Barffing up blowby on my Matchin 75 L20b

[datsunaholic]

When he took off for a test run it smoked on shifts. But that's hardly telling... there was a good pint or 2 of oil sloshing around in the air cleaner (I'm not kidding, you could have poured the oil out of it) and while he mopped up most of it, there was a bunch still left in the snorkel and all over the carb air horn.

 

I've seen normal cam oil slinging. I've run engines with the valve cover off to check cam oiling. This was excessive, and it came with a bunch of air pressure.

 

Hainz: his engine is original, squareport U67 head with heatstove (mated) manifolds and no coolant lines to the manifolds. It's had the EGR manifold removed and the ports plugged with setscrews, and a fairly hokey collection of pipe elbows to connect the PCV to the intake where the EGR manifold used to be. Stock carb, stock air cleaner, but all the emissions equipment was pulled so there are a bunch of non-connected vacuum lines. Oil was coming out anywhere there was supposed to be a vacuum line on the air cleaner (since nothing was plugged, just left open)

[PtheDude]

Thanks Datsunholic. I'm thankful you were able to look at it and know exactly what was up. Square port head. The rebuilders have asked about that.

[datzenmike]

Was the EGR tube on the exhaust manifold plugged off? Any chance it was connected to the PCV tube going back to the baffled side of the block? This would allow exhaust access to the inside of the block. Hainz: I'm reaching too lol

[///FiveOneOh]

Was the EGR tube on the exhaust manifold plugged off? Any chance it was connected to the PCV tube going back to the baffled side of the block? This would allow exhaust access to the inside of the block. Hainz: I'm reaching too lol

 

hey I've seen a coolant line off the intake mani hooked up to the block beather before....:confused:

[ppeters914]

L20 round or square exhaust? I dont know the year break down on these Doug would know

According to the Wikipedia, it was 1977.

 

Is there really any difference between the U67 (square) and the later W58 aka smog head (round)?

[datsunaholic]

Is there a difference? Yes, the exhaust ports are square vs round!

 

Ok, ok. Intake port size was the same as were valve sizes. Exhaust ports had steel liners in the round ones. U67 heads don't have coolant ports to the intake manifold (they can be added with a drill)- the reason is the U67 head was exclusively used with the stovepipe manifold. That had a blend door and a heat plate to prevent icing, whereas the 74 and earlier and 78-later L-series used coolant to heat the intake.

 

Other... there are rare cast-iron U67 heads, some of those were closed-chamber. That's the only Nissan cast-iron L-series head I've ever seen (it was used for factory Propane setups)

[ppeters914]

Is there a difference? Yes, the exhaust ports are square vs round!

I just KNEW you were gonna say that. :mad: Thanks for rest though. :D

[tnip]

would the cast iron propane head be like the ones in a forklift? and if you used that cast iron head couldn't you shove a ton of boost into the motor if you used a lil beefier internals? and then run something insane like 2 bars of boost and make a good lil bit of hp. :) haha

[datsunaholic]

The ones I knew of were in trucks... Boeing bought a ton of 620s with propane setups to use as shop trucks for driving around/in the assembly plants. I have the propane setup from one, but not the head (the guy had it, but wanted way too much for the head).

[datzenmike]

I don't think strength is the issue even with that much boost. The Al head would conduct the heat away from the cylinder better than the iron one I would think, that and it's lighter. Good insane idea though!!!.

[lynchfourtwenty]

ok so my 1977 620 had a u67 head.. i bought a a87 closed chamber head.. i used the same intake mani that was on the u67.. i dont remember seeing water jackets on either head.. an i compared them side by side to make sure it was the same shit.. altho it was years ago and i didnt know about the water jacket thing then so i might have over looked that.. But i have no coolant leaks .. so either my a87 head doesnt have the water jackets.. or my u67 intake mani has some.. or something.. cause i didnt block them off so you think they'd leak or something if the mani didnt have the holes to match .. any thoughts?

[tnip]

I don't think strength is the issue even with that much boost. The Al head would conduct the heat away from the cylinder better than the iron one I would think, that and it's lighter. Good insane idea though!!!.

 

well i was thinking of the alfa 159m when i posted that. made in 1951 it was a formula one car that had a 1.5 litre straight 8 with twin superchargers, single carb. it ran a gas ethanol mix and made like 450 hp at like 9500 rpm. only got a couple miles per gallon because they ran it super rich just to keep it cool, as it was pushing like 35 psi. that car always stuck in my mind cause while ferrari and other "big" companies were using the other formula one optional displacement of 4500cc, alfa just kept pushing the limits of their 1500cc engine. in the end the reason it failed was because of the fuel comsumption. it's a very interesting lil car. that engine was designed in 1937 by some nazi funded engineers and started life as a 1.5 liter straight 8 with a single blower that made like 200 hp.

 

edit: some of my numbers are a tiny bit off. here's the corrected numbers:http://www.ddavid.com/formula1/alfa158.htm

[datzenmike]

Good read! Some of the read old engines (Auto Union) made their power by increasing cu in to like 800. Tires would spin at all speeds.

[PtheDude]

My blowby got a little off track into alpha land... back to point:

 

did compression on the 75 tonight

 

1 -125

2- 100 :(

3- 100 :((

4 -110

 

I can hold my finger over the valve cover breather tube for 30 seconds and it builds up enough pressure to pop and phiiissssssssss pressure out.

 

Pretty sure I hear #3 valves knocking around.

 

Its got oil, dipstick tube is secure, changed the oil filter ( oil drained out, oil filter not obstructed inside)

 

What's next? Pop cover and check valves? I have the how to keep your datsun alive book, it goes over a few procedures, for engine examination.

 

Is it pretty much toast?

[lynchfourtwenty]

might as well check the valves before you assume the worse.. get a $5 valve cover gasket and adjust those babys if they need it.. if they're in spec.. then idk.. its just a suggestion.. hope it helps!

[banzai510(hainz)]

http://www.guba.com/general/search?query=datsun&set=5

I think it give a very basic instruction at the last part of this vid

 

I set mine to .006in and .008ex cold warm

 

But you can set yours to the book

 

Loosen the 17mm jam nut then move the 14mm post up/down with the cam lobe UP from anywhere in the 10 -2 o clock position. stick feeler gauge between rosker and cam lobe then adjust the 14mm then once you have it lock it down with the 17mm jam nut.

 

I dont think this is your proplem unless a seat maybe loose or somethin but it the seat was loose I would think you have lower compression #s

[PtheDude]

So its toast. damn it!

[datzenmike]

My blowby got a little off track into alpha land... back to point:

 

did compression on the 75 tonight

 

1 -125

2- 100 :(

3- 100 :((

4 -110

 

I can hold my finger over the valve cover breather tube for 30 seconds and it builds up enough pressure to pop and phiiissssssssss pressure out.

 

Pretty sure I hear #3 valves knocking around.

 

Its got oil, dipstick tube is secure, changed the oil filter ( oil drained out, oil filter not obstructed inside)

 

What's next? Pop cover and check valves? I have the how to keep your datsun alive book, it goes over a few procedures, for engine examination.

 

Is it pretty much toast?

 

Cant see, or having a hard time understanding why the excess pressure doesn't go out the breather on the valve cover?? How can it build up inside the block with that opening there??? Is the hose partially plugged?? The PCV valve may be replaced but is the hose to the block plugged??

 

Hainz, could an exhaust valve GUIDE be broken? This would allow exhaust pressure up into the valve cover area. ??

[]2eDeYe]

With my last motor I had the same issues. I had a broken ring or 3 :P

[banzai510(hainz)]

I mention the seat issue may casue the air is going into the head/crankcase area.

 

I had alot of blowby on one motor. I had a open crankcase vent since I had sidedrafts. At idle it will blow out smoke. But when you increase RPM it will suck IN cause of neg pressure. Was also told this by someone else.

 

 

The valve cover should blow out air at idle for sure anyways. I dont know at higher speeds but what I noticesd on my side crank case vent that it stoped smoking out the side when I increased speed. Proplem was all the ring wernt gapped correctly and wore in the same spot on all cylinders where the gap clocking was.