MG Sports Cars

many of y'all are quite familiar with my Buick 215 & its blowby issues.. Last night I broke down & did a compression test. Here's the results:

Dry/Wet

1. 170/177 2. 179/185
3. 182/188 4. 171/177
5. 160/165 6. 184/191
7. 173/177 8. 170/175

I was expecting much worse numbers. Spark plugs were quite clean, too. Engine seems much healthier than I thought, except for all the blowby.

Carl, How is your PVC valve/breather. Plugs look a little lean in picture.



Edited 1 time(s). Last edit at 03/28/2010 01:29PM by mgb260.

Yeah, they are a tad lean. #2 is the leanest.

I still have a bit of stumble just above idle. I thought it was because of being too rich with this Carter 500. Maybe it's a bit lean off idle.

Did away with the PVC system when it took 9 quarts of oil to get to the Wisconsin V8 Meet. Don't tell anyone, but I'm running the old fashioned, hotrodder system (breather cap in valve cover).

With the numbers above, I'm at a loss why I have so much blowby.

OK, I have an idea.Your breather cap should be opposite as far as possible from road draft tube which should be low enough under car with angle cut to scavenge properly. For example: breather right front/road draft left rear or vice versa. My brother's Camaro had blowby problems too. He put a piece of stainless kitchen scrub pad in line between the PCV and motor.



Edited 1 time(s). Last edit at 03/28/2010 02:08PM by mgb260.

I had a proper closed PCV system when this all started. I one of the lines from the valve cover to this catch can:

[www.roadraceengineering.com]

Put an Edelbrock valve cover breather on the other valve cover in an attempt to stop oil from coming out every gasket in the engine. No draft tube like on my dad's stock '63 B.

This sounds odd to me??

Your compression figures seem quite high / good for a 215.?

9 quarts of oil... To go how far???

9 quarts is 18 pints yes??

My last race engine was a 215. I set ring gaps to 55 thou for nitrous use as opposed to the normal 19-20 thou.

My latest engine is a 4.6 / 280ci engine with 60 thou ring gaps. It breathes real heavy. I have a 1/2" breather on each rocker cover and I have converted the filler cap into a full bore breather as well. I only just get a small amount of oil gathering around the mesh of the rocker cover breathers. These are simple K&N filters.

On my 4.6 I get dry compression figures around the 140 psi mark and my engine does not use much oil??

Do you actually have excess blow by, or do you just have leaky gaskets??

I run 200 to 300 hp of nitrous on my current motor and I do not get any significant oil deposits on the breathers?? The mesh filters on my breather filters are my indicators for excess blow by.

When my enigine Idles I get a good mist from all 3 breather filters. But I dont use much oil??

This is an interesting problem ???

Carl, had similar problem with my 231 Buick. It is a long shot in your case, but mine was the dip stick, yes wrong dip stick and I was over filling by 1/2 a quart. Now that is not much and do not aks why..............but my oil pan is for a 4.5 quarts with filter.

Another problem I had in my 400 ci chevy small block was the valve covers had no bafles. Easy fix, just bought a set of groumets that act as bafles. $2.50 ea.

Another problem I had in my big block chevy was to much oil on the top, had to place restrictors on the oil feed holes from the cam. Now, this is interesting, The return oil hole was plugged it had a brocken drill bit from the factory. This kept the oil on the valley and it was sucked by the PVC when open. It was like a blow by problem. Reason why I got the engine cheap.

I remember in WI your oil breather was to small.

Plugs are to light in color. With the carter/Edlebrock change the primary needle to the step needle and not the economy needle which has a taper, do this first. Buicks like lots of advance so a richer mixture helps. (it hs to do with cam timing/profile)

I wish I was closer to give a hand.

Seems odd to me, too.

Yep, 9 US quarts (18 US pints). to go 850-900 miles. With the PCV it was pushing oil out everywhere. Removed the PCV & added a valve cover breather to the atmosphere. Only used one quart on the way home. Blows more at high RPM, naturally.

This is a factory high compression (JN block) Buick 215 engine.

I'll not claim to be an authority but I've noticed a couple of things that could be important. First, I'm pretty sure you've run the engine with the valve covers off but I don't remember how much oil you were getting in the top end. That is an important question to answer, enough oil up there and you'll never separate enough of it out to prevent it going out the breather lines with predictable results.

Next, because your original MGB cast valve covers are British, they almost had to have been set up with one unrestricted line to each SU carb and an orifice somewhere as a fresh air inlet. Although that system might have worked OK you'd have to duplicate it exactly for similar results and that's not what you had on the car. Plus it'd require recalibration of your carb if you did. Any restriction in the lines such as a PCV valve or a "T" to plumb them into the carb's single PCV connection would introduce a restriction significant enough to cause blowby to escape. Which means, you'd have to plumb each line unrestricted directly to intake vacuum and then put a fresh air inlet orifice on the oil filler cap. And then tune the carb to run that system. In doing so it is extremely important to place a flame trap in each line to prevent a crankcase explosion.

So consider the differences. In this system you meter in a reasonably steady flow of fresh air (depending on vacuum level) and you basically have to enrich the idle circuit to compensate, with also some enrichment in the midrange. Your idle speed settings will most likely have to be reduced as well. WOT is unaffected because with near zero vacuum and significant blowby under power no air will be drawn in. The blowby will bypass the carb so metering is unaffected. In the American system with the PCV valve matters are not quite so simple, but your carb is set up to compensate already, so in terms of the simple solution this is it. At part throttle the PCV is the restriction and meters fresh air and blowby (not much usually) into the intake below the carb, but at idle the vacuum probably shuts off the PCV valve. (This can vary considerably from one valve to the next). At WOT the PCV valve should be open but it does not have the capacity to flow all of the blowby generated to the engine and the bulk of it backflows up the fresh air vent line into the air cleaner housing and down the throat of the carb. This causes additional enrichment because the carb is metering burned gasses and it doesn't know the difference between them and fresh air. Remove the fresh air vent line and you'll run lean under power. Speaking of which, it looks like your #8 plug has a spot on it so you might want to get that squared away.

You can go with either system, both can be made to work well. But a mix of the two will not, it has to be one or the other. We discussed the use of the fuel pump block-off plate as a location for a large diameter vent line and this should work well for either system (correctly plumbed) as there isn't a great deal of splash in that area and an upward path from there will do much to separate out what there is. Some sort of flame trap is needed on this line too. GM commonly used a filter element inside the air cleaner housing. The Brits commonly used a metal mesh of some sort. A stainless pot scrubber in a container of some sort works well, this is similar to the large fitting you see on Rover valve covers. On the MGB-V8 there are devices in the lines that look like a weird short metal fuel filter housing. If the flame trap is also used to trap oil vapor (common) it must have a significantly larger diameter than the line in order to allow the vapors to slow down so the oil can be collected on the mesh and drip back down into the engine.

Now this large line from the crankcase when used on American cars was typically a 5/8" or sometimes 3/4" diameter and that is a pretty good guideline. The Brits used a similar sized line when a single line was used but instead of plumbing it into the air cleaner housing ran it to the intake manifold. As noted, it will work either way but the entire system needs to be consistent. I would say that using an American PCV carb with the British system you would need to enrich your idle and top end, adjust the idle speed down, and the midrange would either be unaffected or rich. Since your valve cover fittings are for a 3/8" line IIRC both in combination running unrestricted directly to the manifold will only flow half of what a 3/4" line will, and your hose barbs were pretty restrictive too as I recall. You can make them work, but only with a perfect configuration, probably meaning original fittings and flame traps, and connected individually to the intake plenum rather than the carb.

You have several options but you have to make a decision which way to go with it and we really didn't get into that on the phone. Feel free to call back and we can get into more of the details if you like.

JB



Edited 1 time(s). Last edit at 03/28/2010 08:37PM by BlownMGB-V8.

Then there's that head gasket question haunting me. These engine were known to leak combustion into the intake valley via the head gasket because of the three row head bolt design. No way I know of to check that 'cept pull the head.

A buddy of mine recently had a stroker motor built that had a similar issue. The builder insisted it was normal for a Rover. After much back and forth between my friend and the builder, the car was taken to another engine builder for diagnosis. First a compression test was done that looked similar to yours. The leak down test showed several cylinders that had 10 to 15% leak down. A boroscope inserted into the cylinders thru the spark plug holes showed severe washdown of the cylinder walls, bad vertical scoring, and very little cross hatching left. Once the engine was torn down, it was determined that the block, and pistons were toast. All of this damage was done in less than 1000 miles. If the rings don't seat in the first start up, they never will.

The head gasket problems I've had were always either leakage between the cylinders or leakage into the water jacket. I never had one leak into the crankcase. Not that that helps much....

JB

Call Mark at D&D time for some expert advice. He knows this engines very well !!!

Quote:

Then there's that head gasket question haunting me. These engine were known to leak combustion into the intake valley via the head gasket because of the three row head bolt design. No way I know of to check that 'cept pull the head.

Last year I swapped my original Buick 215 (five bolt per cylinder) heads for Rover 4.0 (4 bolt per cylinder) heads to get an increase in compression ratio (due to the smaller combustion cavity) and also slightly bigger valves/ports.

I was surprised to find that one of the two old head gaskets showed black staining from one or two of the bores up toward the valley pan. (It's a fuzzy memory now, but I think it might have been cylinders one, three, or both one and three. It was only on one side of the composite head gasket.) Anyhow, I wasn't aware of a compression loss before I upgraded heads. My theory is that the leakage only occurred under very high load, and it probably wasn't going on for very long.

Oil loss did go down with the new heads, but some of that might be due to the valve guides being in better condition. I have a breather-type oil cap on driver side and a PCV valve on passenger side. The breather still seems to drip a little oil from time to time. It's a little annoying, but not enough oil to really piss me off.