Where to start - putting it back on the road

Got a customizing or restoration project? Post your progress pictures and updates here

Moderator: rztom

Message
Author
steveho
Posts: 229
Joined: Thu Aug 20, 2015 4:01 pm
Location: Southampton, England

Re: Where to start - putting it back on the road

#181 Post by steveho » Tue Dec 18, 2018 8:14 am

FYI, genuine head and base gaskets are still available from Yamaha.
In the UK Fowlers have a good web-site to check availability and pricing. Handy, so you don't have to rely on them popping up on eBay.
Around £160 for all 6 gaskets is about right.

PaulGreen
- - - - -
- - - - -
Posts: 289
Joined: Wed Aug 22, 2007 6:58 am
Location: Grimsby, NE Lincs, England.

Re: Where to start - putting it back on the road

#182 Post by PaulGreen » Thu Dec 20, 2018 1:24 pm

Due to the poor compression I've got the top end off again, there's nothing obviously amiss, I'll dig out the specs and have a proper look at it.

Re the top cylinders not firing, the pick up coil checks out ok electrically, I'm not sure how I would check the gap though. One thing I did notice was one half of the magneto is mildly corroded/tarnished and of the two raised sections was a little tarnished looking. It's also very slightly chamfered along it's face. IE it's 2.2 mm high on one edge down to 1.8 mm on the other. Not sure how sensitive the whole magneto/coil/gap set up is?

Cheers,
Paul.

silverstrom
- - - - -
- - - - -
Posts: 3238
Joined: Sat Feb 04, 2012 7:36 am

Re: Where to start - putting it back on the road

#183 Post by silverstrom » Thu Dec 20, 2018 3:36 pm

My information says the pick-up gap should be 0.7 mm. More than that and you can run into weak spark issues. Some have closed the gap to 0.5 mm to get the best spark possible. The gap between the pick-up and the 2 small raised parts on the flywheel.

The raised sections on the flywheel should be clean, but a little tarnish should not cause huge problems. If they are no longer magnetic you have a bigger problem.

Hopefully someone with better knowledge of this will comment to help you further.

PaulGreen
- - - - -
- - - - -
Posts: 289
Joined: Wed Aug 22, 2007 6:58 am
Location: Grimsby, NE Lincs, England.

Re: Where to start - putting it back on the road

#184 Post by PaulGreen » Thu Dec 20, 2018 4:13 pm

silverstrom wrote: Sun Dec 16, 2018 5:51 pm Unless you have made the same monumental mistake in all 4 cylinders
I've been checking and measuring piston rings today, end gaps are all well within tolerance.

However, I'm wondering if I had them fitted correctly?
I have the expansion ring in the bottom groove with the narrower gauge (laterally) ring, with the thicker ring in the top groove.

I can't find any information about which way round they should go but I noticed that all the stock photos of piston kits I've seen show the expansion ring with the thicker of the two rings.
Is this where I've gone wrong? That certainly falls into the category of "same monumental mistake on all 4 cylinders" and would explain the consistency with poor readings.

Thanks
Paul.

silverstrom
- - - - -
- - - - -
Posts: 3238
Joined: Sat Feb 04, 2012 7:36 am

Re: Where to start - putting it back on the road

#185 Post by silverstrom » Thu Dec 20, 2018 8:37 pm

Are you using Yamaha pistons and the Yamaha manual?

For Yamaha pistons the lower ring is a plain ring and is slightly narrower than the top ring. The bottom ring is narrower because it has the expander behind it.

The top ring is a Keystone ring (bevelled) and is slightly wider than the lower ring. It has to be installed the correct way. You don't want to install it upside down. Any writing on the ring should be the top surface. Typically it's difficult to put them in upside down because of the way they fit the ring pegs, so you should be good there.

That is typical with most piston manufacturers, at least that I have worked with.

Check your piston to bore clearance. If the bore is too big for the pistons you'll have problems. Also, if your bores are oval you'll have problems.

PaulGreen
- - - - -
- - - - -
Posts: 289
Joined: Wed Aug 22, 2007 6:58 am
Location: Grimsby, NE Lincs, England.

Re: Where to start - putting it back on the road

#186 Post by PaulGreen » Sat Dec 22, 2018 7:27 pm

Yes, I'm using the workshop manual.
In the engine build section there's no reference to an expansion ring, or any differences between the rings. But I did find a better description in the appendix. So I'm confident that the rings were installed correctly. They've never been upside down!
I was kind of hoping that it was a ring issue, a simple fix that would explain why all 4 cylinders are down by the same amount.
All ring end gaps and side clearance are well within the tolerance limits.

Due to not having the correct equipment I've never checked the bores themselves other than visually and feeling for any lips at the top of the stroke. Obviously I'm hoping that's all clear but I'm doubtful that the drastic loss of compression can be just down to pattern head gaskets

I'm now waiting for a bore gauge to arrive to make sure that the bore/piston fit is within spec.

Thanks,
Paul.

PaulGreen
- - - - -
- - - - -
Posts: 289
Joined: Wed Aug 22, 2007 6:58 am
Location: Grimsby, NE Lincs, England.

Re: Where to start - putting it back on the road

#187 Post by PaulGreen » Wed Jan 30, 2019 7:02 pm

Well, today I got back in the garage and measured everything on the top end. Then I measured it again.
Everything is well within tolerance.
So I've made a start putting it back together. Again.

I read somewhere that crankcase seals can affect compression. I'm struggling to see how that might be so, any thoughts appreciated.

Cheers,
Paul.

silverstrom
- - - - -
- - - - -
Posts: 3238
Joined: Sat Feb 04, 2012 7:36 am

Re: Where to start - putting it back on the road

#188 Post by silverstrom » Wed Jan 30, 2019 9:10 pm

PaulGreen wrote: Wed Jan 30, 2019 7:02 pm I read somewhere that crankcase seals can affect compression. I'm struggling to see how that might be so, any thoughts appreciated.

Cheers,
Paul.
That would be impossible. Compression occurs when the piston rises high enough to close the intake and exhaust ports. So....you are only measuring compression at the top of the cylinder, above all intake, transfer and exhaust ports.

PaulGreen
- - - - -
- - - - -
Posts: 289
Joined: Wed Aug 22, 2007 6:58 am
Location: Grimsby, NE Lincs, England.

Re: Where to start - putting it back on the road

#189 Post by PaulGreen » Thu Jan 31, 2019 4:41 am

That was my understanding too, thanks for clarifying.

User avatar
TwoStrokeNut
Posts: 585
Joined: Tue Nov 20, 2012 5:12 pm
Location: Florida,USA

Re: Where to start - putting it back on the road

#190 Post by TwoStrokeNut » Thu Jan 31, 2019 9:31 am

PaulGreen wrote: Wed Jan 30, 2019 7:02 pm /snip/
I read somewhere that crankcase seals can affect compression. I'm struggling to see how that might be so, any thoughts appreciated.

Cheers,
Paul.
Let me start out by saying I'm still learning about my RZ500 and RZ's in general, so please forgive my ignorance.

I think its plausible that a massive crankshaft seal leak (or any crankcase leak) in a 2-stroke could in some way affect overall compression readings at the spark plugs. After the air/fuel charge is inducted into the crankcase (whether through the crankcase reeds or cylinder barrel reeds), it is slightly compressed with the dropping piston and forced up through the transfer ports to the bore above the piston. Main compression starts when the exhaust port is closed with the rising piston. If there's another path for the charge to escape from the crankcase rather then being forced up the transfer ports, its feasible that 100% of the charge may not make it to where it was intended (in the combustion chamber). Less charge above the piston at the start of compression could mean slightly lower pressure and could result in a lower overall compression value when the piston reaches TDC. Of course, there is still that timed exhaust back-pressure pulse that also tries to keep the fuel/air charge from escaping (and boosts initial compression pressure, I would think) and that must come into play as well.

There are a lot of if's, could's, and may's in that statement, so I could be way off base.
Project bike links: NS400R - TRIPLE THREAT // RZ500 - MOSQUITO CONTROL BIKE // RZ350 - REVIVAL
'72 H1-500/'75 H1-500/'85 RZ350/'85 NS400R/'01 DR650/'07 FJR1300/'18 Tiger 1200

PaulGreen
- - - - -
- - - - -
Posts: 289
Joined: Wed Aug 22, 2007 6:58 am
Location: Grimsby, NE Lincs, England.

Re: Where to start - putting it back on the road

#191 Post by PaulGreen » Thu Jan 31, 2019 2:15 pm

Ready to go back in.
Again.

Image

Image

Image
Last edited by PaulGreen on Thu Jan 31, 2019 3:17 pm, edited 4 times in total.

PaulGreen
- - - - -
- - - - -
Posts: 289
Joined: Wed Aug 22, 2007 6:58 am
Location: Grimsby, NE Lincs, England.

Re: Where to start - putting it back on the road

#192 Post by PaulGreen » Thu Jan 31, 2019 6:03 pm

Image

silverstrom
- - - - -
- - - - -
Posts: 3238
Joined: Sat Feb 04, 2012 7:36 am

Re: Where to start - putting it back on the road

#193 Post by silverstrom » Thu Jan 31, 2019 7:17 pm

Some advice, if I may. Before installing the engine do a compression test. It can be challenging without having the engine mounted in the frame, but now is the time to do it. Use a different compression tester. New ones are not expensive. Make sure the compression tester threaded fitting at the spark plug hole is tight and has a good o-ring sealing it.

Do a leak-down test as well. It is far easier to do on the bench.

Did you measure the bores to make sure they are not oval? It's difficult for round rings to seal an oval hole.

PaulGreen
- - - - -
- - - - -
Posts: 289
Joined: Wed Aug 22, 2007 6:58 am
Location: Grimsby, NE Lincs, England.

Re: Where to start - putting it back on the road

#194 Post by PaulGreen » Thu Jan 31, 2019 7:41 pm

Some advice, if I may.
You may, I'll always take advice......

I was wondering about a comp test on the bench but figured it was going to be too difficult to get the motor sat sturdily enough.
Maybe my drill on the flywheel nut will have enough power to turn the motor with the plugs removed?


I measured bore for roundness and taper and pistons as per the manual, everything was well within spec.

Looking into a leak down test now...

thanks,
Paul.

silverstrom
- - - - -
- - - - -
Posts: 3238
Joined: Sat Feb 04, 2012 7:36 am

Re: Where to start - putting it back on the road

#195 Post by silverstrom » Thu Jan 31, 2019 8:07 pm

If you do a search for "leakdown test" on this forum you'll find plenty of information.

I always recommend doing the test on each cylinder. My experience shows that a small air leak on the right side will not always show up when testing from the left cylinder. By testing each cylinder separately you'll be sure to pick up even the smallest of leaks. Air pressure from the left side will pass through the labyrinth seal and pressurize the right side of the crank-well, but if the right side seal leak is small it will not always show up as expected. This I know from my own test results here. I've tested from the left side and had the test be successful, but when I tested from the right side it failed. Now I test each cylinder and I am assured that the results are accurate.

Not long ago I was testing an RZ350 engine and from the left side it was a successful test. When I tested from the right side it only got to 3.5 PSI and then dropped to 0 PSI. I tried multiple times and got the same result. The right side crank seal was beginning to leak but hadn't completely failed yet. Had I taken the result from the left side and not tested from the right side I would have had the engine running with a crank seal leak and would have only discovered it when it started consuming gearbox oil.

Obviously if you have a massive seal failure you'll know instantly because you'll get 0 PSI from the left or right. Those failures are easy to find. Finding smaller leaks requires a different approach. It's worth the extra time to test each cylinder separately. That is the only way to be absolutely certain that all is well.

By the way...great looking engine. You do good work :smt023

Post Reply