Cam caps - replacement cams & plastiguage

[WMarshy]

Just one thought, its not worth finding out if the damaged cams will perform or not!

[KA1J]

Heh, as an experiment, no. I definitely don't want to carve new water but If someone knows from experience if that kind of damage to the lobes is negligible and creates no long term negatives, that would be good to know.

I couldn't find a good complete head/cams/valves at a price I could afford so I am trying to reuse the old head & that's why I bought these replacement cams. I just don't feel great about putting used cams into a used head even though the plastigauge showed them to be WNL. If that one caps spacing were like all the rest I'd feel better. It was within the specs but showed more cap/cam gap than any of the other caps. All the others were on the tighter end of normal and #1 exhaust was looser in gap.

It's too bad that Yama didn't elect to put replaceable bearings in there like they did with the crankshaft...

[CaptonZap]

Howdy,

If it were me, I would take a stone in a Dremel and smooth off the edges of the chipping, put it back together and run it. A 45 deg bevel around the edge would be peachy. Both edges if they are chipped. The surface area that is lost is not going to be an issue in the total scheme of things.
Better grades of cams come with the edges chamfered, and if you wanted to be anal, you could do that to all the lobes.
What you do not want is any little piece of cam coming off after you put it back in. Think "breaking off a piece of cookie" and there is always a crumb that does not come off with the piece, but falls off after you set the cookie down.
That piece is what you want to make sure is not left on the cam.
Which would include a good solvent rinse after the grinding is done.
DO NOT touch the face of the lobes, with any abrasive, of any sort.
Lots of oil on reassembly.
You'll be golden,
CZ

[petejw]

swapping cams out isnt a problem for the head as long as the cams are in spec ull b good 2 go, if u can, ideally use the cam caps that come with the head.

[KA1J]

There is an order listed in the book. IIRC it is cap # 3-4-2-5-1 that is off the top of my head but pretty sure it is correct but if I am wrong someone please correct me.

I've been looking but darned if I can find the order listed. O'course the manual has real omissions like not mentioning the ring bevels facing up on #2 ring in the assembly section, & that detail was only alluded to in a drawing under "Engine maintenance" in section 7 & no mention of it was made.

So... It's entirely possible I've missed where they hid the torque sequence detail.

[KA1J]

swapping cams out isnt a problem for the head as long as the cams are in spec ull b good 2 go, if u can, ideally use the cam caps that come with the head.

I'm trying to understand what makes the most sense & my pea brain just isn't firing on all 4 cylinders lately.

Seems like if you use the original cam, head & caps all fits like a well worn glove. If you put a used cam in you have different wear on the cam vs nuts & head.

If you put the original cap on then you have wear grooves on the cap and head that match but the cam doesn't fit that set of grooves. I wonder if that will cause lubrication difficulties till all wear in to their new settings.

But if you put the caps on that came with the replacement cam you have half the wear grooves that exactly match the cam so only the head half has to mate properly and maybe you get better lubrication to the journals that way?

This is a question as I really have no idea which works best when putting in a used cam in a used head. Using plastigauge all the caps are WNL & there's no issue with too tight or too loose a fit with both the original caps and the ones that came with the cams.

[natemoen]

I've been looking but darned if I can find the order listed. O'course the manual has real omissions like not mentioning the ring bevels facing up on #2 ring in the assembly section, & that detail was only alluded to in a drawing under "Engine maintenance" in section 7 & no mention of it was made.

So... It's entirely possible I've missed where they hid the torque sequence detail.

I will double check in a few minutes for you on the order.

[natemoen]

Page 78 in the clymer says 3-4-2-5-1.

[KA1J]

Page 78 in the clymer says 3-4-2-5-1.

Beautiful! I don't have the Clymer though I have two different Yama service manuals ( one for the XS11 & the other for the XJ11). I'll use 3-4-2-5-1

After looking carefully at the surfaces on the caps, it looks like the original caps are scored a bit more than the ones that came with the lower mileage used cams and both sets of caps mic out the same with vernier calipers as well. Since both sets of caps spec out fine with plastiguage and the newer caps well, look newer & spec the same as original, I'm going to use the ones that came with the cams.

Thanks for looking the torque order up, I appreciate it.

[cywelchjr]

I'm trying to understand what makes the most sense & my pea brain just isn't firing on all 4 cylinders lately.

Seems like if you use the original cam, head & caps all fits like a well worn glove. If you put a used cam in you have different wear on the cam vs nuts & head.

If you put the original cap on then you have wear grooves on the cap and head that match but the cam doesn't fit that set of grooves. I wonder if that will cause lubrication difficulties till all wear in to their new settings.

But if you put the caps on that came with the replacement cam you have half the wear grooves that exactly match the cam so only the head half has to mate properly and maybe you get better lubrication to the journals that way?

This is a question as I really have no idea which works best when putting in a used cam in a used head. Using plastigauge all the caps are WNL & there's no issue with too tight or too loose a fit with both the original caps and the ones that came with the cams.

The issue you are may have with using the caps from another head (not will but may) is that they are machined to the head, and they may not end up matching the same. They are even supposed to stay in the same position in the head. It would be FAR worse IMHO to use caps from another head with the cam from that head in your head than to use your caps with the cams from another head. It's not wear grooves that matter, it's machining tolerances since the machined surface IS your bearing.

[KA1J]

Cy,

What you said makes sense. Perhaps they join the caps to the head and then use a precision drill bit to make the holes precicely to match & a different head would perhaps sit a little differently when drilled and mating the cap from one would not meet well with the other head. Something like that...

I did compare the two sets of caps together using plastigauge to determine gap tolerance. Some of the plastigauge tolerances were close to the outer limits of tolerance (more gap) when measured with the original caps, and they were more centered in tolerance with the "replacement" caps. It does seem like the better tolerances would be mo' betta' but Your explanation again, makes sense.

[crazy steve]

I don't know if there's a 'right' answer here....

You've got trade-offs whichever way you go. Cy is very likely correct, the caps were probably machined with the head originally, but if you get a better clearance number with the new caps, I would tend to favor those. The 'new' caps will be the part of the bearing surface that takes the majority of the thrust loads and are worn to the cams, so that's a plus.

The interesting part is Yamaha listed the cam caps as separately-purchasable parts for the XS heads (leading you to think that they're interchangable), but didn't on the XJ head (only available with the complete head). This will be a judgement call.....

[KA1J]

Progress!

Dots lined up with TDC!

Now that I have a different cam in there I need to see what the shim values are & which new values are needed.

May actually hear it running before the snow flies...

[crazy steve]

Good deal!