33 Buick low compression, low vacuum

[George chomokovski]

Hi every one, I have a 1933 Buick model 8-58 that I am bringing back to life after a ten year sleep. The fuel system has been cleaned  , and adjusted, points and timing set. It runs but not strong, the comp  test was 75 psi  for all eight and the best vacuum  of 14 inches at 800 feet above sea level.  All I can think of was cam timing is off.  Any one have any ideas

 

[Morgan Wright]

75 psi is not a low compression for that year. At 800 feet the atmopshere is 14.28 pounds on average.

 

http://www.carnut.com/specs/gen/buick30.html

 

Times 5.25 is 75.

 

 

[sligermachine]

Let it run for a hr. or 2   it will get better .most of the time the rings will loosen up some times .

[George chomokovski]

Well since I have the front off the engine, What is the correct method to set up the timing  marks on the cam/crank gears.  what would be the top speed of the car be, the owner said  the guy he bought it from had it up to 80. mph . This  speed has me worried as it is a long stroke engine and a fresh rebuild. 

[Grimy]

My 1934 56S (and all other 50 series that year) had 4.88 differential gears and a cruising speed of 45 mph and I might go for short bursts to 55-60, but no more than that. 

 

I think any vacuum over 16 is excellent.  Suggest you do a thorough check for vacuum leaks--do you have the vacuum-assisted brakes as mine did (or other faddish accessories like power-assisted shifting)?  If so... (1) disconnect and plug the vacuum source for the brakes, then check vacuum; (2) ensure that vacuum hose leading to the power brake unit is VACUUM heavy duty hose (about $5/ft) rather than heater hose; (3) add some castor oil to the seals in the power brake unit as per the shop manual.

[George chomokovski]

The

21 minutes ago, Grimy said:

My 1934 56S (and all other 50 series that year) had 4.88 differential gears and a cruising speed of 45 mph and I might go for short bursts to 55-60, but no more than that. 

 

I think any vacuum over 16 is excellent.  Suggest you do a thorough check for vacuum leaks--do you have the vacuum-assisted brakes as mine did (or other faddish accessories like power-assisted shifting)?  If so... (1) disconnect and plug the vacuum source for the brakes, then check vacuum; (2) ensure that vacuum hose leading to the power brake unit is VACUUM heavy duty hose (about $5/ft) rather than heater hose; (3) add some castor oil to the seals in the power brake unit as per the shop manual.

I thought 80 was B.S  for this car,   On a flatdeck maybe.  I did a vacuum leak test with all two lines plugged best I could get is a steady 13-14 inches.   Next is why I think the compression is low is the shop manual says the low compression engine is102 psi and the high compression is to be 114 so 75 is low by 40 psi  on this engine.

[Grimy]

George, check those specs again, because I think the 102/114 psi will be at 1,000 rpm rather than cranking speed.  That means running engine with gauge in one hole, 8 separate times.  Even 50 years ago, I didn't know any mechanics who did a 1,000 rpm compression test.  Rule of Thumb (ROT) for low compression engines like ours is atmospheric pressure (14.7 at sea level, calculated for you earlier in thread for your 800 ft elevation) x compression ratio.  So at sea level, OPTIMAL compression reading would be 14.7 x 5.25 = 77.18 gauge reading, and less at your altitude.

 

If the car hasn't been run recently, a good dose of upper cylinder lube in your gas tank (4 or 5 ounces of Marvel Mystery Oil per 10 gallons) will free up valves sticking/dragging in their guides.

 

One other thing to check is whether the advance weights in the distributor are gummed up by dried grease.  Also, check vacuum with the vacuum advance disconnected and the line plugged--if there's a difference, the diaphragm in the vacuum chamber may be compromised.

[Spinneyhill]

The rule of thumb for compression pressure works roughly for low compression engines. I have posted before on this, e.g.

Post number 8 and 9 in this thread:

This paper gives a formula:

Nominal compression pressure.pdf

which is

compression pressure = (pressure at bottom dead centre [usually 1 atmosphere]) * (volumetric efficiency) * (nominal compression ratio)^{(specific heat ratio of working fluid)}

  

where the specific heat ratio of petrol + air, corrected for engine heat, is about 1.3 and

  

the volumetric efficiency depends on valve timing. For your car I expect it to be ca 75% to 80%.

  

Your standard compression ratio is 5.25:1, so the compression pressure at TDC = 14.7 p.s.i. x 0.75 x 5.25^1.3 =  95 p.s.i.

  

The gauge reading will be one atmosphere less than this because the gauge reads zero under air pressure. So the gauge reading would be c. 80 p.s.i. at sea level. If the VE is 80%, gauge reading will be ca 86 p.s.i.

[George chomokovski]

The  distributor is has no vacuum advance so no problem there. The weights are free and lubed. By the way the correct name and model is a 1933 McLaughlin  Buick 8-58 ser 203179 engine 2843827

1 hour ago, Grimy said:

George, check those specs again, because I think the 102/114 psi will be at 1,000 rpm rather than cranking speed.  That means running engine with gauge in one hole, 8 separate times.  Even 50 years ago, I didn't know any mechanics who did a 1,000 rpm compression test.  Rule of Thumb (ROT) for low compression engines like ours is atmospheric pressure (14.7 at sea level, calculated for you earlier in thread for your 800 ft elevation) x compression ratio.  So at sea level, OPTIMAL compression reading would be 14.7 x 5.25 = 77.18 gauge reading, and less at your altitude.

 

If the car hasn't been run recently, a good dose of upper cylinder lube in your gas tank (4 or 5 ounces of Marvel Mystery Oil per 10 gallons) will free up valves sticking/dragging in their guides.

 

One other thing to check is whether the advance weights in the distributor are gummed up by dried grease.  Also, check vacuum with the vacuum advance disconnected and the line plugged--if there's a difference, the diaphragm in the vacuum chamber may be compromised.

4 hours ago, Grimy said:

My 1934 56S (and all other 50 series that year) had 4.88 differential gears and a cruising speed of 45 mph and I might go for short bursts to 55-60, but no more than that. 

 

I think any vacuum over 16 is excellent.  Suggest you do a thorough check for vacuum leaks--do you have the vacuum-assisted brakes as mine did (or other faddish accessories like power-assisted shifting)?  If so... (1) disconnect and plug the vacuum source for the brakes, then check vacuum; (2) ensure that vacuum hose leading to the power brake unit is VACUUM heavy duty hose (about $5/ft) rather than heater hose; (3) add some castor oil to the seals in the power brake unit as per the shop manual.

I thought 80 was B.S  for this car,   On a flatdeck maybe.  I did a vacuum leak test with all two lines plugged best I could get is a steady 13-14 inches.   Next is why I think the compression is low is the shop manual says the low compression engine is102 psi and the high compression is to be 114 so 75 is low by 40 psi  on this engine.

[Spinneyhill]

23 minutes ago, George chomokovski said:

shop manual says the low compression engine is102 psi

Do they state the engine speed? Cranking or 1000 r.p.m.?

 

Note that the formula I gave above gives an absolute compression pressure of 102 p.s.i. for compression ratio of 5.25 and VE of 80%.

 

Your gauge reads zero at 14.7 p.s.i. = atmospheric pressure, so subtract this amount from 102 and you get the gauge pressure reading = 87 p.s.i..

 

Was the engine run in before it went to sleep for 10 years?

 

Is this of interest?

https://support.alldata.com/article/tech-tip/running-compression-tests

Edited June 2, 2018 by Spinneyhill (see edit history)

[George chomokovski]

No to engine speed . the 102 is for the low compression engine the 5.25 ratio is 114 for compression and the  running comp test  would be lower than a cranking test as in the sample test below. Last all I know is the car has less than 300 miles since purchase in 1999 , last plate is 2008

Sample Test Readings

Comparing measurements between cylinders is important. Running compression at idle should be 50-75 PSI (about half cranking compression). Snap throttle compression should be about 80% of cranking compression. Let’s analyze the results from the following sample test readings.
 

EXAMPLE 1
CYL	STATIC	IDLE	SNAP
1	150	75	85
2	175	80	130
3	160	75	120
4	160	80	120

In Example 1, cylinder #1 has a snap test reading that is much lower than the other cylinders. If a snap reading is low (much less than 80% cranking compression), look for air intake problems such as severe carbon deposits on intake valves, worn cam lobe,worn valve guides and springs, rocker or push rod problems, or “shutter valve” miss-positioned in the runners of a variable runner intake system.

Edited June 3, 2018 by George chomokovski
more info (see edit history)

[Grimy]

At this point, since you have the front cover off (if I understand correctly), I think you should assure yourself that the timing marks are correctly aligned per the shop manual, then rig up the radiator even if a temporary method, and EXERCISE the car, driving it somewhat hard but not flogging it.  I'd expect some loss of compression from ten years' disuse--sticky rings and valves.  So I'd drive the car initially as if breaking in a new engine:  full or almost-full throttle from 20 to 40, then let it coast on compression back to 20, repeat 10 times.  All this with thin oil such as 5W-20 or straight 20.  Do about 100-200 miles and change oil HOT.

 

The GREAT news is the even compression across all cylinders.  Compression may come up after this treatment.  By the way, how confident are you in the accuracy of the compression gauge you've been using?

[George chomokovski]

That is the trouble, the manual doesn't give the proper method of setting or checking the cam timing . I only have the front cover off , the rad is still in place.  the timing marks on the gears do not line up at TDC, but they are alined  just not At TDC . this is is dot to dot . but there is a line on the cam gear that is three teeth off from a letter C on the crank with the crank at TDC. My comp tester does get used {about weekly} and is accurate.   Every time I have come across this low compression /low vacuum the cam had jumped a tooth or two. It's the timing marks that have  me stumped. This car is fighting me, the gas gauge drove me nuts, when it was rebuilt they painted the inside of the housing which is needed for a ground. And the sending unit was not grounding because of a gasket between the upper and lower portions of the unit.

[Grimy]

This is the "fun" of sorting a car out.  Remember that the crank gear will make two revolutions for every one of the camshaft gear.  You may need to rotate the engine and use a mirror to see the marks--not pleasant.  Think about taking the valve cover off so you can watch the sequential operation (lift) of the valves.

 

Have you had the car running?  Does it run well?  Ignition timing checked?

 

We'll try to help, but please be patient as we don't know a lot of things about THIS car yet.

[George chomokovski]

First ,  yes valve cover , yes to running, run well not so much. smooth enough ,but lack of power. I will give you a run down on work done. Gas tank cleaned and sealed , electric pump had a dead spot from sitting , so it was removed and run {in fuel not dry}  till it would pump on demand fuel filters replaced, carb cleaned and adjusted as per manuel. Plugs cleaned and gapped, points cleaned and adjusted ,distbuter cleaned and lubed, valve lash checked and the timing has been adjusted by timing light test light and by vacuum gauge. Fuel pressure checked. air filter cleaned .

[Grimy]

Hi George, thanks very much for the list of work performed to date.  I now understand why you're looking at the timing gears, and also your apparent frustration.  Are you using the Buick shop manual?  Mine went with my car 10 or more years ago, so I'm stuck with a MoToR 1935-46 manual.  The '35 engine is the same as yours except for having 1/32 more bore.  Here's the minimal amount the MoToR manual has to say (and the timing gears changed in 1936):

 

"1935 Series 50-60-90: Normal gear backlash is from .0005 to .001.  Excessive backlash may be reduced .001 inch by using replacement camshaft gears designated as Plus 1S, which have teeth .001" thicker at the pitch circle than standard gears.  If this gear does not reduce the backlash to normal, the complete set of gears should be replaced.  NOTE:  When installing timing gear, be sure the timing marks are meshed."

 

As expected, the bulk of the information pertains to 1936 and newer.

 

To me, the important information here is that the marks be meshed, because on newer cars (1936-46), an illustration shows the cam gear mark at "2:30 o'clock" and the crank gear about "2:45 o'clock," with a specified 10 links or 11 teeth between the marks.

 

If you're NOT using a Buick shop manual (1934-35 Series 50-60-90 manual will also work), let me know and I'll dig into my archives for a National Service Data manual--but can't do so until Monday at the earliest.

 

Best wishes!  You'll find it!

[George chomokovski]

Yes Grimy, I am using the 1933 McLaughlin Buick shop manual. If I remember right the three gear timing was only on the 31-33 model years .In 34 they changed to a gear and chain, and the dist was driven off the cam and the generator was belt driven. or a completely different casting. But as you say the change over could be in 36. If I could verify the cam timing  is correct then I will reassemble the engine and as you and sligermachine have  said run it. I have had it running for about an hour, with about 6 miles on the road. It was on the road where you notice the lack of power and the slow revving under load. But at 86 hp who knows.  Oh ya I think I remember a timing mark on the flywheel when the dots on the crank and cam are alined but it is not at TDC

Edited June 3, 2018 by George chomokovski (see edit history)

[Grimy]

Well, the timing mark on the flywheel will come up to the pointer twice, once correct and once 180* out.  Since the car runs reasonably decently except for low power, you might want to bring the TDC mark (is it for #1 or another cylinder?) up while watching the valves on that cylinder.  Then look at the timing marks to see how far off they are.  Consider checking the timing instructions in the manual carefully to note which marks are the ones you can use, and again, which cylinder.  You may well be a couple of teeth off.

[George chomokovski]

There are three marks on the flywheel , one where the timing marks line up. This is not TDC.  Then the next is the advanced timing mark then a few degrees later TDC. The marks are all within 1/4 crank rotation. As I have the valve cover off{to see overlap} as well as the distributor  cap {to check rotor position}  and the engine runs I can't be out 180 . A friend sent me a screen capture of a forum conversation that said just line up the timing marks on the cam and crank bring it to TDC line up the distributor to number 1 start and set the timing. As for the manual I have it has one blurry pic of the timing gears and no instructions. I will take some pics tomorrow witch may help.

Edited June 3, 2018 by George chomokovski
cant answer post (see edit history)

[Bloo]

There is a 1933 Buick manual on OldCarManualProject, and like the McLaughlin manual you describe, it has a blurry picture of the gears and neglects to mention how to time them. There is, however, a diagram of the valve opening/closing events for all models, and unlike many manuals I have seen they tell what lash and how much lift the measurements were taken at.

 

It should be possible to set the intake valve at .008, and with #1 on the overlap, look for the intake valve to open just barely before TDC (4 1/2 degrees). It could be a bit late due to gear wear, but you should be able to count the teeth on a timing gear and calculate how many degrees a tooth is worth, I'll bet a lot, and probably enough to show if the valve timing is wrong.

 

http://www.oldcarblog.com/manuals/1933/1933 Shop Manual/page1.html

 

 

Edited June 3, 2018 by Bloo (see edit history)