Hi All,
I was going to wait to get an accurate diagnosis before posting, but needed to hear your views ASAP.
A couple of weeks ago I was out in the Vette (77 L82 manual) engine is fairly standard with performer intake, 650cfm carb, straight through pipes and headers. Was driving it quite hard and when slowing down to a stop and changing down the gears heard a slight engine knock. I limped it home at as low RPM as possible.
When started from cold its mechanically silent. When I say silent there is no mechanical noise at all. Once hot it was silent at idle but this top end type knock/rattle would come in at 2,000rpm. I never took the revs up high as I wanted to know the cause first.
Long story short all valve clearanced were perfect so I decided to pull the heads and figured a good time to upgrade if something had failed.
Striped the heads and checked everything possible - all good.
I decided to spin the engine over with no heads on with the starter motor and could hear the occasional knock as the piston changed direction. Further inspection found that when the no 8 piston is on the downstoke if pushed by hand there is play present and a knock sa this play is taken up. All other pistons are tight and solid on the up and downstroke.
I am going to pull the engine and pull the pistons out to check further. Has anyone else suffered this? Any ideas on what I could be looking at and what the causes may be?
Obviously it depends on what I find once its stripped, but being an L82 do I rebuild as it is, convert to a 383 or start over with something new?
I cant believe this has happened, alright it was never a power monster at 300hp on the dyno, but it was so mechanically sweet and silent....
Guess thats this summer in the Vette ruled out.

Lester

 

Just a quick note, if the above didnt make sense its because I have had a few beers to drown my sorrows....
I will post more info/findings when sober - Unless its bad news in which case it will be even less readble than the first post.

Lester

 

Unfortunatly stuff happens. Build up a 383 now with better components. I have seen all kinds of things happen. No reason something finally gives way. Nothing yo ucan do about it. Drink a few beers and start planning the future motor.

 

sorry to say but sounds like a rod bearing failed

 

 

I feel your pain. My stock '80 with L-48 and 41,280 miles developed a ping or knock the end of last year. This spring when I brought it out of hibernation I had it checked out. Two colapsed lifters and wiped the lobes off the cam.
Pulled old motor out and replaced it with a GMPP 350/330HO motor. Still chasing an intermittent miss at idle. It's been in the shop 10 weeks so far. I have driven 380 miles with new motor.

 

Pull the pan, pull the cap, and look at the damage.
May change out the bearing if cap and rod are not mangled.

 

The L82's are strong engines.. I've seen a stock bottom end L82 rev past 7,000 with no problems whatsoever. However, good parts can fail. If it is a rod bearing, have your crank turned .010 under throw in a new set of bearings and rings (while you're at). A good quality 383screams an easy 4-5K. If it is a rod bearing and you decide to have your crank turned, I would look into some aftermarket 195cc heads. They are little big for a 350, but would provide tremendous torque for a later 383 build.

 

If you just wore-out a rod bearing...and it didn't make a lot of 'trash' in the engine....check out the crank journal for any scoring/damage. If the crank is OK or can be salvaged by regrinding a few thousandths, fix the crank and install a new rod & bearing in #8. I'd bet there was a tight spot in that #8 rod bearing that went unnoticed during the rebuild. There's no reason to discard the rest of your work because of one repairable defect.

 

Thanks for the support guys. I was thinking the general response I would get would be 'stick a crate engine in' - Although I would love to, for me there is something about keeping the original block, even if all the internals are different.
I am going to pull the motor out (hopefully this weekend) and drop the no 8 piston out to see if I can determine how much damage and the cause of the failure.
I have been looking at complete forged rotating assemblies and they are not as much money as I thought they were going to be. Although my Vette is quite heavily modified from standard it was always nice to know it had its original block and was numbers matching. I think I will stick with my block whatever happens and depending on how much damage has been done either rebuild as it is or start palnning a 383.
I have decided that it wont be back on the road this summer so will take my time and be hassling you guys for plenty of advise and info on parts.
I will let you know how it goes with the pulling apart and see if I can get some pics up.

Thanks guys and heres to another night in the garage with a few beers

Lester

 

We have been using the Callies rotators as they are a top quality, The cranks journals are flat, round and there straight, And their Compstar rods are top of the line and come with ARP 2000 bolts.

We have been using the Maule pistons and the pistons and rings are about 525.00 set.

Ya we can buy 4340 cranks for 275.00 but when they are checked out thay are not quality and the same with the rods.

I am into more quality then using cheap parts.

Good luck with your build what ever way you go

 

.......what blockman said.....

 

Real sorry to hear your having such bad luck - have they got an idea on the cause of the missfire?

Again thanks to everyone for their replies.

I have pulled the motor and assessed the damage today. Its the no 8 big end. There is a fait amount of scoring on the shells and crank. I have pics and a short video of the amount of movement at the piston although I dont know how to post pics.... Now the question is do I get a regrind done on the crank and reassmble as is. Or do I build a 383?
I dont have alot of trust in the machinists over here in the UK. I think I would trust a rebore more than a regrind?

Blockman - Sounds like you have built a few (as the username suggests), your advise to others always seems to make sense. What sort of money would I be looking at for a bottom end of the quality your talking about?

Also if I went the 383 route could I refit my original L82 heads as a temporary measure until I free up the cash to get some new heads?

Looks like summit offer a whole host of forged bottom end rotating assemblies at the $1,800 mark, are they going to be of a decent quality or inferior at that money?

Thanks for taking the time to read this guys. I think I am over the depressed stage now and just very confused as to which way to go.


Lester

 

I would say you don't need a forged crank unless you're really going to be hard on it. I good set of stock rods with ARP bolts, forged pistons and an Eagle or Scat cast/steel crank should do the trick, all balanced of course. Those L82 heads will work fine freshened up with new springs and a valve job until you want more than say 300 or 350hp depending on what cam you use. Now all that said it might be cheaper to buy a complete bottom end assembled instead of buying all these parts AND shipping them AND paying a questionable machinist as you say to put it together. I know for a fact, that way you would have your butt in that seat much quicker and probably cheaper.

Pick some heads here, these guys know where to buy reliable motors and how to ship it cheap enough. I'd drive it over but I couldn't carry enough gas in my 14 footer.

 

Ok so I have been doing some thinking - I think 383 is the way I have got to go.
What do you guys think of these:

http://www.summitracing.com/parts/WRL-101099/
http://www.summitracing.com/parts/ESP-B12011030/
http://www.summitracing.com/parts/CMB-08-0038/

The first 2 kits have forged cranks, the 3rd kit is a Summit Value kit. I am hoping and would be happy to be producing 400hp and 400ft lbs of torque or somewhere there abouts. Do I need to spend $2,000 on the parts for the bottom end?
I would happily pick the parts individually but I will be honest and say I havent got the first idea where to start, what to look for or what would work with what. I need your help on this one guys, any light you can shed on it will be much appreciated.

Lester