L20b intake problems

[datsun77]

i am on my 2nd motor in my 77 620. i had to replace the intake gasket on the original engine after i bought it. now my intake gasket is leaking on the engine i have in it now. i have a couple of friends that have had the same problems.does anybody know what causes this or is this a factory defect

[datzenmike]

It isn't a common problem but tightening some of the lower mounting bolts on the L20B is. Also, the '77 had the intake and exhaust bolted together didn't it? Any chance the plate between then has corroded from the exhaust?

 

Did you use any kind of sealer on the gasket surface? Are you using a header?

[Llittle_Llama]

i just did the L16 intake swap and in addition to replacing the gasket, i replaced all 8 of the bolts and washers, made installation MUCH easier and torquing 10X faster, i would start by replacing the bolts.

[datsun77]

the intake and exhaust were together.i am not using a header and i did not use gasket sealer.the engine in my truck now is a 1980 L20b with the same problem as the 77 engine had the intake is sucking air near the head.

[datzenmike]

Well, if leaking, best to replace it to be sure. If any of those studs or bolts are rusty you may not be getting full clamping force when tightening. Replace like dwnshifter suggests or at least wire wheel them as clean as you can and put a dab of engine oil on them. Some of the bottom bolts have a thick washer that clamps intake AND exhaust so be sure they are on.

 

Are you sure the vacuum leak is at the head and not between the two manifolds? Both the intake and the exhaust share a common opening with a thin metal divider sandwiched between them to warm the intake air. Doesn't take muck for a pin hole to corrode through.

[Llittle_Llama]

hey datzenmike, under those conditions would you recommend doubling up the gaskets? i know you cannot if they have the brass ring around the water ports though.....

[datsunfish]

The only time I have ever had intake leaks at the head was with a severely overused gasket.The lower bolts are a serious bitch especially with the L20b stove pipe setup.This is were headers pay off.Gear wrenches,long thin wrenches and socket wobblers are great too.

[Llittle_Llama]

weeble wobble extensions FTW!

[datsunfish]

"FTW"you mean for the win right?:DThere was a discussion about that a while back.The other meaning is not as fun.

[datsun77]

thanks for all the suggestions i will keep them in mind when i pull the intake.right now i have to get it moving my clutch is shot.has anyone put a clutch in a 620 lately is there enough room to un bolt the trans and slide it back to put the clutch in or is it easier to pull the engine and do it???

[420n620]

I dont believe u will have anuff room to work on it. When I replaced my clutch set up, I pulled the engine and tranny @ the same time. I also dropped the idler arm, only 2 bolts hold it. Datsun must have used a shoe horn to get them into the engine bay, there just enuff room to get engine/trans out/in together. Dont forget to plug the end of the trans to save the fluids. good luck :D

[datzenmike]

To help with the trans leakage just drain over night. The bung at the very bottom of the tranny has to come out and looks just like the filler one on the side. The bottom bung has a magnet on it so inspect it for chunks. A Black metallic 'paste' is normal. Wipe it off clean for next time you inspect. Any time the tranny comes out CHANGE the oil, it's cheap, you have the old oil out now anyway so do it. To re-fill is easy. Once tranny is installed, get a couple of feet of heater hose, or the largest hose that will fit the filler hole, and run it down past the shifter boot. Get a small funnel from a dollar store and put in the top end and start pouring in NEW gear oil. Have someone watch when it's full and pop your bung into your hole (yeah I said that) If you have decided to switch to a synthetic, replace the rear tranny spline seal first because this stuff is so slippery it will squeese past an old seal. The seal is $6 so change anyway and is easily tapped in with the flat of a 2X4 and a hammer.

[datsunfish]

I can change the clutch in my 620 by dropping the tranny but I have a short shaft dogleg that has a ton more clearance than the long ones.I am pretty sure you can still do it though.A bit of a PITA but maybe better than dismounting the motor.

[Llittle_Llama]

I can change the clutch in my 620 by dropping the tranny but I have a short shaft dogleg that has a ton more clearance than the long ones.I am pretty sure you can still do it though.A bit of a PITA but maybe better than dismounting the motor.

 

short shaft = 5 speed?

[datzenmike]

The '77-'79 200sx had a dog leg shift pattern, short tail stock 5 spd (about 26" long) It fits perfectly into a 510 car which had a short 4 speed too.

 

The '72.5-'73 620 trucks had a short tail 4 spd in them so a short dog leg would 'drop' right into them without changing the drive shaft. Interesting.... I just looked and datsunfish does have a '72.5 620.