# Very Low Compression **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [December 11, 2019, 7:30pm UTC](https://community.cartalk.com/t/very-low-compression/154481 "2019-12-11T19:30:54Z")\ **Posts on this page:** 10\ **Page:** 2
**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\ **Post date:** [December 12, 2019, 2:26am UTC](https://community.cartalk.com/t/very-low-compression/154481/21 "2019-12-12T02:26:10Z")
> [@warhorse5865\_150915](#): > > Was that a diesel engine with minimum 210psi? No . . . gasoline engine 1st generation GMC Canyon ---
**Author:** ![ok4450](https://avatars.discourse-cdn.com/v4/letter/o/e9bcb4/32.png) [@ok4450](https://community.cartalk.com/u/ok4450)\ **Post date:** [December 12, 2019, 7:19pm UTC](https://community.cartalk.com/t/very-low-compression/154481/22 "2019-12-12T19:19:23Z")
The general rule of thumb regarding compression on an engine in good shape at roughly sea level is 20 X the compression ratio. Drops a bit with wear and elevation. You say the other cylinders are good. What do you mean by good? I ran a compression check on my Lincoln at 275k miles while replacing plugs (4.6 DOHC) and it still carried 180 a cylinder. ---
**Author:** ![warhorse5865\_150915](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/warhorse5865_150915/32/15683_2.png) [@warhorse5865\_150915](https://community.cartalk.com/u/warhorse5865_150915)\ **Post date:** [December 13, 2019, 2:21am UTC](https://community.cartalk.com/t/very-low-compression/154481/24 "2019-12-13T02:21:16Z")
The others run in the upper 100s, at least 160 psi, never had any problem with misfiring on any cylinders except for #1. ---
**Author:** ![ok4450](https://avatars.discourse-cdn.com/v4/letter/o/e9bcb4/32.png) [@ok4450](https://community.cartalk.com/u/ok4450)\ **Post date:** [December 13, 2019, 2:27am UTC](https://community.cartalk.com/t/very-low-compression/154481/26 "2019-12-13T02:27:29Z")
Compression is decent at 160 so I agree with the partial repair. ---
**Author:** ![diazsjonathan8\_160866](https://avatars.discourse-cdn.com/v4/letter/d/85f322/32.png) [@diazsjonathan8\_160866](https://community.cartalk.com/u/diazsjonathan8_160866)\ **Post date:** [December 13, 2019, 10:33am UTC](https://community.cartalk.com/t/very-low-compression/154481/28 "2019-12-13T10:33:09Z")
Take the suggestion from expert mechanic, In few case it dangerous . ---
**Author:** ![warhorse5865\_150915](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/warhorse5865_150915/32/15683_2.png) [@warhorse5865\_150915](https://community.cartalk.com/u/warhorse5865_150915)\ **Post date:** [December 13, 2019, 2:04pm UTC](https://community.cartalk.com/t/very-low-compression/154481/29 "2019-12-13T14:04:22Z")
It’s quite possible there’s buildup around the rings as the car sat for quite a while before I bought it about a year ago. I think it might be possible the dent on the crown of the piston moved the ring out of place so I’ll be checking for that as well. ---
**Author:** ![eddo](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/eddo/32/2594_2.png) [@eddo](https://community.cartalk.com/u/eddo)\ **Post date:** [December 13, 2019, 7:50pm UTC](https://community.cartalk.com/t/very-low-compression/154481/30 "2019-12-13T19:50:31Z")
perhaps I am confused here, so help me understand if I am, but: When did you check compression on this engine? Before you removed the old head with bent valves? if you checked compression with bent valves, that is why compression was low. or did you check compression with the new head installed? and if so, why is it back off now? ---
**Author:** ![warhorse5865\_150915](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/warhorse5865_150915/32/15683_2.png) [@warhorse5865\_150915](https://community.cartalk.com/u/warhorse5865_150915)\ **Post date:** [December 13, 2019, 8:20pm UTC](https://community.cartalk.com/t/very-low-compression/154481/31 "2019-12-13T20:20:32Z")
I checked compression with the new head on, but I used an old gasket and old bolts just so I didn’t waste the new ones I have torquing everything down. I had to take it back off so I can install it with the new bolts and gasket. ---
**Author:** ![eddo](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/eddo/32/2594_2.png) [@eddo](https://community.cartalk.com/u/eddo)\ **Post date:** [December 13, 2019, 8:25pm UTC](https://community.cartalk.com/t/very-low-compression/154481/32 "2019-12-13T20:25:48Z")
I wouldn’t trust readings with an old gasket… ---
**Author:** ![warhorse5865\_150915](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/warhorse5865_150915/32/15683_2.png) [@warhorse5865\_150915](https://community.cartalk.com/u/warhorse5865_150915)\ **Post date:** [December 13, 2019, 9:24pm UTC](https://community.cartalk.com/t/very-low-compression/154481/33 "2019-12-13T21:24:22Z")
They definitely aren’t “for certain” readings with a used gasket, but for the compression readings to jump so high after a wet test indicates the piston/ring problem if I’m not mistaken. [Previous page](https://community.cartalk.com/t/very-low-compression/154481.md?page=1)