Weak cyl Prob FOUND

[Don W.]

Some may recall that I posted awhile back about oil being pushed out of the dip-stick. Weellll I ran a compression ck and #1 is at 55. All others are 135-150. Did a leakdown and I can hear air coming out of the filler neck.

The funny part of this is I guess I've been running in the 11s on 5 cyls. :rotf:

Kidding aside you can hear it crank through the weak cyl when starting. Once started you'd never know anything was wrong. It runs great, pulls hard, doesn't use much oil (Maybe a 1/2 qt every few weeks depending on how much racing I actually did.) Makes no new noises.

Only way I even caught this was a couple days ago it wouldn't start. Finally did and started fine after so no clue there. But while cranking I hear it crank past the weak cyl. Otherwise I'd be merrily driving and racing on, what, 5 1/2 cyls??

I'm gonna do a leakdown on at least one more cyl for reference then??? I suppose I could pull the head and look. Could be a valve but I seriously doubt it. Haven't cut the filter yet. I'm thinking, hoping, that the cyl is OK because of the very low oil consumption and that it's just a damaged piston.

Before you ask I'm trying to find a bore-scope.

After all that, thoughts?

 

[0966Sy]

That's a shame Don, what are your AFR's at WOT? Had to be getting some detonation or preignition. Sounds like a broken ring land. One more questions; what brand Pistons? Hope the block will go one more bore. Good luck. Look on the bright side, you set a milestone.

 

[randy merritt]

Re: Weak cyl

Re: Weak cyl

Don, did you try and put a small amount of oil in the offending cylinder to see if the compression rose? As I am sure you know, if it did rise, this would mean bad rings, if not, it could be a valve problem. But, air coming out of the filler neck does not sound good.

 

[blacktyaffair]

Re: Weak cyl

Re: Weak cyl

Harbor Freight makes a functionable inspection camera that can be had for less than $80 with a 20% coupon. I have one and I love it and If you'd like to borrow it I'd have no problem sending it to you.

Once you get that cylinder pushing, you'll be in the tens! :tup:

 

[ItsMyTy]

Re: Weak cyl

Re: Weak cyl

my guess is cracked piston ring land. You probably won't be able to see it with a bore scope because it will be below the top compression ring.

 

[Don W.]

Re: Weak cyl

Re: Weak cyl

Yup, agreed on everything. This motor has had a "tick" for years. Gone through 3 rebuilds. Never changed, always there. Pistons inspected every time. Last time by a professional race engine builder. Doesn't mean somethin' didn't break though.

Pistons are SRPs, rings are Totalseal.

What's strange to me is the lack of any noise or change in oil consumption. Now if the oil ring isn't broken then maybe but ring 1 or 2? Doesn't make sense. I once broke a ring in an old 454 and sounded like the motor came apart. IE Serious rod knock was the sound, broken ring the cause.

Mixtures are 11.1-2 recently raised to 11.3. I'll get spark retard sometimes, especially at the hit but then it's never more than 2-3, usually flat-line.

We'll see. Post whatever you want. It'll be a few days before it's apart.

I still think is odd that it ran so well with one weak cyl.. Part of me wants to leave it alone. :roll:

 

[Don W.]

Re: Weak cyl

Re: Weak cyl

Finally made some progress today. I'll have the head off tomorrow which -should- reveal the issue.

 

[Don W.]

Re: Weak cyl

Re: Weak cyl

Minor update. Head is off, cyl looks perfect, although hard to tell in the pic. Head looks good as well. you can see that #1 was running different.

Problem is we can't get the front dif out so I can pull the pan. Go ahead an laugh, every way we twist and turn it hits something different. It WILL be out tomorrow even if I have to raise the motor a bit.

 

[Timbo]

Re: Weak cyl Minor Update

Re: Weak cyl Minor Update

I don't think you can get the diff out without raising the motor some. Good luck!

 

[RealFastV6]

Re: Weak cyl Minor Update

Re: Weak cyl Minor Update

I don't think you can get the diff out without raising the motor some. Good luck!

When I did the brakes and Coilovers on the Sy, I also removed the diff and changed the mounts to the poly mounts. I don't remember having to do anything weird like that to get it out. I do remember some of the bolts being a little strange to get to but I was doing it on jackstands not on a lift.

 

[Don W.]

Re: Weak cyl Minor Update

Re: Weak cyl Minor Update

When I did the brakes and Coilovers on the Sy, I also removed the diff and changed the mounts to the poly mounts. I don't remember having to do anything weird like that to get it out. I do remember some of the bolts being a little strange to get to but I was doing it on jackstands not on a lift.

This is actually nuts. I had the dif out early this year by myself. Putting it in took the both of us. Now it won't even come out. I don't get it. It's as if something has settled. Like the motor...:rotf:

In years past I've R&Rd the front dif a number of times BY MYSELF. This is not making any sense. I'll loosen the mounts tomorrow then I'll know.

Regardless, The dif will be out, the pan off and the piston out. The we will know what happened. I hope anyway.:roll:

Thanks.

 

[Syclone #1188]

Re: Weak cyl Minor Update

Re: Weak cyl Minor Update

Mine had the exact same symptoms, it was broken ring lands in the piston. I pulled the heads, it looked good till I pulled the pistons out. The #1 piston was trashed.

 

[Don W.]

Re: Weak cyl Minor Update

Re: Weak cyl Minor Update

Mine had the exact same symptoms, it was broken ring lands in the piston. I pulled the heads, it looked good till I pulled the pistons out. The #1 piston was trashed.

So #? was trashed and it made no noise? That's the strange part to me. Nice to hear someone else had the same issue though.

 

[Don W.]

Re: Weak cyl Prob FOUND

Bump for prob found

 

[RealFastV6]

A little bit of JB Weld and you should be good to go.


Sent from my iPhone using Tapatalk.

 

[randy merritt]

Re: Weak cyl Prob FOUND

Well, that would do it. Glad you found the problem, Don.

 

[Damian]

Re: Weak cyl Prob FOUND

Not near as bad as mine was, but still not good! At least it's a fairly easy fix.

 

[Don W.]

Re: Weak cyl Prob FOUND

A little bit of JB Weld and you should be good to go.


Sent from my iPhone using Tapatalk.

The welder at work is pretty good. We could weld it up, stick it the lathe, cleanup the grooves and I be on my way...

Anyway thanks all. BTW the rod bearing looked good so should be OK there. What will be interesting is to see if the tick that this motor has had forever goes away. Because it changed as the motor warmed up I'd always thought it might be a piston but like I said those pistons have been looked at before. We'll see.

 

[doyle]

Re: Weak cyl Prob FOUND

a syclone of mine had the same problem with #1 and the engine was stock. is #1 known to run lean? thanks.

 

[Quickstop [UK]]

Re: Weak cyl Prob FOUND

Is that a cracked ring land? I've never seen one before but am familiar with the idea behind it.

Can you really weld it back together? /gullible. :dunno:

Quick diagnosis! Good work!