1976 Riviera - Blow-by??

fancy pants · Post by **fancy pants** » Wed Jun 10, 2009 5:19 pm

I have long suspected an exhaust leak, and when I let off the gas at higher rpms there is an exhaust pop. The recording may not be the best at communicating the sound that I am hearing, but it seems to be in addition to the exhaust leak.

It does go away as the engine warms, but returns under load.

I am bringing it in to Hans on Monday to get his take on things.

spiffy · Post by **spiffy** » Wed Jun 10, 2009 6:17 pm

Gypsie wrote:
hambone wrote:That ain't good...
could be piston slap, if an engine gets overheated perpetually, the piston skirts rub against the cylinders.
Or you could have a rod(s) starting to wear out, clearance between the bearings and the crank too great.
If it gets worse under load, then you could be looking at Rebuild City. Stop in have some jo you're in good company....don't mind the mess of discarded engine cases.
But maybe have a pro have a listen-see before you do anything drastic.
Although it does sound like you have an engine near the end of it's wear cycle.
All good stuff.

I have a few cases too...(harumph....)

This'll be interesting.

As much as taking yer chances with a AAA card in hand I think the 'fam' factor calls for an immediate answer before chances are taken.

Q for the group..
Is there any way to tell if yer pistons are too close to the head while everything is together? Don't think so but one hopes....

that's where your deck height measurement comes in. If you have it whithin spec then your pistons won't "touch" anything in the head.

fancy pants · Post by **fancy pants** » Thu Jun 11, 2009 1:17 pm

To recap, symptoms are:

- loss of oil pressure at and above 240 deg (250+ occurs regularly on mountain grades)
- recent worsening of oil leak despite replacing rear seal, dipstick boot, oil cooler, push rod tube seals, breather box seal
- oil pools on top of engine, in front of fan, and appears to be coming up through dipstick (??)
- case pressure, per my evaluation, seems minimal
- compression 140-150 (~3 months ago)
- knocking (rod or other?) when cold and when under load

I am taking it in for a professional opinion on Monday. In addition to double-checking previous replaced seals and evaluating case pressure, what diagnostic tests would be useful?

Leak-down test?

Thanks!

dtrumbo · Post by **dtrumbo** » Thu Jun 11, 2009 3:35 pm

fancy pants wrote:To recap, symptoms are:

- loss of oil pressure at and above 240 deg (250+ occurs regularly on mountain grades)
- recent worsening of oil leak despite replacing rear seal, dipstick boot, oil cooler, push rod tube seals, breather box seal
- oil pools on top of engine, in front of fan, and appears to be coming up through dipstick (??)
- case pressure, per my evaluation, seems minimal
- compression 140-150 (~3 months ago)
- knocking (rod or other?) when cold and when under load

I am taking it in for a professional opinion on Monday. In addition to double-checking previous replaced seals and evaluating case pressure, what diagnostic tests would be useful?

Leak-down test?

Thanks!

Here's my .02 and it follows the "it's most likely the simplest explanation" postulate.

You have a bad and/or leaky oil pressure sender. It's worth $6.00 to rule it out.

fancy pants · Post by **fancy pants** » Fri Jun 12, 2009 4:03 pm

Thanks for the detailed response, Jim. I am new to doing my own work and need all of the help that I can get (can't wait for my visit with Colin in July!). My other problem is that I travel for work and just haven't had the time to dive in any deeper right now.

In response to your post, this is a stock '76 FI, with the exception of Petronix ignition, which I installed last summer. The gasket was glued to the breatehr box - I sill check it again when I get back into town. Also, the seal was missing from my dipstick, so I found one with the seal intact and replaced. Finally, my oil fill tube had been loose and I replaced it last month with one that seats propoerly.

I have not yet had a chance to check out the dizzy o-ring. I also appreciate the suggestion about the oil pressure sender. As I am hoping to drive the family to Maupin next weekend and have no time to get my hands dirty before we go, I will still need to bring this to a shop. I will relay all of these suggestions and cross my fingers...

THanks!

Post by **Amskeptic** » Sat Jun 13, 2009 7:03 am

fancy pants wrote:In response to your post, this is a stock '76 FI, with the exception of Petronix ignition, As I am hoping to drive the family to Maupin next weekend and have no time to get my hands dirty before we go, I will still need to bring this to a shop. I will relay all of these suggestions and cross my fingers...

THanks!

Some knocking when cold (a soft muffled knock) that goes away when the engine is warm is piston slap. Severe, it could be a collapsed piston skirt with attendant oil consumption problems past rings and excessive blow-by that promotes leaks out of all prone areas, like oil fillers and dipsticks.
ColinGETTOMISSOULABOY

fancy pants · Post by **fancy pants** » Sat Jun 13, 2009 3:15 pm

That is a good description of what I am hearing and am not sure that it really translates in the recording on the previous page. That is my biggest worry, but as a novice mencahnic, I really need someone else to listen to it before attempting the Maupin trip with a 4 year old and a 1 year old. I am bringing it in tomorrow and will let you all know the diagnosis.

On that note, Colin, if it is what I fear we will be working on a teardown in July, rather than the 101 course previosuly planned. I am nrevous, but up for the task with some guidance.

LiveonJG · Post by **LiveonJG** » Sat Jun 13, 2009 4:03 pm

fancy pants wrote:I am nrevous, but up for the task with some guidance.

It's not that bad, a great learning experience for sure. Peering over the abyss, just a bit. Look at it this way you've already got to be at least a little off balance to be driving a bus.

-John

fancy pants · Post by **fancy pants** » Sat Jun 13, 2009 8:41 pm

I thrive on being off balance...

LiveonJG · Post by **LiveonJG** » Sat Jun 13, 2009 11:03 pm

fancy pants wrote:I thrive on being off balance...

Yea, like the first night I met ya. So off balance you toppled right over!

Remember that?

-John

Gypsie · Post by **Gypsie** » Sat Jun 13, 2009 11:32 pm

fancy pants wrote:I thrive on being off balance...

Thank goodness your so good at it....

fancy pants · Post by **fancy pants** » Sun Jun 14, 2009 12:19 pm

I barely bits and pieces of that:). I do remember saving the guitar though!

Gypsie · Post by **Gypsie** » Sun Jun 14, 2009 12:57 pm

I was impressed by the guitar saving dive roll. twas a wonder.

fancy pants · Post by **fancy pants** » Tue Jun 16, 2009 6:56 pm

Alright, the diagnosis is in..... (drumroll please)

After taking it into Hans Foreign Auto today, they found that the majority of the leak ("85%") was coming from the valve covers, while the rest was coming from the push rod tubes on the left side and a small leak at the rear seal. The rear seal has never been replaced (and leak appears minimal), but the valve covers were removed by the same mechanic who replaced the push rod tube seals. I knew that the work was less than acceptable when I found a zip tie in one of the tubes. After giving him 4 chances to fix his work, the leaks apparently persist. His final assessment after my last call was that it had to be case pressure, as everything else was taken care of. Problem is, I couldn't find any evidence of case pressure, nor could Jason (at Hans' shop). It appears that the valve covers are leaking onto the heater boxes, the oil is getting inside, and then being blown around by the fan, making it look to me like the leak was on the top (damn fan!).

He never heard the knock that I hear at startup - by the time it was at the shop it had gone away.

So I guess the plan will be to replace the valve cover gaskets (which I thought would have been replaced during the initial work), and drive her out to Maupin!!!

The good news is that I have finished building my garage, so I now have a place to work and learn to do these things by myself - the right way...

See you all this weekend!

LiveonJG · Post by **LiveonJG** » Tue Jun 16, 2009 8:58 pm

Safe roads John.

-John

Itinerant Air-Cooled

Itinerant Air-Cooled

1976 Riviera - Blow-by??