Low compression band-aids?

[jturner]

28 minutes ago, TobyB said:

...fix your carburetor.

 

JTurner, that means you, too- those plugs are rich.  Probably burning oil, too, but the car's running too rich,

for starters.

 

And put an oil pressure gauge on.

 

Reason being, if you have 7 psi at idle, 30 at speed, you're much closer to a rebuild than with

25 at idle, 65 at speed, hot.

 

t

now we're cooking with gas!

 

Yes, the carb is absolutely knackered... 32/36 with the idle speed screw completely loose and it still idles. I assume the mixture is bonkers rich to keep it idling.

 

Problem is I'm ready to start a sidedraft conversion so I have no enthusiasm for that carb. I open the chapter on DGAVs in the braden book and my eyes just glaze over. I rebuilt it to stop a leak, popped it back on.

 

I only checked the compression to make sure I don't put sidedrafts on an untunable engine.

 

I'll do an oil pressure gauge... ignore Toby at your peril they say. That's why I installed a wideband...

 

 

 

 

[jturner]

24 minutes ago, percy said:

 

The plugs clearly indicate a rich mixture and what appears to be oil residue.  Changing: carb settings (leaner), plug heat range (warmer) and ignition timing (increase) are all things to consider as "low compression band-aids".

 

You mentioned the smell of burning oil.  Previously mentioned small oil leaks could account for this, but so could poorly ducted crankcase blowby.  The valve cover vent was typically ducted into the airfilter housing.  If, as you suspect, the engine is producing excessive blowby and/or the crankcase is venting in or near the engine bay, this could account for cabin fumes.  Obviously, the impact of blowby can be mitigated by venting as far away from the cabin as possible (lengthy downdraft tube), or via an engine rebuild.

 

Good advice for dealing with it, thanks...

 

Yes, crankcase venting was a mess when I pulled the carb off. Oil all over the place in there. I rebuild/cleaned the carb, and now I'm venting to a catch can, then to the road.

 

 

[chargin]

Drive it awhile and then retest, it could be carbon build up as well 

[Jimmy]

2 minutes ago, chargin said:

Drive it awhile and then retest, it could be carbon build up as well 

 

This, if it's that rich the rings are likely fouled.

[Mike Self]

13 hours ago, mlytle said:

just because compression is low, doesn't mean rings are bad.  could be intake or exhaust valves not sealing or adjusted too tight. 

+1

A quick 'n dirty way to determine what's leaking compression.  From a standing stop after idling for 20-30 sec, accelerate briskly in first and second up to about 35-40 mph, and watch your rear view mirror.  If you have a nice puff of smoke as you accelerate, that's rings.  Once you hit 35- 40 or so in second, quickly lift your foot off the gas and coast.  If you now get a smokescreen, that's valve stem seals. 

 

If you get both, your engine's getting tired!  But as my late and greatly missed father in law used to say, "Mike, oil's cheaper than engines."

 

My '69 used very little oil and smoked very little 'till I had to do some head work at 157k.  While the head was off I had the valves ground and fitted new guides and seals.  Then the rings were the weak point, and it started to smoke.  A little.  It's still smoking, a little, at 226k.  

 

mike

[fastricky]

27 minutes ago, mike said:

+1

A quick 'n dirty way to determine what's leaking compression.  From a standing stop after idling for 20-30 sec, accelerate briskly in first and second up to about 35-40 mph, and watch your rear view mirror.  If you have a nice puff of smoke as you accelerate, that's rings.  Once you hit 35- 40 or so in second, quickly lift your foot off the gas and coast.  If you now get a smokescreen, that's valve stem seals. 

 

If you get both, your engine's getting tired!  But as my late and greatly missed father in law used to say, "Mike, oil's cheaper than engines."

 

My '69 used very little oil and smoked very little 'till I had to do some head work at 157k.  While the head was off I had the valves ground and fitted new guides and seals.  Then the rings were the weak point, and it started to smoke.  A little.  It's still smoking, a little, at 226k.  

 

mike

 Great post and offered a laugh. ? (I like the dad-in-law comment)

Edited March 18, 2019 by fastricky

[KFunk]

I believe I drove cross-country with much less compression, and then autocrossed and daily drove it several years with unfiltered velocity stacks on sidedraft carbs.  Still ran great, just a bit of smoke on acceleration.  I tried to kill the damn thing, but I couldn't.  The thing about just a little slipping past the rings, is that it just gets slightly worse over time.  No boom of all things breaking loose, just tiny bits of war over tens of thousands of miles.

I did end up rebuilding it, but not because I had to.  I just had some time and money and wanted to try higher compression pistons and a cam.  It's an improvement, sure, but the old engine was damn fun too.

[irdave]

My tii motor has a little over 240k miles on it.  Still fun to drive.  Has some oil leaks, but it pulls nicely, even up here at 5k feet of elevation.  I don't know that 120 is a lot, assuming the engine was taken care of...

 

And oil smell can be cured with new trunk and hood gaskets...  Or by installing gaskets if they're missing.

[jimk]

Eventually it will need some rings.

[airborne85]

Cool topic.

 

For the longest time I've had a huge plume of smoke coming from the rear of my car on deceleration, especially on a daily spirited drive...Being in the SF Bay Area it almost feels like a criminal act just as soon as the smoke comes out....... Well, last month I tried an oil additive.....Hyper lube Zinc replacement ZDDP...I put this in after work. I work night time in Oakland.  I traveled to Richmond.  On the way to Richmond there's a nice stretch of roadway that's free of traffic, for the most part.  Of course I accelerated to a fun speed, then I caught up to traffic. However, when I decelerated absolutely no smoke (I was tired from the watch).  I tried the same thing over and over again, same results, no smoke..........View the above how you'd like.

 

ira

[TobyB]

Then throw the sidedrafts on there and start learning about them.

That much soot will eventually cause trouble of the JimK kind.

I have a piston that looks remarkably similar to that....

 

It'd be good to dial in new carbs on a non- new motor anyway-

if you have gross troubles, an old motor will tolerate them far better

than an unbroken- in one.

 

But the 32/36 works well into it's sunset years- there are several things that 

need attention, but they last almost forever, at slightly diminished precision.

 

t

[jturner]

33 minutes ago, TobyB said:

Then throw the sidedrafts on there and start learning about them.

That much soot will eventually cause trouble of the JimK kind.

I have a piston that looks remarkably similar to that....

 

It'd be good to dial in new carbs on a non- new motor anyway-

if you have gross troubles, an old motor will tolerate them far better

than an unbroken- in one.

 

But the 32/36 works well into it's sunset years- there are several things that 

need attention, but they last almost forever, at slightly diminished precision.

 

t

 

 

Good deal. Puts things in better perspective anyways.

 

Get it patched up and running with the sidedrafts and 123, then maybe a reworked head with 292, and maybe by then I'll be ready for the bottom end.

[Dudeland]

An interesting read from Hot Rod

 

https://www.hotrod.com/articles/0311em-power-squeeze/

 

15 COMPRESSION BOOSTING MOVES

 

1. Feed cold air to the induction
2. Keep water as cool as possible (170 F or less)
3. Keep the air cool in the intake ports 
4. Put a heat-reflective shine on the outside of the intake manifold 
5. Minimize heat transfer through the common exhaust/intake port wall 
6. Keep fuel temperatures down (cool can)
7. Run with plugs a little colder than the minimum required
8. Use an ignition system that is gross overkill
9. Utilize as large a spark plug gap as possible
10. Use no more ignition advance than is necessary
11. Maximize quench action
12. Minimize head chamber volume
13. Use flat-top pistons if possible
14. Minimize under-hood exhaust heat–use coated headers
15. Do not ram in but vent out hot air through hood vents

 

 

[Simeon]

 

6 hours ago, Dudeland said:

An interesting read from Hot Rod

 

https://www.hotrod.com/articles/0311em-power-squeeze/

 

15 COMPRESSION BOOSTING MOVES

 

1. Feed cold air to the induction
2. Keep water as cool as possible (170 F or less)
3. Keep the air cool in the intake ports 
4. Put a heat-reflective shine on the outside of the intake manifold 
5. Minimize heat transfer through the common exhaust/intake port wall 
6. Keep fuel temperatures down (cool can)
7. Run with plugs a little colder than the minimum required
8. Use an ignition system that is gross overkill
9. Utilize as large a spark plug gap as possible
10. Use no more ignition advance than is necessary
11. Maximize quench action
12. Minimize head chamber volume
13. Use flat-top pistons if possible
14. Minimize under-hood exhaust heat–use coated headers
15. Do not ram in but vent out hot air through hood vents

 

 

 

 Presumably this list is for people who build their compression too high for pump gas and then are trying to cope with it without melting their engine. It’s not going to help an engine with low compression. 

[Dudeland]

21 hours ago, Simeon said:

 

 

 Presumably this list is for people who build their compression too high for pump gas and then are trying to cope with it without melting their engine. It’s not going to help an engine with low compression. 

The way I read the article is that the intent was to increase compression, rather than reduce it, hence compression "boosting" moves.