74 400 Cross Engine Assembly Help?

[Crashaholic]

Decided to check the manual for the length of the 2 Allen screws that come from the left side & found that I'd been using 50mm screws where it calls for 40mm.

I love it when troubleshooting a problem is solved. Its an "oh yeah the case screws" revelation. I never would have guessed that you changed out the case screws.

I think your crank clearance is okay. The notes I referred to for the 2mm clearance was for a 73 450. Since then I came across this photo of a 71 400 I opened up years ago, its looks pretty tight not to mention it had a bad crank seal.

 

[bul_racer]

Crash, I, too, love finding solutions to problems. Not so much when the answer is 'Stop doing stupid stuff.'

Thanks for this picture. I was thinking I'd just button it up now. Going to have to order a piston. Was waiting to see if I could get the bottom end together before doing that. Any recommendations for a piston source are welcome. Only one I found is Vintco.

BTW, love your moniker. Reminds me of my buddy Rick years ago when Star Wars was popular. We called him Lando Karashian

 

[Crashaholic]

Yup, "stupid stuff", been there done that. It so happens its the nature of being human.

Vintco pistons haven't been around nearly as long as other brands we're familiar with. If the bike isn't going to be raced I don't see why it wouldn't be okay, and you can't beat the price for a restoration or cow trailing bike.

 

[DeathFromAbove]

Nice find, I have used Vintco pistons and rod kits. They are fine for me but I don't go very fast and haven't started a bike since Jan because of the knees. Good Luck and keep posting so we can live vicariously!! Chris

 

[bul_racer]

Yup, "stupid stuff", been there done that. It so happens its the nature of being human.

Vintco pistons haven't been around nearly as long as other brands we're familiar with. If the bike isn't going to be raced I don't see why it wouldn't be okay, and you can't beat the price for a restoration or cow trailing bike.

There aren't many choices for pistons. Maybe find something on ebay, NOS Wiseco if you can find it, though they're not making any now & some of the ebay postings I see don't give enough information. I want to know exactly what I'm getting when I buy a piston. I sorta am planning to race it in vintage but I'm in 70+ class so even though I think I'm going fast I'm probably not stressing the engine a lot. Anyway, I can't get away very often due to wife's health issues.

 

[bul_racer]

Nice find, I have used Vintco pistons and rod kits. They are fine for me but I don't go very fast and haven't started a bike since Jan because of the knees. Good Luck and keep posting so we can live vicariously!! Chris

Chris, sorry about your knees. That really sucks! Have you considered knee replacement? The folks I know who've done that report about 98% satisfaction. I've been lucky. I did have ACL replacement surgery but my doc was the best! He was the US Ski Team doc before Steadman. 24 years and counting and no pain.

Working on getting the frame sanded & Painted. I have a tank that just has a small dent but it's in a place the repair guys said they couldn't fix. Probably try Bondo, though they don't recommend it for dents of more than 1/8 inch. This one is probably 5/8. There are a few rust holes in the bottom. I think I can solder or braze those but there's a scratch in the chrome part that I don't think I can repair without costing more than a new tank. If I decide to paint I have a friend that has a paint booth but it might still be pricey. The guy in Elizabeth, CO will be happy to fix it or sell me a refurbished tank but he wants more than the bike will be worth. Most likely I'll just try to get the bike looking reasonable, then take it out and trash it. ;-D

http://www.vintagehuskyrestorations.com/untitled1.html

I'll continue to post as the project develops but it may be slow. I'm also working on getting my 1980 Yamaha 650 street bike running after it's been sitting for the last 14 years, in addition to a Bultaco 250 Matador project. Haha! I have more projects than money.

 

[DeathFromAbove]

Yeah tanks are like gold these days I've seen him go for over a $1000 kind of crap is that. Chris

 

[bul_racer]

Piston & cylinder have 5 thousandths clearance based on feeler gauge inserted at the bottom. Micrometer reads about 4.9, though it may be more at the ports. Thinking this is OK. Maybe should be honed to get cross hatch.

Ring gap was slightly loose with .030 feeler guage. Since .028 is max spec I need a new ring.

Piston is standard and, surprisingly, Mahle. I thought Husqvarna used Kolbenschmidt. So, does anyone know how/where to get a ring for the Mahle? If not available, does anyone know if a Wiseco or other ring might work.

One other thing: The ring pin is located at the left rear of the piston, right inside the intake port. Manually moving the piston up & down does not appear to have any binding but I'm concerned that at some point the ring could snag on the port. Nothing good happens after that.

Anyone have experience with these pistons? Do they have a history of ring snags?

 

[DeathFromAbove]

^^^^ Bul-Racer said-The ring pin is located at the left rear of the piston, right inside the intake port.
That don't sound right!! I would not run like that without the piston manufacturer approving!
Is the arrow on the piston crown pointing to the exhaust port?
Pics Lots of Pics**************************************** Chris

 

[bul_racer]

Chris,

Arrow on top of the piston indicates the piston is correct with the pin in this position.

Here's a picture I found from a thread that talks about this with a pic of a similar engine. You can see from the position of the ring pin that it will be in the intake port. This is the same as mine. Clearly, it was designed to be this way. As I said, the rings do not seem to be sticking out so maybe it's OK like this.

You say you've used Vintco pistons. I'm going to make a leap and assume that they do not have similar ring pin placement.

 

[DeathFromAbove]

I think you are good and correct. I took these pics of a vintco, wiseco, and old mahle 250 pistons and they are the same. The last pic is a 73 250 cylinder and the piston location when at BDC. Looks like the ring is never uncovered! So I bet you and I are Good to go!! Chris

 

[DeathFromAbove]

Two more of the cylinder, The ring never moves down past the arrow! Chris

 

[bul_racer]

Chris, I haven't actually put the cylinder on the bottom end but it's a simple matter to simply slide it on & I can do that without the ring in place to check this out. If the ring stays out of the port then there's not going to be a problem, which will be great if, in fact, it does work that way. Maybe the designers knew what they were doing after all.

That Mahle piston in your pic don't look so good!

I'm still trying to find a replacement ring. Found 1 on ebay. Think I'll call John LeFever of Vintage Husky & see if he has any.

 

[DeathFromAbove]

yeah that mahle piston ring is not coming out!! It's scrap. I got new pistons for the 250 and sent the vintco and cylinder to power seal for boring. All ready to assemble when I get the chance. Good luck with the ring. John has a lot of stuff for these old girls. Ask him and he'll probably confirm our theory. Chris

 

[Crashaholic]

Anyone have experience with these pistons? Do they have a history of ring snags

I've never heard of a Mahle piston having problems with ring snag but then I've never heard of any piston having such issues. Its my understanding that ring snag is a lack of chamfer at the edge of the port. I had a 450 snag a ring and make a mess but cleaning up the chamfer solved it.

 

[DeathFromAbove]

Crash I think he thought the ring ends were exposed in the lower transfer port. Chris

 

[bul_racer]

Crash I think he thought the ring ends were exposed in the lower transfer port. Chris

Yes, exactly. However, with Chris' help I now see that this can't happen. Haven't talked with John yet but I did mock up the piston/cylinder and am satisfied that it is OK.

I know I need a new ring. I've been wrestling with whether I need a new piston and maybe bored out to next OS. I was getting some confusing readings from my micrometer. First, it seems every time I'd try to get a reading of the inside diameter it'd come up different. I just have a telescoping gizmo and it's hard to get readings consistent enough to have confidence in them. I thought maybe my micrometer was off but I checked it against a 1 inch standard and a 2 inch standard & both came out exact.

I was able to get a 5 thousandths feeler gauge between the piston bottom skirt and the cylinder wall, a bit tight but not overly so. When I measured with the mike at that point I came up with 4.5 thousandths, which seems like it's within acceptable range. However, when I checked closer to the ports it came to 8.5 thousandths. piston 3.2025, cylinder 3.211.

A new standard piston would be 81.42mm/3.205 inch (current piston is 2.5 thousandths smaller), so the current 3.207 at the base of the cylinder would give me 2 thousandths clearance, though there would still be 6 thousandths at the ports. Of course, I hate spending money but even more I hate to bore a cylinder unless absolutely necessary.

So, what do you think? Should I just get a new ring, replace the piston with a standard size or spring for the bore job and go up in size?

Chris, I know you like pictures but not sure showing you micrometer readings is gonna be much help.

 

[bul_racer]

BTW, standard bore size of 81.5mm equals 3.20866. Since I measured 3.207 This added to my confusion. I suppose if it's not the original cylinder a PO might have intentionally just set it up a bit tighter...

 

[DeathFromAbove]

https://onedrive.live.com/?authkey=!AEtTUP7SAuON-vc&id=2953AAE2DD855B48!246&cid=2953AAE2DD855B48
Page 23 Could be it is the original bore and is worn to almost the next size up. If you put the piston in the cylinder and can move it top to left and bottom to left, it will rattle around when running. A very little movement is ok. 5 thou, seems excessive. And the larger readings around the port won't get any smaller in the future. You can run it like it is and see what she runs like because they are very easy to pull and do the top end.
If in doubt, bore it out. Getting wonky readings is normal for me as I am not a pro. Good luck

 

[bul_racer]

https://onedrive.live.com/?authkey=!AEtTUP7SAuON-vc&id=2t953AAE2DD855B48!246&cid=2953AAE2DD855B48
Page 23 Could be it is the original bore and is worn to almost the next size up. If you put the piston in the cylinder and can move it top to left and bottom to left, it will rattle around when running. A very little movement is ok. 5 thou, seems excessive. And the larger readings around the port won't get any smaller in the future. You can run it like it is and see what she runs like because they are very easy to pull and do the top end. If in doubt, bore it out. Getting wonky readings is normal for me as I am not a pro. Good luck

Chris, this is why I love this forum! I can ask stupid questions and get serious answers!

Is your link in reference to the A-B measurement at the top of the piston?



Because I interpret this as a measurement between 2 points on the piston, not between piston and cylinder wall. I did measure this & got slightly less than 1.5mm but it's very difficult to measure that small strip of metal between the top and the ring.

I don't agree with your statement that the cylinder is worn out almost to the next size. Standard bore of 81.5mm is 3.2086 but the current measurement at the base is 3.207 & my largest measurement is 3.211 at the ports, which is far from the 3.228 of the next OS of 82mm. If I were to put in a new standard size piston of 81.42/ 3.205 that means 2 thousandths clearance at the base & 4 thousandths as the ports. This all suggests that I could get by with just a new standard size piston

I know, I should go ahead get the OS piston. I probably will...

Thanks again for your input. Much appreciated!