engine compression? - Alfa Romeo Bulletin Board & Forums
Reply
 
LinkBack Thread Tools Display Modes
post #1 of 35 (permalink) Old 02-17-2015, 01:35 PM Thread Starter
Registered User
 
JimPunkrockford's Avatar
 
Join Date: Mar 2012
Location: hawaii
Posts: 107
engine compression?

sorry for the new thread, but i'm having trouble "searching".

what should my compression be on a 1968 1750 spider motor?

thanks in advance
JimPunkrockford is offline  
Sponsored Links
Advertisement
 
post #2 of 35 (permalink) Old 02-17-2015, 01:58 PM
Trained (ex)Professional

1953-2018 RIP

Platinum SubscriberAdministrator
 
papajam's Avatar
 
Join Date: Feb 2003
Location: New Jersey USA
Posts: 16,232
IMO, anything north of 160-ish is good. More important than actual numbers though is that all the cylinders are within about 10% of each other (some say 15%).

Jim

Series 2 USA 1750 GTV (in Series 1 European clothing)
papajam is offline  
post #3 of 35 (permalink) Old 02-17-2015, 10:17 PM Thread Starter
Registered User
 
JimPunkrockford's Avatar
 
Join Date: Mar 2012
Location: hawaii
Posts: 107
Quote:
Originally Posted by papajam View Post
IMO, anything north of 160-ish is good. More important than actual numbers though is that all the cylinders are within about 10% of each other (some say 15%).
thanks. so i am sub 110 but all within 10% and no blue smoke.

would it be safe to assume i need a valve job?
JimPunkrockford is offline  
Sponsored Links
Advertisement
 
post #4 of 35 (permalink) Old 02-18-2015, 01:01 AM
Registered User
 
GTA R's Avatar
 
Join Date: Dec 2010
Location: Yorkshire, UK.
Posts: 837
Garage
Sub 110 ? Are you doing the test with the engine hot and with the throttle wide open ?

Steve

GTA R
1963 Giulia Ti Super Rep
GTA R is offline  
post #5 of 35 (permalink) Old 02-18-2015, 06:02 AM
Richard Jemison
Platinum Subscriber
 
Alfar7's Avatar
 
Join Date: Apr 2005
Location: Pensacola, Fl. U.S.A.
Posts: 7,043
Static Compression

Quote:
thanks. so i am sub 110 but all within 10% and no blue smoke.

would it be safe to assume i need a valve job?
Not at all. Static compression readings reflect several engine conditions but the chance of having all the valves leaking "evenly" is less than miniscule.

Since the motor isn`t smoking that says the oil control ring and 2nd ring are still wiping oil off the liners adequately.

With your discription my suggestion is to check your engine`s cam timing.
If the cam timing is off it will likely reduce the static CR.

One of the "urban myths" scattered by many sources was the added power from advancing the intake camshaft and retarding the exhaust cam a couple of degrees.
This might help but only at high RPM. In fact moving the cams in such a manner increases an already excessive amount of overlap killing low and mid-range torque/HP. The stock cams are not not going to reflect much power change at all due to their mild profiles.

Advancing cam timing needs to be clarified. Advancing the intake cam (clockwise) opens the valve earlier and retarding the exhaust (counter clockwise) closes the valve later. Both increasing overlap, reducing torque and reducing engine efficiency and reducing the static CR #s you get when checking the engine with a guage.

To be clear these 1750 engines came with camshafts timed at various points LC wise depending on whether Euro carbed models, or USA versions with variable intake timing. If it was a spica car it had the vvt unit and the timing was to be at 114 int (100 when advanced above 1700 RPM) and 102 exh.

Alfa issued a TSB changing weber carb`d versions to 104 / 104 in the `70s.
The Euro 1750 used a larger lift version of their standard lobe design, and LCs were set at 99.5/99.5.. The drivability of these cams improved as well when reset to 104/104.

If your car has Carbs now, set the cams to 104/104 LCs and recheck the CR. Should be a bit higher and drive much better.

If it still suffers the Spica curse, set the cam timing on the exh side to 104 and make sure the intake side is not less than 114. If it`s a bit outside the 114 mark (cam mark to the intake side of the cap mark) that won`t hurt either.

If there is leakage issues the only way to determine where the compression is going is with a leak down test.

Richard Jemison
RJR Racing

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

"When you are dead you don`t know it.
Only those around you are distressed.
Same with stupid"

Last edited by Alfar7; 02-18-2015 at 06:08 AM.
Alfar7 is offline  
post #6 of 35 (permalink) Old 02-18-2015, 08:00 AM
Registered User
Gold Subscriber
 
rogerspeed's Avatar
 
Join Date: May 2005
Location: OC CA USA
Posts: 3,585
Quote:
Originally Posted by Alfar7 View Post

...If it was a spica car it had the vvt unit and the timing was to be at 114 int (100 when advanced above 1700 RPM) and 102 exh...
Richard, you are confused. No 1750 SPICA motors came with VVT.
As far as I know VVT start with the 1982 l-jet 2.0 spider

current:
84 Spider Veloce
ex:
To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

solve problems, learn something new!
rogerspeed is offline  
post #7 of 35 (permalink) Old 02-18-2015, 08:01 AM
Registered User
 
Join Date: Jun 2014
Location: MI
Posts: 216
Garage
Quote:
would it be safe to assume i need a valve job?
It would be safe to assume nothing. Keep in mind a compression test doesnít tell the whole story of an engines health and people often get hung up on the compression number. Typically if all compression values are within 10% then the engine passes the compression test. If you suspect you have a head problem I would do a leak down test.

Jason
'79 Spider
ljayr is offline  
post #8 of 35 (permalink) Old 02-18-2015, 08:03 AM
Registered User
 
101/105guy's Avatar
 
Join Date: Apr 2005
Posts: 6,590
Roger....
Back away from the keyboard slowly......

'64 Guilia Spider
'67 GTV
'68 Giulia Super

Conservatives-we work hard, so you don't have to !
101/105guy is offline  
post #9 of 35 (permalink) Old 02-18-2015, 08:11 AM
Registered User
 
Join Date: Apr 2003
Location: Denver, CO
Posts: 346
It may be that your gauge may is reading low. I've got 2 gauges and they read about 15psi apart. If your engine runs OK, you're not using oil and the relative readings are close then there's probably nothing that needs to be done.

Mitch
MitchW is offline  
post #10 of 35 (permalink) Old 02-18-2015, 09:27 AM Thread Starter
Registered User
 
JimPunkrockford's Avatar
 
Join Date: Mar 2012
Location: hawaii
Posts: 107
Quote:
Originally Posted by MitchW View Post
If your engine runs OK, ..... nothing that needs to be done.
unfortunately the engine runs terrible. but i like your optimism

Quote:
Originally Posted by ljayr View Post
If you suspect you have a head problem I would do a leak down test.
i guess that would be the logical thing to do. then i can narrow this down. is there a thread about how to do a proper and comprehensive leak down test?

Quote:
Originally Posted by Alfar7 View Post
With your discription my suggestion is to check your engine`s cam timing.
If the cam timing is off it will likely reduce the static CR.
this has also been suggested in the past, i guess a leak down test first would be in order. but how would i go about checking cam timing? is there a thread or a book or something?

as always, all of this help is greatly appreciated
JimPunkrockford is offline  
post #11 of 35 (permalink) Old 02-18-2015, 11:03 AM
Senior Member
Platinum Subscriber
 
alfaparticle's Avatar
 
Join Date: Oct 2004
Location: Columbia SC
Posts: 12,958
Quote:
As far as I know VVT start with the 1982 l-jet 2.0 spider
It was introduced in 1980 on Spica 2L Spiders.

Ed Prytherch
79 Spider
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
alfaparticle is online now  
post #12 of 35 (permalink) Old 02-18-2015, 12:13 PM
Registered User
 
101/105guy's Avatar
 
Join Date: Apr 2005
Posts: 6,590
As always,
pictures of the offending motor would settle this.....

And as far as running poorly,you can spend the next year (some have !) going from suggestion to suggestion, changing parts and spending $$ or you can do what a competant mechanic would do.....
Trouble shoot each system in a logical order.
There are several books with this M.O. and it will save you time, money and grief.

'64 Guilia Spider
'67 GTV
'68 Giulia Super

Conservatives-we work hard, so you don't have to !
101/105guy is offline  
post #13 of 35 (permalink) Old 02-18-2015, 12:38 PM
Registered User
 
Join Date: Jun 2014
Location: MI
Posts: 216
Garage
Quote:
is there a thread about how to do a proper and comprehensive leak down test?
I dont know, but there are some good YouTube videos on the subject. I would recommend that if you are not familiar with the leak down test to get a friend or find a mechanic who is. A miss diagnosis could be very costly.

Jason
'79 Spider
ljayr is offline  
post #14 of 35 (permalink) Old 02-18-2015, 12:48 PM
Moderator
Platinum SubscriberModerator
 
Alfajay's Avatar
 
Join Date: Jan 2005
Location: San Juan Capistrano
Posts: 9,841
Quote:
Originally Posted by GTA R View Post
Sub 110 ? Are you doing the test with the engine hot and with the throttle wide open ?
JimPunkrockford's answer to GTA R's question (which was asked way back in post #4 ) would take us a long ways toward answering the original question.

Readings of 110 psi would be low for a warm engine with the throttles open. But if cold/closed, 110 doesn't sound so bad. So, which is it?

Jay Mackro
San Juan Capistrano, CA

'65 Guilia Sprint GT
'67 Duetto
'91 164L
Alfajay is online now  
post #15 of 35 (permalink) Old 02-18-2015, 01:55 PM
Del
Senior Member
Gold Subscriber
 
Join Date: May 2005
Location: seattle
Posts: 15,348
Don't forget to dribble a little oil into each cylinder when doing the compression check. If you don't do this, you can end up with low readings.

Del

Seattle

1989 Milano, Shankle Sport
1991 164S, stock
1994 164LS (~Q)
1972 Morgan 27

previously owned since 1964:

62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6
Del is online now  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Alfa Romeo Bulletin Board & Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in













Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome