Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > Porsche 911 Technical Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Registered User
 
Join Date: Nov 2004
Location: Eastern WA.
Posts: 113
Question Compression Test using impact wrench to turn engine instead of starter?

It has been suggested to me that I can perform a compression test by cranking over the engine with a impact wrench on the crank pulley bolt. Is this an acceptable way to turn the engine for compression testing?

Reason for the question: Engine is out of the car, separated from the transmission / starter, and on a engine stand, pretty much stripped down to the long block. I performed a leak down test while the engine was still in the car (with all losses in the 5-7% range), but did not do a compression check. I guess at this point the compression test would simply be to test valve spring effectiveness. My visual inspection of and manual pressure on the valves / springs / retainers revealed nothing of concern (albeit to my relatively untrained eye).

So, impact wrench to turn the engine over? Yes, or no?

Thanks, Gary S.

Old 12-19-2010, 05:34 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Registered
 
Join Date: May 2003
Posts: 3,320
I don't think this would work, nor would it accomplish anything. You might over tighten the bolt big time or even break it off. As the compression came up the gun would just twist in your hand or turn the motor over too slowly to do any good. If you have good leak down and no broken valve springs (inspect visually) then there is no point.

-Andy
__________________
72 Carrera RS replica, Spec 911 racer
Old 12-19-2010, 05:42 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Registered
 
Join Date: Oct 2001
Location: San Carlos, CA US
Posts: 4,872
if there is a choice between compression test and leak down test, and you can only have one, then leak down test is the one to have.
__________________
Porsche 2005 GT3, 2006 997S
Exotic: Ferrari F348TB Factory Challenge, Ferrari 328 GTS
Disposable Car: BMW 530xiT, Audi A3S
Two-wheel art: Ducati 907IE, Ducati 851
Old 12-19-2010, 06:42 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
83 911 Production Cab #10
 
JJ 911SC's Avatar
 
Join Date: Jun 2009
Location: Ottawa, Ontario, Canada
Posts: 11,058
Garage
And you drained the oil out?
__________________
Who Will Live... Will See

83 911 Production Cab #10, Slightly Modified: Unslanted, 3.2, PMO EFI, TECgt, CE 911 CAM Sync / Pulley / Wires, SSI, Dansk Sport 2/2, 17" Euromeister, CKO GT3 Seats, Going SOK Super Charger
Old 12-19-2010, 06:51 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Platinum Member
 
dad911's Avatar
 
Join Date: Jul 2001
Location: Leave the gun. Take the cannoli.
Posts: 15,793
Doesn't sound like a good idea to me. If you really want to check compression, bolt up transmission, flywheel, and starter. Won't take long.

Why is the engine out/stripped? Are you rebuilding it?
Old 12-19-2010, 06:58 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Registered User
 
Join Date: Dec 2010
Posts: 4
This will not work. You'll end up breaking the bolt.
Old 12-19-2010, 07:30 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Registered User
 
Join Date: Nov 2004
Location: Eastern WA.
Posts: 113
Quote:
Originally Posted by Eagledriver View Post
I don't think this would work, nor would it accomplish anything. You might over tighten the bolt big time or even break it off. As the compression came up the gun would just twist in your hand or turn the motor over too slowly to do any good. If you have good leak down and no broken valve springs (inspect visually) then there is no point.

-Andy
Thanks Andy. Mostly I agree with you. The only point would be to verify my visual inspection.

Quote:
Originally Posted by dad911 View Post
Doesn't sound like a good idea to me. If you really want to check compression, bolt up transmission, flywheel, and starter. Won't take long.

Why is the engine out/stripped? Are you rebuilding it?
dad911, thanks for the input. I'm trying to locate the source of a clacking sound (see audio / video link below). I had several 911 owners come listen to the engine and got various opinions ranging from exhaust leak, valve train noise, and rod bearing. In initial attempts to correct, I pulled off the SSI's and did a valve adjustment, checking for broken valve springs as I went along. Put the SSI's back on with new gaskets at the exhaust flanges and the muffler. Changed oil and filter, fired it back up, still clacking. Did the leak down, results as mentioned above. Next pulled individual plug wires at the coil sequentially and listened for changes. The clacking sound was still evident when the plug wire was pulled for 1, 2, 4, 5 and 6. However, it quieted noticeably when the plug wire for cylinder 3 was pulled. The fellow who suspects a rod bearing cited this information as the basis for his suspicion (no spark to smack a rod with a bad bearing against the crank journal). This seems like the most likely cause to me at this point, but I want to eliminate as many other potential causes as possible before a complete teardown.


Quote:
Originally Posted by JJ 911SC View Post
And you drained the oil out?
Yes, the oil is drained out, other than the residual surface coating. And the plugs are pulled. And the clutch / pressure plate and flywheel have been removed. As well as the CSI system, fan / alternator, shroud and wiring harness. As mentioned earlier, basically down to the long block.

Here is a 45 second video of the engine at slow (warm) idle with the clacking sound clearly audible:

slowest idle video by brg2290 - Photobucket


And lastly, some additional info. The day this clacking sound began, I had already driven the car at city speeds for 20 minutes or so. No unusual noises, and the car was warmed up nicely. I stopped at a stop sign waiting to enter a 60 mph highway. The sound began as soon as I accelerated onto the highway.

Gary S.
Old 12-19-2010, 09:08 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Registered
 
T77911S's Avatar
 
Join Date: Oct 2006
Location: MYR S.C.
Posts: 13,785
a compression test will not tell you if you have a broken valve spring or a bad rod bearing.

you did not say what year your car is, nor how many miles are on it. the 3.2's dont have the best reputaion when it comes to rods.
__________________
86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 12-20-2010, 05:58 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Registered User
 
Join Date: Nov 2004
Location: Eastern WA.
Posts: 113
Quote:
Originally Posted by T77911S View Post
a compression test will not tell you if you have a broken valve spring or a bad rod bearing.

you did not say what year your car is, nor how many miles are on it. the 3.2's dont have the best reputaion when it comes to rods.
The car is a '78 SC with the original 3.0. It has 152,000 miles on it. In 2004 broken head studs called for a teardown and subsequent installation of ARP head studs. New main bearings done at the same time, but according to my paperwork, not rod bearings. The work was done by a local P car mechanic with years of experience, including dealership work at Vasek Polak (which doesn't make him infallible, just for reference).

I never intended to use a compression test to check the rod bearing. Knowing that the leak down numbers were all good, why wouldn't a poor compression number indicate the possibility of weak or broken valve spring(s)?

Gary S.
Old 12-20-2010, 09:16 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
Registered User
 
Join Date: Nov 2010
Location: Hartford CT
Posts: 14
First- I don't believe an impact wrench will work when doing a compression test.

Second - If its a bad valve spring your looking for - forget it. The compression test won't tell you that.

There are a couple of test that could illustrate weak or broken valve springs if the motor were in the car and running. Aside from that - a broken spring could be determined by visual inspection. A weak spring - you need to disassemble and test each spring individually on a spring compression tester.

Good Luck-
Old 12-20-2010, 09:32 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #10 (permalink)
Registered User
 
Join Date: Nov 2010
Location: Hartford CT
Posts: 14
I listened to your video and read in further detail about plug number 3. I would expect a connecting rod bearing to have a little higher pitched sound - but having the noise go away upon removing the plug wire is a "classic" symptom of bad con rod bearing - or a bad wrist pin
Old 12-20-2010, 09:43 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #11 (permalink)
Registered
 
Join Date: Nov 2008
Location: Huntington Beach, CA
Posts: 492
Garage
You can attach a starter to your motor with a starter adapter ring from Zalex Industries.



Although, I agree with the others....a leak down test is better.
Old 12-20-2010, 01:28 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #12 (permalink)
Actual Porsche owner
 
wdfifteen's Avatar
 
Join Date: Mar 2008
Location: SW Ohio
Posts: 24,625
Garage
Quote:
Originally Posted by brg2290 View Post
T

I never intended to use a compression test to check the rod bearing. Knowing that the leak down numbers were all good, why wouldn't a poor compression number indicate the possibility of weak or broken valve spring(s)? Gary S.
Weak springs usually manifest themselves at higher RPM because a weak spring doesn't have enough force to close the valve quickly. Even a proper compression test would not be conclusive because the engine isn't turning fast enough to tell if a valve is a little slow in closing. Besides, springs don't suddenly get weak. The DO suddenly break, but you can tell that with a visual inspection.
__________________
.
Old 12-20-2010, 02:25 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #13 (permalink)
Registered User
 
Join Date: Nov 2004
Location: Eastern WA.
Posts: 113
Quote:
Originally Posted by 911Gedward View Post
First- I don't believe an impact wrench will work when doing a compression test.

Second - If its a bad valve spring your looking for - forget it. The compression test won't tell you that.

There are a couple of test that could illustrate weak or broken valve springs if the motor were in the car and running. Aside from that - a broken spring could be determined by visual inspection. A weak spring - you need to disassemble and test each spring individually on a spring compression tester.

Good Luck-
Thanks. Based on what I'm reading here, I'm going to nix the compression test altogether.

Quote:
Originally Posted by 911Gedward View Post
I listened to your video and read in further detail about plug number 3. I would expect a connecting rod bearing to have a little higher pitched sound - but having the noise go away upon removing the plug wire is a "classic" symptom of bad con rod bearing - or a bad wrist pin
A wrist pin would seem to be an easier repair to accomplish. Either way, with a clack that loud, I'm thinking I should be able to tell if it's one or the other once the cylinder is pulled.

Quote:
Originally Posted by tperazzo View Post
You can attach a starter to your motor with a starter adapter ring from Zalex Industries.

Although, I agree with the others....a leak down test is better.
Nice tool, looks expensive!

Quote:
Originally Posted by wdfifteen View Post
Weak springs usually manifest themselves at higher RPM because a weak spring doesn't have enough force to close the valve quickly. Even a proper compression test would not be conclusive because the engine isn't turning fast enough to tell if a valve is a little slow in closing. Besides, springs don't suddenly get weak. The DO suddenly break, but you can tell that with a visual inspection.
Okay, makes sense, and thanks for the explanation wdfifteen.

So, I'll forget about the compression test. Since cylinder #3 was indicated as the likely source of the sound, for now I think I'll focus dis-assembly on that bank.

Again, thanks to all who've posted.
Gary S.
Old 12-20-2010, 04:36 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #14 (permalink)
Registered
 
Join Date: May 2003
Posts: 3,320
It does sound pretty bad. I don't think it sounds like a rod knock however. I've heard a rod knock and it's a much lower thumping/knocking sound. I do think you'll have to start taking it apart to get to the bottom of it.

-Andy
__________________
72 Carrera RS replica, Spec 911 racer
Old 12-20-2010, 09:02 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #15 (permalink)
Registered User
 
Join Date: Nov 2004
Location: Eastern WA.
Posts: 113
Quote:
Originally Posted by Eagledriver View Post
It does sound pretty bad. I don't think it sounds like a rod knock however. I've heard a rod knock and it's a much lower thumping/knocking sound. I do think you'll have to start taking it apart to get to the bottom of it.

-Andy
Hi Andy. Yup, I started getting into it more last night. Basically, just removed the chain tensioner oil lines and cover plate on the left side of the engine, then had to send out an email locally to locate the 46mm crowfoot wrench and holding tool for the cam nut. One of the local PCA fellows has them, so I won't be stuck for too long as I can pick them up today.

Gary S.
Old 12-21-2010, 08:58 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #16 (permalink)
Registered User
 
Join Date: Nov 2004
Location: Eastern WA.
Posts: 113
Update - Spring 2012

So, over a year later, here's an update. This may come in handy for others searching for solutions to clacking noises. Short story - disassembled the engine. Paid a local Porsche mechanic (Richard Buechler - Alpine Motors) to come to my garage and look over the various parts of the engine to see if he could pinpoint the source of the knock heard on the video. Nothing definitive was noted. Continued with an extensive refurbishment of the engine, including: micro-polish crank, re-size rods, rebuilt heads with new valve guides, new main, rod and intermediate shaft bearings sent to Calico Coatings for treatment, lots of new parts from Pelican and clean, clean, clean as per Wayne's book.

Richard did the reassembly for me, and one day during the reassembly I received a phone call from him. He said, "I think I found the source of your engine noise, and you're not going to be happy." I asked what he thought it was. He said that, while rotating the engine on the stand at just the right angle during assembly, he saw an open air injection tap below one of the exhaust ports. Back in 2004 I had eliminated the OEM cast iron exhaust and air injection lines by back dating the exhaust to SSI's. I was told that the mechanic who did the work apparently used NPT plugs and Loctite to plug the air injection ports, even thought the ports are metric threads. One of the plugs had blown out, and this is where the clacking sound had been coming from! In hindsight, my engine did not need to be disassembled.

But at the time of this discovery we were well on the way to having it all back together. This was January, 2012. Here are some pictures of the engine.

Gary S.





Old 04-15-2012, 08:17 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #17 (permalink)
Registered User
 
docrodg's Avatar
 
Join Date: Apr 2009
Location: Cape Vincent, NY
Posts: 841
At least he did nice work. Looks gorgeous.
__________________
1968 911S "Leona"

Air goes in and out, blood goes round and round, any variation on this is a bad thing.
Old 04-16-2012, 12:12 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #18 (permalink)
 
Registered
 
Join Date: May 2006
Location: Snohomish, WA
Posts: 1,607
Garage
Gary,

Beautiful engine - if that's any consolation. When I replaced my air injectors, the experts suggested NPT plugs. But I used the correct metric thread ones which can be found for 914 brakes:

Pelican Parts - Product Information: PEL-BRC-02

I know it's disappointing, but it was most likely dirty or oily threads that kept the thread locker from working. I'll double check my plugs next time I'm under the car.

__________________
Rex
1975 911s and 2012 Range Rover Sport HSE
1962 BMW R50/2, 1995 BMW R1100RS, 1948 Harley FL

Last edited by Walter_Middie; 04-16-2012 at 12:41 AM..
Old 04-16-2012, 12:18 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #19 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 12:21 AM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2020 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.