U20 head bolts

[mikeb]

Hi everyone,

I'm working on the car again. Out of curiousity, I pulled the cam cover and discovered that all of my head bolts with the exception of one have the early style smaller heads. I have at least two complete sets of headbolts with the later style larger heads. Would it be okay to carefully replace them one at a time without affecting the head gasket seal?

As always, I appreciate everyone's expertise and input.

Thanks!

Mike

[SLOroadster]

I think, if you correctly untension the headbolts, in reverse sequence, with the engine dead cold, you should be okay. You have to actually break the seal, so if done correctly, you should be able to pull them out and replace them, without worrying about a future head gasket leak. I will caution you to be very careful and gentle. Reduce the torque on the head incrementally, the same way, you torque the head, so, 65, 45, 25, and 0. (I might be off on those torque settings, going off memory.) Set your new bolts in, retorque in proper sequence.

Will

[mikeb]

Thanks, Will - I appreciate the advice. That makes sense to do it in reverse order. One more question: If I understand correctly, I should remove them all in reverse order and do a fresh install of the replacements per factory specs?

Mike

[redroadster]

No that's not the re torque way either
Replace loosen 1 bolt at a time , in the correct secession .
you will crack/ move the gasket loosening all the other bolts tight hold down the area around the one replaced , do it cold

[mikeb]

Okay, so one at a time. I see the point about the gasket moving around and then needing to do a new head gasket install, which I obviously want to avoid.

Thanks, everyone!

Mike

[SLOroadster]

No that's not the re torque way either
Replace loosen 1 bolt at a time , in the correct secession .
you will crack/ move the gasket loosening all the other bolts tight hold down the area around the one replaced , do it cold

The issue here is, you could end up with uneven torque across the head. The reason there is a pattern to torqing a head is so that all the bolts come up to the correct torque evenly. Doing it one at a time you have 10 different bolts torqued to value which could be very different once you have made it through. The toque readings could be all over the place.

I've found that a good head gasket will remain sealed when cold with all the bolts removed. I have always needed to smack the head with a dead blow hammer to get it to come free. That said, I've always used NIssan head gaskets. Hard to say whether or not you will have the same results. Both techniques have their potential for issues. Either one might be fine, or could cause a head gasket failure down the road for different reasons.

I've pulled my head a number of times (Never to replace a blown head gasket.) and every time its required a smack from a dead blow to pop it free once the bolts were removed.

Will

[mikeb]

Will, I've had the head off several times and you're right. It's always required a good smack from a rubber mallet or a dead blow. Thanks!

Mike

[jrusso07]

Three questions

1) Why not run the small head bolts until you need to remove the head? Is there catastrophic failure condition you are trying to avoid?

2) Would it be correct to remove each bolt in reverse sequence and replace it one at a time but only snug the bolt down (not to final torque)? Then torque to final value in sequence after all bolts have been snugged down?

3) Why not just remove the head and replace the gasket?

[spl310]

What are the dimensions of the head bolts so that I can figure out what I have.

[mikeb]

I have to pull the motor to replace the transmission front seal anyway, so I thought I would do what I could to make it worry free. I ordered one of Jim T's upper race chains, and am going to replace the head gasket and install the later style Nissan head bolts. It's not like I'm planning on abusing the motor, I just want to make it less prone to future failure, if that makes sense. It's also one of those "while I'm there, I might as well things..."

The smaller head is 15.75 mm and the larger one is 17.75 mm.

Mike

[jrusso07]

Makes sense Mike. I did the same when I had to replace my transmission. Did the timing parts, exhaust header and a new head gasket and all clutch parts - while I was there. Got the timing parts from JT.