Hey all, haven't had my '86 running in quite a while, and getting the itch to start driving it again.
Adjusted the valves yesterday (cold) and started it up this evening just to get it going.
When it warms up and idle drops down to aroung 1000, the truck shakes quite a bit.
The motor sounds smooth (no obvious misfire or popping sounds), so I'm wondering if the motor mounts may be the culprit?

Thoughts?

Thanks in advance!

Todd

My experience with engines starting to shake at idle was from a valve starting to burn causing low compression in one cylinder.

Might do a compression test to make sure you don't have a weak cylinder for whatever reason.

And since you just adjusted the valves, might recheck the clearances.. Too little clearance on a valve on one cylinder?

When I adjusted the valves, it seemed that all were tighter than spec. I didn't check to see what they were to begin with though.
I'll have to do a compression test and see what I get. Any way to do that by yourself?

Thanks,

Todd

Well, compression test says 150, 150, 0, 0.
I can hear the air rushing from 3 to 4 when testing 3, and 4 to 3 when testing 4.
Starting the teardown now. Waiting for the coolant to drain overnight, and will continue tomorrow after work.
Hope it's just the head gasket, but I'll find out more as things progress.

Thanks!

Post a photo or 2 when you get it opened up......

Here it is.
Obviously the head gasket blew between 3 and 4, but I don't see much else in terms of damage.
Would too tight of valve clearances have played a part in this failure?
To me, looks like the head is OK, but I appreciate any suggestions.


Block overall...


Block between #3 and #4...


Head overall...


Head between #3 and #4...


Thanks!

Todd

Well, on further inspection, looks like #3 piston got a bit of shrapnel from the HG failure, and #4 has a gouge in it, presumably from the same.
Also, as I was feeling along the cylinder wall, I could feel a slight dent in #3 near the top next to the failure.
Not sure what caused all of this, but I'm thinking it's time to pull the rest out.
I have another motor that's been sitting for a few years. Need to go through that one and get it ready to drop in.
Oh the joys!
<img src="/forums/images/graemlins/cyclops.gif" alt="" />

Todd

Ouch. You might run a magnet thru the oil pan when you drop it to see if the thrust bearings are laying in there. Had that do some interesting stuff in the past. The crankshaft will have a lot of longitudinal slop in it. IIRC, with the thrust bearings in place, the max play is something like 4mm.

No worries on that, not reusing the short block.
The pan will be cleaned out before it gets transferred to the new short block.
Unfortunately, the second head I have has a cam bolt hole that is stripping out - as I was torquing it down it became easier to turn. Not good.
I'd rather not reuse the original head because I noticed some surface issues in the compression area.
Seems to me a potential place for pre-ignition problems.
Someone local has a head for sale. I think I'll pick that one up and use it.
As usual, trying to keep costs down.

<img src="/forums/images/graemlins/cyclops.gif" alt="" />
Todd