Crankcase blowby - warm versus cold

Crankcase blowby - warm versus cold

Eric Hamilton (Durham NC)
Eric Hamilton (Durham NC)

May 26th, 2008, 3:29 am #1

This afternoon I was checking out the newest member of the family - '74, 1300, green, all stock.

Compression was 135, 155, 155, and the fourth cylinder I couldn't check (that's my previous post ). Not great, seeing as how 155 is the -lowest- reading on the other car, but more indicative of wear than imminent disaster. There's a lot of slime in the air cleaner housing, so I wasn't surprised to find low compression readings: the slime is stuff coming in through the crankcase vent hose, which means lots of blowby, which means ring wear.

But I was surprised when I replaced the plugs and started it up and there was nothing coming out of the crankcase vent hose... Put my hand over the end of the hose and there was no pressure, no air flow at all. However the engine was cold, and as it warmed up, the vent hose started flowing fumes, and by the time the engine was warm, the vent hose was visibly smoking and stinkier than the exhaust itself.

So now I'm curious: Why would the rings, or anything else for that matter, seal better when the engine is cold? Just the viscosity of cold oil on the cylinder walls?
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Joined: December 21st, 2004, 3:04 am

May 26th, 2008, 6:35 am #2


With more than ONE X now... you can insert the helicoil and not change plugs for another two or three years...  No worries...

As for the blowby issue... Try some ATF down the carb... abotu 1/3 quart at 3000 rpm over 10 minutes.  Lots of smoke... but can help seat the rings.  Then retest compression and chck blowby.

BTW, You don't have an EGR on that thing do ya?  Smog pump?


My best,



Tony
Black Tooth and me... since 1983!
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Eric Hamilton (Durham, NC)
Eric Hamilton (Durham, NC)

May 26th, 2008, 3:14 pm #3

OF COURSE I have a smog pump; they came with all '74s. But I doubt mine is doing any harm; I maintain it very carefully: I fully rebuilt its cardboard box, then carefully cleaned and dusted the shelf before I reinstalled it in the back of the closet. I take it out of the closet every year to verify that it still functions properly; it should be able to weigh down three standard sheets of typing paper in a five-knot breeze.

No EGR. That came later. (Did any of the 1300s have it? I owned a '78 back in '78, that was the last year of the 1300, and I don't remember EGR on it).

I've been waiting for an excuse to try that ATF trick...
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Joined: December 21st, 2004, 3:04 am

May 26th, 2008, 4:21 pm #4


I mentioned the EGR as it should OPEN once the engine came up to operating temp and possibly be the cause or a contributor to the blow-by.&nbsp; Just a shot in the dark.

Lets just assume that the oil and engine have heated up and things have expanded... and that is the cause of the blowby...

1.&nbsp; Do install a new helicoil and then carefully take compression.

2.&nbsp; Do the ATF trick...

3.&nbsp; Take the compression again after the cops leave...

4.&nbsp; Note if there is any difference in performance and/or blowby.

5.&nbsp; Post the before and after results here with photos...


My best,



Tony
Black Tooth and me... since 1983!
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<font face_"Times Bew Roman" size=1>Disclaimer: This message does not necessarily reflect the views of the sender, or, for that matter, any other carbon-based life form; Any resemblance to actual persons, living or dead, is unintentional and coincidental; All models are 18 years of age or older; Dry clean only, do not use bleach, Tumble dry and remove immediately; Do not bend, fold, staple or mutilate; Anchovies, cheese or jalapenos may be added to orders upon request for an additional charge; Professional driver on a closed course, do not attempt to duplicate; Your actual mileage may vary; No substitutions are allowed; Available for a limited time only while supplies last; Offers are void where prohibited by law; Humor is provided "as is" without any warranties expressed or implied; The user assumes full liabilities and originator is not liable for damages due to use or misuse; We are an equal opportunity employer, with no regard to race, religion, sex, or sexual preference; No shoes, no shirt, no service; Read at your own risk; This post may contain material some may find to be objectionable; Parental advisory: Explicit lyrics; keep away from pets and small children; limit one-per-family please; No money down; No purchase necessary; Ask us about our guns-for-dope trade-in plan; You need not be present to win; Some assembly required; Batteries not included; Action figures sold separately; Contents were packed full at the factory, but may have settled during shipping; Peanuts and peanut products are produced in this establishment and also consumed by the author; Sanitized and sealed for your protection; Do not use if safety seal is broken; Do not use while operating a motor vehicle or heavy equipment; Safety goggles may be required during use; Use gloves when handling; Call before you dig; Use only with proper ventilation; For external use only, if a swelling, redness, rash, or irritation develops, discontinue use; Do not place near a flammable or magnetic source; Keep away from open flames; Avoid inhaling fumes or contact with mucous membranes; Contents under pressure, may explode if incinerated; Smoking may be hazardous to your health; No smoking allowed, except in designated areas; The best safeguard, second only to abstinence, is the use of a good laugh; Text is made from 100% recycled electrons and magnetic particles; No animals were harmed while writing this post; No salt, MSG, preservatives, artificial color or flavor added; If ingested, do not induce vomiting, If symptoms persist, consult a comedian; Ribbed for your pleasure, slippery when wet; Must be 18 to enter; No one under 21 allowed; We check IDs to age 40; Seniors Welcome; Ask for our Senior Menu; Present discount coupons to cashier before totaling; An 18% gratuity will be added to the total for parties of 8 or more; We reserve the right to refuse service to anyone. Return all carts to the store; No dogs allowed, except for the visually impaired; Penalties for early withdrawal, one size fits all; Offer is valid only at participating sites; Prices slightly higher west of the Rockies; Allow four to six weeks for delivery; If defects are found, do not attempt a repair, return to an authorized service center; Please remain seated until the vehicle has come to a complete stop; Objects in the mirror may be closer than they appear; Fasten seat belts; In the unlikely event of a loss of cabin pressure, oxygen masks will fall from above, cover your face first, then assist those around you. Your seat cushion may be used as a floatation device. This disclaimer is invalid in the event of hurricanes, floods, earthquakes, sonic booms, vibration, electromagnetic radiation from nuclear blasts or any other act of war, unauthorized repair, improper installation, misuse, typos, misspelled words, missing or altered signatures, and incidents owing to computer or disk failure, accidental file deletions, and Acts of God. Other restrictions may, or may not apply.</font>
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