Timing Chain Gears ???

[mvftw]

Are the Timing Chain Gears in a '78 L82 Steel or Nylon? I have to replace my water pump and figure if their nylon, there getting replaced while I'm in there. I thought they are steel.

 

[Jack]

I dunno ... but if I had to hazard a guess it'd be that the cam gear has nylon jacket. If the set is original and avg mileage ... I'd also hazard a guess it'd pay to replace regardless. Especially with 3/4 of the work to get in & out of the tcs already in the cards.
JACK:gap

 

[Dave L.]

I agree with Jack. My 81 had exactly as he stated. Replace now while your down in that area.

Dave

 

[mvftw]

Thanks, I have 91k miles, so it's a roller chain for me...

 

[matchframe]

Go for the roller chain!

 

[Jack]

I have to replace my water pump

IMHO a rebuilt w pump is false economy ... nowadays a new one is not much more than rebuilt. Get a brand name new one. Cast iron is just fine for 95% of drivers. Also, a "true roller" timing set is the ticket ... you do NOT have to get a Cloyes brand to get a GOOD true roller. Cloyes pn 93100, Clevite/Perfect Circle pn 93100, SpeedPro/SealedPower pn 2203100 and Elgin pn SS3100 are all equivalent top quality true rollers w/ dual .250” rollers & 3-keyway crank sprockets. Get a true roller of any brand & it’ll probably be the last tcs you’ll ever need for that street motor. With 91K on the motor ... there may've been a small groove worn into the harmonic damper snout by the timing cover seal. Check it closely when you get it out. Of course you're gonna change that seal ... but a seal alone won't prevent leaks if there's a groove ... but you can get a "redi-sleeve" kit at local parts house that'll refurbish the snout in less than 10 minutes ... about $5. As an alternative ... Victor-Reinz (clevite/dana) makes an extended seal that sticks out a tiny bit further so it rides on unworn part of damper snout ... it's called "extend-a-seal" ... it's pretty cheap too.

Remember to put some silicone on the lower driver side water pump bolt threads ... that ONE goes into the water jacket ... can leak if no sealant on threads.
JACK:gap

 

[mvftw]

Thanks for all the info, I'm getting a New ACDelco Alum. Water Pump & ACDelco Roller Chain. Do I have to remove the oil pan to remove the chain or just loosen the front of the pan?

 

[matchframe]

I have loosened all the pan bolts just enough to let the chain cover clear the front lip of the pan. Be careful not to tear the pan gasket, that will open up a whole new set of problems. Also, this will be a good time to replace the front seal while you have the chain cover off. Good luck with your project! :cool

Bill

 

[Stingray6974]

Yes, your cam gear has nylon coated teeth. Look at the cam gear when you pull the cover off. If any pieces of nylon are missing they will be inside the oil pump pickup screen. You will need to pull the oil pan to clean it out.

Mike

 

[Ala75Vette]

....a rebuilt vs new water pump. Let me tell my story. I have a '75 with 350, AC, & motor driven fan. I bought a new water pump from AutoZone. The pulleys scraped the water pump housing. I 'shimmed' it with washers, but it ate up the pump in no time, so I got a second 'new' water pump (different brand). It scraped the housing, too. I was nervous about keeping it, so I traded it in on a rebuilt one, which was cheaper. It didn't scrape, and I haven't had a problem since. So, guess my only advice would be: if everything goes back together with the new pump OK, you're better off with the new one. If it doesn't, try a rebuilt one that's got the form/fit to work with original clearances, etc.

 

[mvftw]

I don't get it. I saw water being throw around the fan the last couple of times I started it up. Today it's 60* here, I say later for the water pump, I have to throw some gears, just a short blast around. I end driving around for about hour and no leaks...what gives...I'm still going to replace the pump & chain.

 

[Jack]

I end driving around for about hour and no leaks...what gives...I'm still going to replace the pump & chain.

What gives ... heck you know cars are wierd & moody. Pumps'll do that sometimes ... kinda like an old flame. Don't be fooled ... when it feels like it (temps & pressures are right) you'll get it to "put out" ... problem is you can never know when it'll be in the mood. Follow your brain & not your heart ... replace with a newer model.

Now here’s bubba’s theory: W pump internal pressure is quite high on the seal side of impeller. When the t’stat is closed there’s a lotta backpressure so the coolant finds the weak water pump shaft seal & leaks. Maybe it was colder outside when you last saw is slinging coolant around the fan ... t’stat was more hesitant to open then & backpressure was high. Maybe it’s warmer these days and the backpressure is diminished more quickly.

Bubba continues: W pump pressure is lowest inside the lower neck ... just at that point where coolant approaches impeller. Because coolant boiling point is inversely proportional to coolant pressure ... the coolant can easily boil there ... and the pump impeller cavitates within the influx of superheated bubbles ... and flow throughout motor can cease. Even though a verifiably accurate temp sensor in top of motor read 195*... it boiled at the low pressure side of pump. Moral ... turn a pump fast enough or use too high flow pump ... resulting in too low pressure at lower neck ... and motor'll overheat ... dispelling the myth that pushing coolant too fast through radiator doesn't give it time to cool ... it's not the fast flow through radiator ... it's the vacuum at lower neck & resulting boiling there. Again, that's bubba's line of reasoning

The ACD stuff should be fine ... but recognize that just because it's a short pump does not mean it's got exactly the right dimensions for a vette ... vette hub-to-block flange spacing is ever so slightly different (I recall beginning about 1969 the vette hub is about 1/8" farther forward) than a "standard" short pump. Hence, sometimes problems with pulley alignments/chafing. It always pays to lay both old & new pumps on a tabletop and compare hub heights ... regardless if replacing with new or rebuilt. If the new hub is shorter there’s a quick reliable fix ... Mr Gasket water pump pulley shim kit pn 6129 ... available at parts houses/speed shops $5-$10. Both Moroso & Weiand make same kinda shim kit.
JACK:gap