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Discussion Starter · #261 ·
I just measured shoulder to base on PRT. I'm getting an average of 3.427" on the intake and 3.417" on the exhaust. It would be nice if they were identical, huh? And it varies a bit around the circumference. I suppose that makes it close enough to be equivalent to the 71-2576 at 3.415"?
 

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Hi Daryl,
shoulder to base on PRT
average of 3.427" on the intake and 3.417" on the exhaust
varies a bit around the circumference
nice if they were identical
Obviously not MIL-TFD-F1 ...

close enough to be equivalent to the 71-2576 at 3.415"?
Wonder if "varies a bit around the circumference" makes 'em more or less oil-tight in certain positions ...

Regards, :rolleyes:
 

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Discussion Starter · #263 ·
I've decided there's too many variables as it sits. I really need to install the tappet blocks to literally get a good base line.

What I learned from installing just a top o-ring on the PRT is that you have to do that by installing the o-ring in the head, not the o-ring on the PRT. When it came apart, the o-ring stayed up in the head. If installed the other way, the o-ring doesn't necessarily get pushed into it's recess in the head. There's two "steps" in the recess and putting the o-ring in the deepest step puts it where it should be. If it ends up on the lower step, it's less snug in the gap. The correct result allows for a lot of vertical possibilities for the PRT. It goes into that o-ring as far as it gets shoved into it, but not necessarily to the shoulder of the PRT unless the lower bit takes up enough space. So, the blocks will go in and will reassess the gaps.

Just for information purposes, the PRT o-rings I removed are in vastly different condition. I'm not sure I would know the cleaned up intake o-rings were not new. The leaking exhaust top one is hard, black, and crumbling and the other is slightly better but also obviously past it's use by date. The discrepancy is astounding.

For the tappet block install I am planning on: oil on the block before installing, rubber lube (p-80) on the o-ring, triple check the alignment is square to the bores while install. Anything I'm missing or strong opinions to the contrary? 🙏
 

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Hi Daryl,
For the tappet block install I am planning on: oil on the block before installing, rubber lube (p-80) on the o-ring, triple check the alignment is square to the bores while install. Anything I'm missing or strong opinions to the contrary?
Couple of thoughts:-

. If the tappet block O-rings are Viton (they should be), they're by definition oil-resistant, so special rubber lube isn't necessary - the oil (or grease?) and P80 are going to get mixed anyway, so imho save the P80 for jobs that need it?

. "alignment is square to the bores" - you mean each tappet guide block is square to its bore in the cylinder block, not the cylinder bores?

:sneaky: There are a couple of other factors that could be considered when installing TGB:-

. either the centre of the hole for the locking screw is perpendicular to a line through the centres of the two tappet holes;

. or the 'twist' an off-perpendicular hole imparts to the TGB matches the difference between the centrelines of the two cam lobes, which aren't necessarily at exactly 180 degrees to each other ...

... :whistle:

Hth.

Regards,
 

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Discussion Starter · #265 ·
That's very helpful. By square to the bores, I was implying aligning a line across the tappet holes centers with the cylinder bores centers. I had not really thought that a 'twist' could be desirable. There are wear marks on the tappet shafts that I will look at to see if I can figure out where the "middle" is or should be.
 

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Discussion Starter · #266 ·
I have installed the tappet guide blocks without any drama.

I'm totally fascinated by how everything is lining up now that they are in place. With the old intake o-rings to mock it up, the PRT/o-ring piece has the latitude to move up and down between the TGB and the head. The top o-ring stays up in the head and the bottom is in it's recess in the PRT. And the whole thing, with the old head gasket in place, has about 0.04" (that is on the outside, probably less of a gap inboard) of space to move in. Where it was previously, and where it would end up regardless of where it started, is with the chrome bottom of the PRT resting on the TGB and therefore the top o-ring about 0.04" above the collar of the PRT.

From what I can tell from the in situ pics I took before disassembling (not definitive as the grime gets in the way), it looks like that's where it was previously. One of the takeaways from this is that the PRTs should not be putting any pressure on the head/cylinder as they are floating between the two on the o-rings.
 
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