rod to stroke length ratio of 1.58:1"
[www.motoiq.com]

I also saw where a 2.2 to 2.8 rod ratio is not uncommon in F1, along with a supposed quote from Smokey saying, "..use the longest rod that will fit...", and other engine builders who think shorter is better for reasons of valvetrain stability and better intake runner geometry. Many seem to think it is an unimportant issue.

So, back to your regularly scheduled program of trying to find a rod and piston to match the deck height. Best of luck.

Jim

I always thought the issue with the short rods was the rod angularity. Of course, it is always more complicated. There are pros & cons for both short rods & long rods.

[www.stahlheaders.com]

[victorylibrary.com]

I have another theory on the cracking behind the liners. Wildcat Engineering ( actually from Des Hamill's Rover V8 book on Wildcat Engineering)had a excellent article on the later Rovers. Rover used .007 interference for the sleeves and when overheated cause the cracking below the headbolts. Most other engine sleeves use .003-.004 interference fit. At about 200 degrees F, iron and aluminum expansion is pretty close. When overheated aluminum can expand over twice as much as the iron liner causing tremendous stress. Wildcat have used straight sleeves up to 3.78 in the later Rover pink graded blocks. Why would the stock sleeve have a chamfer on top at the fire ring? I wonder if you turned the sleeves around so it would be flat on top?

[books.google.com]



Edited 2 time(s). Last edit at 05/26/2016 09:09PM by mgb260.