Cam timing question on SBC 350H - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans Advertise
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Hotrodding Basics
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 11-05-2018, 06:28 AM
29fordcoupe's Avatar
Registered User
 

Last journal entry: Working suspension now.
Join Date: Sep 2017
Location: texas
Posts: 114
Wiki Edits: 0

Thanks: 62
Thanked 21 Times in 17 Posts
Question Cam timing question on SBC 350H

Hello all,

So this is basic, and probably kinda dumb... but here goes.

The previously running 350 in my 29 coupe had noisy timing gears in it.
I replaced them with some quiet ones as follows:

I rotated the crank shaft to TDC on #1. With spark plug out and used a breaker bar on the crank pulley nut and rotated crank until I could feel compression coming from the driver's side front cylinder. (#1). Then verified with a screw driver that the piston was at the top.

When I checked the timing marks on the gears that were installed, Both the timing mark on the cam, and the timing mark on the crank gear were at 12 oclock. Kinda new to sbc, I didn't think much of that, just assumed that's the way timing gear timing marks lined up on sbc.

I removed and replaced the timing gear set without turning the crank or cam. (To be honest both moved a bit, but definitely not more than a few degrees back and forth)

Looking through an sbc rebuild book this morning, I was reading the section on cam timing and saw the timing marks are supposed to be lined up at 6 oclock on the cam, and 12 oclock on the crankshaft. My engine is not completely back together yet, and I haven't fired up, so I quickly **** a brick, paniced and yelled WTF. I went back and re-read the installation instructions for the timing gear set, and verified it also saud set to set the cam timing mark at 6 oclock, and the crank timing mark at 12 oclock.

I'm trying to figure what is going on.

The timing cover, balancer, and water pump are already installed, I want to avoid removing them to verify whether timing is correct or not, if at all possible.

It just seemed to me, if I didn't turn anything while replacing them, the timing would be correct, but I can't understand why the timing marks don't line up, unless I actually had the #1 at TDC on the exhaust stroke instead of the compression stroke, but I don't see how that's possible given that I felt compression at the spark plug hole while turning the crank.

Thoughts anyone?


    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 11-05-2018, 07:44 AM
Fang16's Avatar
Registered User
 

Last journal entry: Project change
Join Date: Mar 2010
Location: Rogers, Ar.
Posts: 794
Wiki Edits: 0

Thanks: 32
Thanked 57 Times in 55 Posts
If u didn't move anything it's all ok. Worst that can happen is distributor would be 180 out.
Reply With Quote Quick reply to this message
The Following User Says Thank You to Fang16 For This Useful Post:
29fordcoupe (11-05-2018)
  #3 (permalink)  
Old 11-05-2018, 11:33 AM
Greg T's Avatar
Music and Hot Rods
 
Join Date: Jul 2007
Location: Escanaba, MI.
Age: 66
Posts: 1,725
Wiki Edits: 0

Thanks: 243
Thanked 119 Times in 101 Posts
I always set them up so that the cam mark is @ 6 oclock and the crank @ 12. Once it's together I rotate the engine 1 revolution to make them 12 and 12. THAT is when you line up the distributor and install it pointing at #1. If you leave the marks at 12 and 6, you can point the dist at #6 and all will be okay. I just prefer to make them 12 and 6 and point the rotor at #1.
Reply With Quote Quick reply to this message
 
  #4 (permalink)  
Old 11-05-2018, 11:47 AM
chasracer's Avatar
True Hotrodder
 
Join Date: Oct 2018
Posts: 645
Wiki Edits: 0

Thanks: 55
Thanked 150 Times in 133 Posts
Before you took it apart IF you had rotated the engine one more revolution, the marks would have been lined up at 6 oclock on the cam and 12 oclock on the crank. This IS the usual method of installation for the gears. The fact that you installed them the way you removed means everything is just fine.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 11-05-2018, 10:45 PM
techinspector1's Avatar
Member
 
Last wiki edit: DynoSim combinations
Join Date: Oct 2005
Location: Zephyrhills, Florida, USA
Age: 77
Posts: 16,984
Wiki Edits: 326

Thanks: 1,920
Thanked 2,831 Times in 2,118 Posts
The Chevy engineers could have made it so much easier on everybody if they had just made the marks on the sprockets so that 6 PM on the cam sprocket and Noon on the crank sprocket was firing on #1 cylinder. But they didn't. They made it so that it was firing on #6 cylinder and you had to rotate the crank 360 degrees clockwise to get around to #1 cylinder firing, showing Noon on the cam gear and Noon on the crank gear. You may be able to figure it out a little better by looking at the firing order 1-8-4-3-6-5-7-2. Four cylinders fire in each revolution of the crank, so that it takes two complete revolutions of the crank to fire all eight cylinders. Cylinders 1 and 6 both have the piston at top dead center at the same time when you put the pulleys on at cam 6 PM and crank Noon, but #6 is at ignition and #1 is at overlap. Then, when you turn the crank 360 degrees clockwise, #6 is at overlap and #1 is at ignition.
Reply With Quote Quick reply to this message
The Following User Says Thank You to techinspector1 For This Useful Post:
AutoGear (11-06-2018)
  #6 (permalink)  
Old 11-05-2018, 11:23 PM
Registered User
 
Join Date: Apr 2007
Posts: 12,594
Wiki Edits: 0

Thanks: 220
Thanked 1,200 Times in 951 Posts
The Ford Yblock had both gears at the 90 degree position pointing to your right when standing in front. Then you verified this by counting I think it was 12 chain pins between pip marks.

Then International Harvester V8's used number 3 to time the ignition, there's probable a guy out there that got a tune up job on one of these as a kid and still hasn't got it running.

Count your blessings that the Chevy is only a little goofy.

Bogie
Reply With Quote Quick reply to this message
The Following User Says Thank You to BogiesAnnex1 For This Useful Post:
AutoGear (11-06-2018)
  #7 (permalink)  
Old 11-07-2018, 08:44 AM
29fordcoupe's Avatar
Registered User
 

Last journal entry: Working suspension now.
Join Date: Sep 2017
Location: texas
Posts: 114
Wiki Edits: 0

Thanks: 62
Thanked 21 Times in 17 Posts
Thanks for all the replies.

My general OCD wouldn't let me continue assembly without checking it.
So I took it all apart and rotated it to check the timing marks at 6 and 12.

From the input here, and talking to a couple of machine shops and a mechanic, If I had lined it up perfectly at 12 and 12, it actually would have worked fine.

But the Machine shop guy asked me "Did you use a straight edge to line it up"
I had to say "NO"

He told me to check it, could easily be a tooth off if you didn't line it up with a straight edge.

I checked it and it was a tooth off.
Now its lined up at the timing marks at 6 and 12, and perfectly aligned with a straight edge.

So when in doubt, just check it again.
Well worth a new timing cover gasket, and water pump gaskets for the peace of mind.

Thanks again for all the input.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 11-07-2018, 01:23 PM
Registered User
 
Join Date: Apr 2007
Posts: 12,594
Wiki Edits: 0

Thanks: 220
Thanked 1,200 Times in 951 Posts
GM alignment is with both pip marks at the 12 o'clock position. The use of a straight edge for checking is fraught with problems since the surfaces between the marks are not smooth and the distance long, so it can be difficult to see an error.

My method, and I think you'll find plenty of supporters here, is to install the cam ready to fire number 6 instead of number 1. That puts the crank gear pip mark at 12 and the cam gear's pip at 6 o'clock which is facing each other making it easy to see the alignment especially with clockable crank gears that offer before, at , or after TDC choices. As long as you remember what you did you can just put it back together but position the distributor cap and rotor for firing number 6, but the cap wiring is conventional starting with number 1 in the factory chosen scheme. If you are concerned about forgetting where everything is after you put on the timing cover then after setting the gears with pips facing each other give the crank one complete turn so both pips are at 12 o'clock and it is set to fire number one then install the distributor and cap in the GM position. Although the intake may not be on for awhile the distributor dropped in and possibly ties down will give you visual indicator of where the crank is.

Bogie
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 11-09-2018, 09:56 AM
Registered User
 
Join Date: May 2008
Location: ohio
Posts: 3,669
Wiki Edits: 0

Thanks: 279
Thanked 514 Times in 436 Posts
Glad to hear you got it checked and fixed
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 01-08-2019, 05:30 PM
29fordcoupe's Avatar
Registered User
 

Last journal entry: Working suspension now.
Join Date: Sep 2017
Location: texas
Posts: 114
Wiki Edits: 0

Thanks: 62
Thanked 21 Times in 17 Posts
follow up.

Took me awhile to get back here, but I ended up pulling git back apart and resetting the timing marks as suggested. The piece of mind doing this was worth it. Fired right up, cam timing is perfect.
Thanks for all the input.
Reply With Quote Quick reply to this message
The Following 2 Users Say Thank You to 29fordcoupe For This Useful Post:
64nailhead (01-08-2019), AutoGear (01-09-2019)

Tags
cam timing, sbc, timing gears

Recent Hotrodding Basics posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last 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:
Insurance
Please select your insurance company (Optional)

Log-in



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
SBC roller cam conversion - cam buttons & timing covers 75gmck25 Engine 7 04-12-2018 03:53 PM
Need help with SBC cam install (timing marks question) Zeeb Engine 9 02-20-2011 10:53 PM
sbc timing question and carb question.....i am ready to absorb your knowledge c_cham Engine 16 02-12-2011 12:26 PM
Timing Timing Timing bigcountry1009 Hotrodding Basics 6 01-20-2009 06:47 PM
Help with timing Chain and timing cam install LXZ590 Engine 7 12-08-2006 11:01 PM


All times are GMT -6. The time now is 08:59 PM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.