Head inspection, valve problems, ETC

[DaveyDaveDaveDave]

So I have a stock 77 with a u67 head. It lost a valve lash pad (not the first time, but first time on this valve) I put it back where it belongs, got everything looking just like it should. I have zero compression, cylinder 1. The valve was cylinder 1 exhaust. Ive heard some times the valve seat can drop and shatter, its possible the valve is bent, and there are a few other theories I've heard.

 

What Im really asking is if theres a way to replace a valve without removing the head.

 

I kid.

 

What Im really REALLY asking is for input/advice on any way to look into this without pulling the head. Ive peeked in the spark plug hole best I can. Cant see shit, really. Ive cranked the engine w/ the cover off, everything lines up fine, moves fine. Is there anything else worth trying/investigating w/o head removal?

 

 

[ggzilla]

Use a leak down adapter.

[banzai510(hainz)]

re adjust the valve lash. most times if your loosing compression its the exhaust valave seat that sinks over time and youll have to adjust the rocker lash.

If lash good then valve may be cracked.

 

I have tons of lash pads if needed

 

 

open the valave cover and cran the motor with the coil wire off and ck out cyl 1 wats its doing.

sure wire and plug are good?

[DaveyDaveDaveDave]

Theres no pressure to detect leakdown on. this cylinder is barely moving the needle on a compression check.

 

Checked clearance cold, .010 between cam and rocker arm w/ lobe pointing about straight up. just a little bit of wiggle, about the same as the other rocker arms on currently closed valves.

 

Wire and plugs are good, when I crank it w/ valve cover off, i dont see it doing anything different at all from the other valves. everything is lined up right, springs are on, no signs of unusual wear.

 

I guess what Im not understanding is if adjusting lash will do anything if the valve is already coming up as far as the spring will take it.

[datzenmike]

Too much lash can cause the lash pad to fall out. If you have clearance between the cam and the rocker, the valve is closed. Now check the intake. If there is clearance then it's assumed the valves are closed and should be sealing.

[Sealik]

Theres no pressure to detect leakdown on. this cylinder is barely moving the needle on a compression check.

 

 

 

A leak down test will tell you were the problem lies...regardless of the "no pressure" on compression check.

...<.....Piston/rings, valve not seating correctly........... or..................HG

 

Intake valve...air out of carb

Exhaust valve....air out of tail pipe

Rings......air out of crankcase

HG........air out of rad or another cylinder

 

Here's a leak down test on my LZ......90lbs in...holding at 87+lbs

Excellent numbers.

Edited December 5, 2013 by Sealik

[datzenmike]

What Doug is saying is that if the intake valve is not sealing you will hear the air escaping by listening over the carb. A bad exhaust valve or seat will be heard at the tail pipe.

[DaveyDaveDaveDave]

Totally missed the point of a leakdown test :geek: . Gonna do that asap.

[EricJB]

Without spending the dough on a leakdown tester, you can modify a sparkplug to accept an air fitting, charge the cylinder with air and look for the leak.