Compression test results on '67 +2

[Johnfm]

Bought the car on Sunday.

Did compression test tonight (dry). Did each cylinder twice and got the following (with throttle at WOT):

#1: 196
#2: 197
#3: 179 and not holding pressure as well as the others
#4: 203

Seem reasonable to me.

I suppose I need to figure out why 3 is lower and leaky...

[mbell]

Those are roughly inline with the results from my +2 big valve. It was also lower on three. My thoughts were weak spring from it been Sat for number of years. Plan to recheck it once I've run it for a while.

[john.p.clegg]

It's only a two minute job to test No 3 wet which will tell you lots...

John

[Johnfm]

Yes - I will do it again this weekend.

I assume I just need some sort of squirter to get a bit of oil into the cylinder?

[john.p.clegg]

Yep,round the edge of the piston if you can...

John

[promotor]

Bought the car on Sunday.

Did compression test tonight (dry). Did each cylinder twice and got the following (with throttle at WOT):

#1: 196
#2: 197
#3: 179 and not holding pressure as well as the others
#4: 203

Seem reasonable to me.

I suppose I need to figure out why 3 is lower and leaky...

I'm guessing either rings or valve seats and/or tight valve clearance(s). If your valves aren't seating properly the oil down the bores will not only help get a seal on broken rings, but also hide the effect of badly sealing valve seats slightly. I've seen cracked valve seats show a bad result on a compression test and improve with oil down the bores

Have you checked your valve clearances?

[elanman999]

Have you checked the tappet clearances? Just because it's quiet does not mean they are correct.

Edit, sorry Promotor, I should have fully read your reply before posting
Cheers
John

[Johnfm]

No, not checked.

I have only had it since Sunday and been too keen to drive it every evening just to get things warm, check for problems etc.

Will I need a new cam cover gasket if I remove it to check clearances etc?

[john.p.clegg]

Yes and No,you will probably destroy the old one on removal but with a little silicone and grease/vaseline/oil you can make a re-useable gasket.....

Thoroughly clean the cam cover gasket face and apply a thin bead of silicone ,lightly oil the head gasket face and place in situ,leave overnight,next morning trim any excess gasket off and fit the nuts and tighten...

in future you should be able to remove the cam cover and replace without needing new gaskets...

John

P.S. I use my thumb and forefinger as an inverted V to spread the silicone evenly

[Johnfm]

Bought the car on Sunday.

Did compression test tonight (dry). Did each cylinder twice and got the following (with throttle at WOT):

#1: 196
#2: 197
#3: 179 and not holding pressure as well as the others
#4: 203

Seem reasonable to me.

I suppose I need to figure out why 3 is lower and leaky...

I'm guessing either rings or valve seats and/or tight valve clearance(s). If your valves aren't seating properly the oil down the bores will not only help get a seal on broken rings, but also hide the effect of badly sealing valve seats slightly. I've seen cracked valve seats show a bad result on a compression test and improve with oil down the bores

Have you checked your valve clearances?

Good call on the valve clearances. Checked them tonigh:

BACK OF ENGINE
Inlet (mm) Exhaust(mm)
4 .15 to .2 .2 to .25

3 .05 to .1 .15 to .2

2 .15 to .2 .2 to .25

1 .05 to .1 .1 to .15

So, #1 and #3 inlet valve and #1 exhaust clearances out of spec - all those out of spec not having enough clearance.

Strange that cylinder #3 inlet has similar lack of clearance to #1 inlet, yet #1 had strong compression numbers.

looks like I need to de-shim those three valves. May as well put some fast road cams in if I have to pull them to adjust clearance...

[promotor]

Those figures are a bit tight but as you say it's strange that similar figures give a different compression result.

I'd be inclined to think that there is another problem on top of the clearances. Might be worth holding off getting new camshafts until you've got the shims set correctly on the existing ones and re-test the compressions. - you don't what what you'll find, it might change your mind on what cams to use etc. Maybe that's a little bit of my belt-and-braces approach coming through!

[MickG]

Hi Jon.
I'm a little confused by your readings probably because they are in mm and not thou. How have you got two readings for each valve clearence? The feeler either fits or it dosnt.
The cold valve clearences in my manual are as follows
Inlet 005/007. .(127/.177mm)
Exhaust .009/.011 (.228/.279mm)
So generally for standard cams the inlets are .006 and the exhausts are .010
Some others my disagree but I have mine set as above and my engine is as sweet as a nut

Mick G

[Johnfm]

The reading are the range - in that the lowest number would fit in teh gap, and teh upper number wouldn't - so the clearance is somewhere between the two.

My smallest feeler gauge is 0.05mm.

I need to buy some smaller gauges if I want to measure with greater accuracy - but as it is, it has indicated the three 'tight' ones.

[MickG]

Hi Jon,
Thanks for the reply I thought that was the case although I couldn?t be sure.
Is there any chance you could give the readings in thousandths of an inch as I think they would be more recognisable to us more senior members.
Check the clearances as you have been doing, if say 6 thou fits and 5 thou doesn?t then the clearance is 6 thou.
You only need accuracy to 1 thou as the shims are graded in one thou increments. Most suppliers use thousandths of an inch as a unit of measure anyway.

Regards Mick G

[MickG]

Hi Jon,

Just spent a few minuets converting your metric readings to imperial and I have come up with the following:-

.................................Inlet.......................Actual...........................Ex .....................Actual
Cylinder 4........... ......6 - 8.........................7..............................8 ? 10......................9

Cylinder 3 .................2 ? 4.........................3..............................8 ? 10......................9

Cylinder 2 .................6 ? 8.........................7..............................8 ? 10......................9

Cylinder 1 .................2 ? 4........................ 3..............................4 ? 6........................5

Check my figures I used a conversion programme found on the internet.

Given that the valve clearances are 6 thou inlet and 10 thou exhaust with a + or ? of 1 thou you can see clearly that No 1 is very tight both inlet and exhaust and No 3 Inlet is also very tight.
Check you measurements again and make sure they are correct. I check mine at least twice

Ps sorry about all the dots it was the only way I could format it.

Regards Mick G