The Ford Barn

barnnone51 · 03-30-2022, 04:30 PM

How much movement should a valve have in a valve guide? It appears that there is some gap causing the valve to rock back and forth. So how would you tell if it is time to change? it is very little but there is movement. I have had a lot of blow by. Thinking of up grading to later valves and adj lifters.

GRutter · 03-30-2022, 05:03 PM

I don't recall seeing any specs specific to a Model A engine, but 0.001-0.003 would be acceptable, with the larger tolerance for the Exhaust valves. More important would be how the valves are seating.
A lot of blow by would typically be attributed to rings. A leakdown test would help you to determine what's happening.

Bob Bidonde · 03-31-2022, 09:18 AM

A rule of thumb is that intake valves need a guide-to-stem clearance of .001″ to .003,″ and exhaust valves need from .002″ to .004″ guide-to-stem clearance.

Measure the guide ID's with the guides installed using a ball gage. Measure the valve stems with a micrometer of vernier caliper.

I would question any check that specifies an amount of valve wiggle because the amount of wiggle is a function of the valve guide's length plus the stem-to-guide clearance.

Brian in Wheeling · 04-01-2022, 09:45 AM

Caution:
(The following is intended to be humorous)

I once had an old Dutch mechanic tell me the clearence should be; "loose mit no slop"

Sort of a "mechanics tight" type of measurement!

Brian W.

barnnone51 · 04-02-2022, 06:03 AM

Quote:

Originally Posted by Brian in Wheeling

Caution:
(The following is intended to be humorous)

I once had an old Dutch mechanic tell me the clearence should be; "loose mit no slop"

Sort of a "mechanics tight" type of measurement!

Brian W.

Great Thanks The Dutch Man knows.. Perfectly Clear now!!

CT Jack · 04-02-2022, 08:09 AM

Sponsored Links (Register now to hide all advertisements)

Worn valve guides in a valve-in-block engine is not as critical as an overhead valve system. An overhead type would allow oil to leak into the combustion chamber causing oil consumption and smoking. Worn guides in a Model A engine can cause improper valve seating to occur over time. The main concern is the exhaust valves can begin to leak which would affect compression and thusly engine power. Installing new guides and proper honing of the valve and valve seats are super important.

03-30-2022, 04:30 PM	#1
barnnone51 Member Join Date: Apr 2014 Posts: 84	Valve Guides How much movement should a valve have in a valve guide? It appears that there is some gap causing the valve to rock back and forth. So how would you tell if it is time to change? it is very little but there is movement. I have had a lot of blow by. Thinking of up grading to later valves and adj lifters.

03-30-2022, 05:03 PM	#2
GRutter Senior Member Join Date: Sep 2017 Location: Mint Hill, North Carolina Posts: 386	Re: Valve Guides I don't recall seeing any specs specific to a Model A engine, but 0.001-0.003 would be acceptable, with the larger tolerance for the Exhaust valves. More important would be how the valves are seating. A lot of blow by would typically be attributed to rings. A leakdown test would help you to determine what's happening.

03-31-2022, 09:18 AM	#3
Bob Bidonde Senior Member Join Date: May 2010 Location: Long Island, NY Posts: 3,472	Re: Valve Guides A rule of thumb is that intake valves need a guide-to-stem clearance of .001″ to .003,″ and exhaust valves need from .002″ to .004″ guide-to-stem clearance. Measure the guide ID's with the guides installed using a ball gage. Measure the valve stems with a micrometer of vernier caliper. I would question any check that specifies an amount of valve wiggle because the amount of wiggle is a function of the valve guide's length plus the stem-to-guide clearance. __________________ Bob Bidonde

04-01-2022, 09:45 AM	#4
Brian in Wheeling Senior Member Join Date: May 2010 Location: Wheeling, WV - U.S.A. Posts: 241	Re: Valve Guides Caution: (The following is intended to be humorous) I once had an old Dutch mechanic tell me the clearence should be; "loose mit no slop" Sort of a "mechanics tight" type of measurement! Brian W.

04-02-2022, 08:09 AM	#6
CT Jack Senior Member Join Date: May 2010 Location: Hebron, CT Posts: 432	Re: Valve Guides Sponsored Links (Register now to hide all advertisements) Worn valve guides in a valve-in-block engine is not as critical as an overhead valve system. An overhead type would allow oil to leak into the combustion chamber causing oil consumption and smoking. Worn guides in a Model A engine can cause improper valve seating to occur over time. The main concern is the exhaust valves can begin to leak which would affect compression and thusly engine power. Installing new guides and proper honing of the valve and valve seats are super important.