Valve to piston clearance - Hot Rod Forum : Hotrodders Bulletin Board -- Hot Rod Forum

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

LinkBack Thread Tools
  #1 (permalink)  
Old 01-24-2012, 09:08 PM
Registered User
Join Date: Jan 2012
Posts: 1
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Valve to piston clearance

Im completely rebuilding a small journal 327 (only components re-used are the steel crank and the rods). I have .030 over 10.35:1 pistons and am in the process of selecting a cam, I have my eye on a .501 lift with 1.5:1 rocker arms (unless clearance permits 1.6:1 arms) and I'm concerned about valve to piston clearance. Is there a way to calculate clearance prior to purchasing my cam?

Reply With Quote Quick reply to this message
Sponsored Links
  #2 (permalink)  
Old 01-25-2012, 05:43 AM
DoubleVision's Avatar
Not Considered a Senior Member
Last photo:
Join Date: Oct 2002
Location: Heart Of Dixie
Age: 43
Posts: 10,733
Wiki Edits: 0

Thanks: 19
Thanked 77 Times in 71 Posts
You don't calculate piston to valve clearance, the only way to know is to check it.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 01-25-2012, 08:57 AM
Registered User
Last photo:
Join Date: Jan 2011
Location: Hopewell, Va
Age: 65
Posts: 1,684
Wiki Edits: 0

Thanks: 1
Thanked 192 Times in 179 Posts
valve to piston clearance

You list the compression of the piston. How about a part number. Sounds like a flat top piston with that compression ratio. You need to know the chamber size of your heads to determine the CR. To check the clearance the motor would have to be assembled. You would use modeling clay on top of a piston, bolt the head to the block. You could set up the valve train on the one cylinder to check the clearance. Also you could discuss this with your machinist.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 01-25-2012, 12:10 PM
techinspector1's Avatar
Last wiki edit: DynoSim combinations Last photo:
Join Date: Oct 2005
Location: Zephyrhills, Florida, USA
Age: 75
Posts: 15,333
Wiki Edits: 326

Thanks: 1,500
Thanked 2,019 Times in 1,559 Posts
I've never ordered a cam based on clearance, but I suppose you could do it if you wanted to.

Install the crank on oiled bearings and snug the caps. Install a rod/piston assembly (less rings) on #1, #7, #2 and #8 on oiled bearings and snug the caps. Don't torque anything to spec, just hand tighten to snug. Install a degree wheel and pointer on the front of the crank. Find TDC using a positive stop (strap, bolt and nut) above the piston
and mark the inertia ring on the damper if it does not co-incide with the factory notch. The ring on the damper may have rotated a little from its initial register on the hub. If you'd like to begin fresh with a registered damper, get a damper unit from these has been disassembled, clocked to TDC and reassembled with new elastomeric material. The nice thing about these rebuilt dampers is that you know they will fit your crank snout because they originally came on a running motor from the factory. I have read of considerable belly-aching from fellows who purchase new offshore units and they don't fit the crank, being either underbored or overbored.

Get a set of 8 light checking springs and set up an intake and exhaust valve in #1, #7, #2 and #8 chambers.
Slip your forefinger and middle finger under the retainer and give the valve tips a little tap with a plastic hammer to seat the locks.

Lay the heads on the block and retain them with a couple of bolts, just snugged down. You won't need a head gasket.

Set up a dial indicator
on a flat area of the retainer and preload it by 0.100". Zero the dial. Stoop down and eyeball the plunger on the dial indicator and make certain that it's parallel with the valve stem in both X and Y axes. Caution: push only on the valve tip with your finger or tool. Pushing on the retainer may unseat the locks.

Clearance will probably be tightest on the exhaust valve during the overlap period, when the piston is chasing the exhaust valve back onto its seat, so check it every 5 degrees or so, beginning at 20 degrees BTDC all the way through 20 degrees ATDC on the degree wheel.

You will undoubtedly find varying clearances from one cylinder to another. This will be due to grinding inaccuracies on the crankshaft rod journals, the rod lengths, the piston compression height differences, piston deck height differences, relationship from the block deck to the valve seats measurements, etc. This is why you have to measure every build that you put together.

Now, let's say that you find an average of 0.680" valve travel before you touch the piston with the valve head, as you push the valve tip down. If you add the gasket thickness (let's use 0.040"), you have the capability of using a cam with (0.680" plus 0.040" = 0.720") at zero clearance. If you use the generally accepted figures of 0.080" clearance on the intake valve and 0.100" clearance on the exhaust valve, then you should be able to (in an otherwise perfect world) run a cam with up to 0.620" lift without interference.
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply

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:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Please select your insurance company (Optional)


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

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
454 piston to valve clearance? turchiac Engine 7 09-09-2010 06:42 PM
piston to valve clearance? Backwoods Engine 9 06-15-2010 05:41 PM
piston to valve clearance lowandloud91 Engine 8 06-24-2009 11:51 PM
piston to valve clearance 347mustang Engine 3 05-02-2005 04:52 AM
piston to valve clearance crazyman Engine 7 02-22-2004 03:52 PM

All times are GMT -6. The time now is 02:53 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, 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 © 2017 DragonByte Technologies Ltd.
Copyright 1999 - 2012. All Rights Reserved.