Z1 Oil breather advice

Hello to all,

I currently have a 1974 Z1 in my 1974 Legrand D Sports Racer (SCCA vintage car). I recently went through a top end rebuild that included pistons and rings as well as honing the barrels. After an open test session at Thunderhill raceway in Northern California last Sunday, I have a problem; the motor is dumping large amounts of oil from the breather. This only manifested itself after driving on-track. No problem in the shop running the engine with the car stationary.

One of my friends (and old Kawi builder) said that it could be a couple of things.

1. Rings need to seat: It could be that I am getting blow-by into the crankcase thus pressuring and blowing the oil out. Cure? Run the engine until they seat or if they don't seat, re-do the pistons/rings.

2. Reduce the velocity from the breather: I have a 90 degree fitting into a tube that goes from the breather outlet into burp bottle at the back of the car. He suggested that I increase the diameter of the tube (and fitting) to reduce the velocity.

3. Overfill of oil: I am running a cooler at the front of the car and a modified pan that has a cylindrical cup attached to the bottom with a tube that scavenges from the pump (kind of a cheater sump). It is entirely possible that I did overfill, however once I had lost probably a quart to a qt and a half, my idiot oil pressure light started to flicker. After adding a quart, it went dark so I feel I am pretty close to the right level.


I would be interested in hearing anyone's thoughts/advice regarding this.

Have you experienced this after rebuild?
Thoughts on breather tube diameter increase reducing velocity?

I apologize for the rather lengthy post but hope some fellow KZ folks might have some thoughs/advice.

Quote "1. Rings need to seat: It could be that I am getting blow-by into the crankcase thus pressuring and blowing the oil out. Cure? Run the engine until they seat or if they don't seat, re-do the pistons/rings."

There are many theories with regard to seating rings. I would say that if as much oil escaped as you describe, yours didn't seat. I am also fairly sure the walls are glazed. Did you do the rebuild? If so, did you measure piston to cylinder bore clearance? Just dropping a new set of rings on worn pistons in worn bores won't solve sealing problems if the clearance is out of spec. I rebuild a few engines every year and if the piston to bore clearance is within spec, have never had one blow much oil. Also, my take on "break-in" is that you are not really breaking-in a 30 some year old engine. You are just trying to seat the rings. I firmly believe that ring seating doesn't need to be slow or dainty... mainly avoid a single rpm and ride it like you stole it.



Quote: "2. Reduce the velocity from the breather: I have a 90 degree fitting into a tube that goes from the breather outlet into burp bottle at the back of the car. He suggested that I increase the diameter of the tube (and fitting) to reduce the velocity."

That isn't going to work... only ensure that the oil blows out FARTHER... make sure the tube into your catch bottle isn't bottoming in oil as this will seal the crankcase and cause engine damage. The oil in the catch bottle should never get up to the hose outlet in the bottle itself. Make sure the routing of the hose doesn't create a catch for the oil; that is:
--- ----
|_______|

This type arrangement allows the oil to sit in a low section of the breather hose and it will fill the hose and obstruct breathing... engine damage will result.

QUOTE: "3. Overfill of oil: I am running a cooler at the front of the car and a modified pan that has a cylindrical cup attached to the bottom with a tube that scavenges from the pump (kind of a cheater sump). It is entirely possible that I did overfill, however once I had lost probably a quart to a qt and a half, my idiot oil pressure light started to flicker. After adding a quart, it went dark so I feel I am pretty close to the right level."

If you overfill, its gotta go somewhere. Not sure on volume that will stay in the cooler but you DO have a sight glass on the right side of the engine. If you suspect over-fill, drain and refill to the bottom line leaving the filter in place. Top off after the engine warms.

A Hearty Welcome to the site, cplescia! We're glad you're here.


Excellent advice already from wg.


Would consider a leak-down test to determine blow-by (listen at breather vent for escaping air).

Dumping large amounts of oil from the breather after driving on-track, but not in the shop. Forgive my ignorance, but is this rough terrain racing? Breather opens directly into top of crankcase -- is oil splashing to top of crankcase.

Over-heated oil may worsen escape from crankcase via breather vent -- how is cooling air-flow over engine fins provided? As known, oil cooler alone would not provide sufficient engine cooling.

Would maintain same ID in vent hose as ID in vent nipple, without any downsizing, crimping or restriction anywhere in vent hose. Be extra careful at 90 degree bend from attachment at vent nipple. And would not use any filter at end of vent hose or anywhere else (as filter is too easily saturated and clogged). Would assure breather is clean and unclogged.

Not fully understanding the modified pan with cylindrical cup attached to the bottom with a tube that scavenges from the pump (kind of a cheater sump) -- unless this is functioning simply as a deeper pan to allow additonal oil capacity. Is a windage gate in place (to aid pick-up by oil pump during hard acceleration)? As known, windage gate can help avoid flickering oil pressure light where crankcase oil volume is correct.

Just my thoughts (with no experience whatever using KZ engine in a race car). And if any conflicting advice detected, go with wg :laugh: .

Good Luck!

Post edited by: Patton, at: 2007/12/27 14:50

First, thank guys for responding so quick!

Wiredgeorge- I appreciate the answers for all points. Specific answer regarding point 1:

Yes, I did the rebuild myself (probably first error but we gotta start somewhere). The barrels were honed so not sure about if they were still glazed. I assumed not. I did my best to measure everything before reassembly. While I agree that your hypothesis is valid, I was wondering if your experience with this manifested itself during idle and when the engine was stationary? This only happened when out on the track. Additionally, it seemed that it wasn't as bad when I wasn't really driving the car hard (75% vs 95%).

I haven't done a compression check yet but was wondering if the rings weren't seating, whether I would have low compression? I can check it and may indicate one way or the other.

The motor ran the best it ever has. I had the nest low end torque that I have experienced so I was very pleased with the performance, just had the oil blow out issue.

Patton- to answer your questions:
Not rough terrain. This is paved road racing. The engine sits in the back but I have a fiberglass snorkel that flows cool air over the head and over the rest of the engine.

I have both Head Temp and Oil Temp guages. Head temp was about 400 (redline is 450 degrees) and oil temp was about 235-240. Ambient was around 60 degrees.

We've run the engine in this configuration for about 6 years. I have included a picture of the cup I mentioned.

Thanks again for all the thoughts!

Post edited by: cplescia, at: 2007/12/27 16:06

something you didnt mention, what fuel are you running?
and what was the result of the compression test? what do the plugs look like?

What size pistons? Did you gap the rings?

Jay

Again, thanks for all the advice so far.

I did a compression check and here is what it read:

#1 = 149 (some carbon dust)

#2 = 140 (clean)

#3 = 156 (clean)

#4 = 155 (clean)

I guess the question would be that if I had low compression, this could create a condition where by blow-by was moving into the crankcase thus pressurizing and creating an oil evacuation issue?

To answer a couple of questions;

BSKZ660- Compression test results above. I am running 110 octane race gas (76).

APE Jay- I did gap the rings. Pistons were stock 900's I got from eBay. I did mic everything prior to reassmbly and all appeared within tolerance.

If my compression theory is true (meaning good compression=limited blow-by), then I will start to look at oil overfill as the cause.

Those compresion #'s arent bad.
I had this problem with my 1135cc motor after it sat for 23 years.compresion was 140 and it only blew oil at high rpms.after new rings and a hone (.0015" pist to wall), i had no more blow by.psi is now 150psi.
i'm not convinced you have too much blow by , yet though.

I wonder if u have a vent at the catch can ? without a vent somewhere u do not relieve the crankcase preasure.
i like the idea of a larger tube myself.lots of guys add aditional vent lines,this would be the same as a larger line.u can add 1 to the kick start hole or cam cover.

Thanks for the ideas Mark. My catch can is vented (has two holes at the top.

I had the same idea about an additional vent added to the cam cover. If and when I figure it out, I will update (for someone elses edification).

u can run a line from the oil cap too, basicaly anywhere there is a hole. just make shure it is baffled so u dont get more oil. can u tell me about oil temps . i am adding a 1327cc kit, and an oil gauge at the oil presure gauge area. how hot is too hot?