Gaskets and camshaft questions.

[madmax]

 I have the XS Performance "big fin" 750cc kit & camshaft fitted and intend pulling my motor this winter to sort a few cosmetic issues, while it's out there are a couple of things I'd like to address:-

 1. When I installed the big-bore kit, I used the composite head & base gaskets supplied, I believe these to be considerably thicker than standard Yamaha gaskets so I'm not getting full advantage of the compression increase afforded by the 80mm pistons. Ideally I'd like to replace these gaskets with copper ones but I don't know what thickness to order (I'll have to buy them from the USA, none available here in the UK or Europe so I'd like to get this right 1st time!). Can anyone advise what thickness standard Yamaha gaskets are (0.043"?) or alternatively advise what thickness is safe so I won't have any valve - piston interface problems?  (yes I'll clay the top end to measure clearance).    

 2. The XS performance camshaft - I'm not entirely happy as to where in the rev range it's moved the power band so I'm considering putting the Yamaha cam back in, any experience or comments/advice on this? I don't have the spare funds for a new/regrind as this years budget is going on a PMA.

  Thanks guys

   Max

[grizld1]

Hi Max,
You may not like this response, but when it comes to building a motor with performance mods, you need to take your own measurements if you want to get the performance you've paid for and avoid damage. Right, the OE gasket runs about .043" after compression. I don't know the thickness of the Mike's XS big bore gaskets. You may want to cc out your motor and find out what your present static CR really is before you play with the deck height. If you need a procedure for this, just ask and I'll post one.

Re. the XS Performance cam: the grind is a clone of the Megacycle 250-00 and the design is very poor (I'm restraining my language here). Unless you want to mount the sprocket on the slots and trust two 7 mm. screws to hold it (which I wouldn't do on a bet--there's a reason why everyone else uses a 3-point mount), the only way to degree the thing in is by tweaking deck height. That camshaft will make your motor shake like a dog passing peach pits anyway. I just finished removing one from my motor and reinstalled my old Shell #1. Things are much better now.

Remember--changing gasket thickness changes deck height, and changing deck height changes cam timing. I don't know if height on the XS Performance jugs is the same as OE or not, but if I were you I wouldn't take it for granted.

650 Central sells copper gaskets in a range of thicknesses, and you could play with several combinations to get where you want to be. Don't let any smart guy tell you that copper gaskets will seep. If you anneal the gaskets properly and use an appropriate sealant like HK Copper Kote, it ain't gonna happen. My own head gasket uses two layers of copper sealed together.

[madmax]

 Thanks Griz, wise words as usual.

 I'll take you up on the offer of the procedure for cc'ing the motor and when I do get to take things apart will take some accurate measurements of deck height on old V's new barrels and also try and get some meaningful measurements of old V's new pistons (Gudgeon pin to crown). Don't suppose you have a thickness for OEM base gaskets do you? I can't imagine they compress very much?

  Thanks again.

   Max

[richard]

if it's any help I have two unused head gaskets here they both say 1.5mm, one measures 1.73mm and the other is 1.66mm. The thickness varies a little depending on where you measure them. These are not copper gaskets they are just standard retail gaskets.

Also being that I save everything I do have a used stock gasket that came off my 1982. I measured it and it was .51mm thick. It was probably re-torqued a number of times through the years by the previous owner. I also have an un-opened Emgo gasket set which has a D&K gaskets in it. I'm willing to measure that head gasket too for you if it will help. I just used a digital caliper to measure them.

I didn't use any kind of sealer on my head gaskets on either of the two bikes I ride the most, In retrospect I wish I had. They are not a problem, but anything to make them seal better would be an improvement. They kind of seep or mist over time. not enough to make visible oil drip, but enough to collect dust about center of the head below the spark plug on either side. We have no shortage of dust in the air here in the summer time.

[grizld1]

Best to measure head gasket thickness at the fire ring, Richard. Those 1.5 mm.gaskets are probably from Athena, and I have a couple of them in the stash that I'll never use; the last thing the old twin needs is advanced valve timing, though I guess if somebody wants to throw a motor together with a stretched out cam chain and still get the timing to dial in right that would be a cheap fix--for awhile, anyway! Vesrah head gaskets are made to OE specs.

OE base gasket thickness is .020"/0.5 mm. Right, Max, you won't see compression of the material there.

[grizld1]

Max, you want to cc the motor out before you take it apart. You can get into all sorts of complications with fancy math, but this procedure will get you as close as you need to be--this ain't rocket science.

1. Block up the motor on the bench so that one spark plug hole is vertical, so that all air will be purged from the combustion chamber when you fill it with oil. Set up a degree wheel and pointer on the crank.
2. Locate TDC and zero the degree wheel.
3. Use a cap with a spout from a gear lube bottle or similar to create a small funnel that will rest flat on the plug hole. Cut the spout so that it extends to the bottom of the threads--no more and no less.
4. You'll need two measuring tools--a small graduated cylinder and a small dosage vial from the drug store. Note that the liquid you're measuring forms a curved lens shape. Measurements are taken at the bottom of the curve.
5. Make sure that valves are closed on the cylinder you're working with.
6. Using your usual motor oil, pour 40 cc.'s into the plug hole with the graduated cylinder; then carefully add oil with the small dosage vial until it reaches the bottom of the funnel. Gently rock the motor back and forth a very little bit to
release any trapped air, and add oil to reach the funnel again if needed.
7. Record the volume of oil added; this is the combustion chamber volume.
8. Rotate the crank to BDC (180* on the degree wheel), turning CCW as seen from the left, CW as seen from the right. Add oil as before, measuring carefully and recording the number. This is the swept volume of the cylinder.
9. Add swept volume to combustion chamber volume. Divide combustion chamber volume by the total. This is the static compression ratio. CR=combustion chamber volume /(combustion chamber volume+swept volume of cylinder).

[richard]

Measured at the ring, that's the only way I know to measure them, the two spare Gaskets are marked 'Motor Gasket MOII5' and they came from Mikes XS. The other one came EMGO and is marked D&K still in the cardboard and shrink-wrap. The used gasket is OEM off the 82, The gaskets On the 71 are NOS which was a little over 1mm before I used it. The 71 has 9000 miles since rebuild, no problems so far.

I'm riding the 1980 more often now that I have all the bugs worked out. The 71 has more power, but I really like the 1980 because the electric start is easy on my old bones, no effort.

[grizld1]

The thick stuff from Mike's XS is no surprise, but I'm puzzled by the .051" gasket from your 82, Richard. I don't question that you got that measurement, but it's not typical. From 1974 through end of production, Yamaha shows the same part number for top end gasket sets. I've broken down more than a dozen 447 motors, and I've never seen an OE gasket that thick.

[richard]

OK I re-measured it and I was wrong. Probably pushed the button on the caliper one too many times.

re-measuring it and correct was 1.16mm which sounds one heck of a lot more realistic. and in inches it's .050 thousandths at the cylinder surface ring which is magnetic on all of them so it's probably tin or something like it.

[grizld1]

Thanks, Richard; one of these days I'll learn how to read! 0.51 mm. is a very odd measurement. I doubt that retorquing would crush an OE head gasket to less than half its original thickness, for several reasons. First, I've never seen significant variation from original thickness in the many old XS650 gaskets I've examined; studs would be breaking or spinning before they took the pressure needed to compress the gasket to that extent. Second, crushing to less than half of the original thickness would cause obvious distortion. Finally, the only head gaskets that thin that I've seen on any motorcycle have been copper. You have something very unusual there!

[richard]

No your right to be suspicious Grizld1. My measurements on the squashed gasket were wrong. It seems very logical that you can't squish 1.5mm down to .5mm As it turns out I inadvertently pushed the button on the caliper one too many times. After measuring it again turns out it is 1.16mm or .050 thousandths. I tried to find some markings on the gasket and couldn't find any. It just appears to be brown and magnetic on the cylinder ring gasket surface. I too favor copper gaskets if I can get them. I started with copper on the dirt bikes and I have never had any problems with copper on any others. I think it is superior. In the old days before we had money we used to just anneal copper gaskets with a torch and get at least one more reuse out of them, thinner didn't hurt either. When it comes to gaskets I just look at and measure them, and if it looks inferior I just don't use it. Which is why I have a collection of gaskets to look at, that somehow didn't do it for me at the time.

Going back and looking at this stuff sure make me glad I followed you guys advice on the 71 and went back with NOS every chance I got. Even half a millimeter of deck can make a big difference on compression, and timing too. That may be why the 71 just seems to run better than my other XS650s which should be more or less the same aside from suspension tweaks.

[grizld1]

Richard, if you like copper gaskets, Lani Visconti at Copper Gaskets Unlimited does a great job for a very reasonable price: www.coppergaskets.us, phone [phone].

[richard]

Wow that's really cool! I do use copper gaskets and I use them for some of my R&D on oil cooling so that will come in very handy. Thanks I'll check them out.

[madmax]

Nov 22, 2014 10:51:00 GMT -5 grizld1 said:

Max, you want to cc the motor out before you take it apart. You can get into all sorts of complications with fancy math, but this procedure will get you as close as you need to be--this ain't rocket science.

1. Block up the motor on the bench so that one spark plug hole is vertical, so that all air will be purged from the combustion chamber when you fill it with oil. Set up a degree wheel and pointer on the crank.
2. Locate TDC and zero the degree wheel.
3. Use a cap with a spout from a gear lube bottle or similar to create a small funnel that will rest flat on the plug hole. Cut the spout so that it extends to the bottom of the threads--no more and no less.
4. You'll need two measuring tools--a small graduated cylinder and a small dosage vial from the drug store. Note that the liquid you're measuring forms a curved lens shape. Measurements are taken at the bottom of the curve.
5. Make sure that valves are closed on the cylinder you're working with.
6. Using your usual motor oil, pour 40 cc.'s into the plug hole with the graduated cylinder; then carefully add oil with the small dosage vial until it reaches the bottom of the funnel. Gently rock the motor back and forth a very little bit to
release any trapped air, and add oil to reach the funnel again if needed.
7. Record the volume of oil added; this is the combustion chamber volume.
8. Rotate the crank to BDC (180* on the degree wheel), turning CCW as seen from the left, CW as seen from the right. Add oil as before, measuring carefully and recording the number. This is the swept volume of the cylinder.
9. Add swept volume to combustion chamber volume. Divide combustion chamber volume by the total. This is the static compression ratio. CR=combustion chamber volume /(combustion chamber volume+swept volume of cylinder).

Thanks for that Griz, I'll give it a go and report back with results later (don't hold your breath), the other thing I want to do is measure the height of both sets of barrels from base gasket to head gasket faces, use this to determine base gasket thickness so that the deck height with the 750 barrels is the same as would be with original 650 barrels and therefore calculate head gasket thickness to maintain original Yamaha valve timing with the stock cam, does this make sense?

  Cheers

     Max             

[grizld1]

Does that make sense, Max? Uh, not really. Your original concern was to avoid sacrificing compression. You can't address that concern if you're worried about conserving OE deck height. Second, conserving OE deck height isn't a 100% guarantee that valve timing will be right. You need to assemble your motor without top end sealants so that you can take it apart again with minimum fuss, find your numbers on static CR and valve timing with the gaskets you have, and make your decisions from there.