Rebuilt Super Rat Compression

[viclioce]

I have two of these bikes! Both have rebuilt motors. New pistons, new rings, new bore, new bottom end kit, with new bearings & seals Neither will start. These are the only bikes I’ve had this issue with. Just the Super Rats.

The first is giving me only 85 lbs/sq. in compression. The second is giving me 115 lbs/sq.in compression, and this one was bored by Hodaka Dave.

What should I be checking here? These are the only Hodakas to ever give me this problem. Victor

[taber hodaka]

I do not believe that you will get high compression with a dykes ring. I set mine up tight but you better use the best of oil, if you do. I am looking to see what others say? ---Clarence

[Bullfrog]

Note that compression happens between the top of the exhaust port and top dead center. So the question is, what items are involved with being air-tight between the exhaust port and the spark plug? Are ALL of those items doing their job properly?

Compression tester seal at spark plug hole and no tester leaks? Correct head? Head gasket sealing properly? No cracks in head or cylinder or piston? (Sounds silly to say that - but SOMETHING is wrong . . . ). Broken ring?

Ed

[MTrat]

Ace head over Rat piston?

[viclioce]

Correct head, new head gasket, new piston & ring on both units. One is set up for reed valve, with the 115 psi. The one with 85 psi no reed valve. Victor

[Dale]

Troubleshoot one bike at a time.
Have you performed an air leak down test?
What does or doesn't it do when you try to start it? Choke on or off? If you are way rich, it won't fire with choke on.
Does it have spark?
Triple check the point gap.
Is it getting fuel? Will it pop with a little fuel introduced?


My .02 cents

[Dale]

Regarding your compression readings...
Do the pistons utilize single dykes rings?
If so, I think your bike with 115psi is fine. The one that measures 85 is an issue. Did the dykes ring get installed upside down? The widest part of the ring has to be down. This forces the ring outward under compression. What clearance was this piston set up for? And, what was the ring gap?

[matt glascock]

Head nuts properly torqued? Spray some soap solution over the head, kick it over slowly, and observe. Simple top-end leak-down test. Check all the sites the Captain mentioned including any connections built into your compression gauge.

[Dale]

The silence is deafening...
Have you made any progress?

[viclioce]

Both motors have single dykes rings, which are properly installed. I didn’t measure the ring gaps when I put the top end together. Usually hasn’t been an issue. Hodaka Dave does the fitnent when I had the bore & porting work done on the 93B. The 93A got a new piston & ring but measured within the tolerances specs in Terry’s library.

These Super Rats have really pissed me off. They are the only Hodakas which have given me this much issue and difficulty. I’ve been fighting with tge 93B since January and the 93A since March. I get frustrated & just walk away from them & go on to other projects.

I purchased a TDC gauge so I can set the pistons at exactly 2.9mm BTDC. The 93B with the 115 compression was started by the local 2 stroke expert at the local Suzuki/Yamaha/Kawasaki dealer. This was before we determined the crank was warped and I had to take the motor apart Snd put in a replacement crank. I’m hoping with this tool, I can set it accurately enough that the 93B will start again. The 93A has not yet been started. I’ve tried, but it’s yet to fire. This is what lead me to checking the compression because it was about the only thing left I haven’t done.

And of course, it’s all because I have buyers waiting for these 2 bikes. I did the Ace 90 from start to finish in 6 weeks. Started on the first try. Just don’t understand why the Rats are being so damned difficult. Wish there was one of you close to me who could come by & check to see what I’m missing… Victor

[Dale]

Victor,
Okay, that brings us all up to date on these 2 bikes. I can't keep your projects straight and don't know how you do!

I'll first say that the issues have zero to do with them being Super Rats. There has been and continues to be at least one issue with each bike that is a show stopper. To troubleshoot and resolve them is the challenge.

I feel like once you get a good working crank installed in the 93B that you will have a runner. I say this knowing that you had experienced carburetor issues too and hope that you have them resolved.

As for the 93A, I have many questions regarding the new piston and ring without a re-bore on the cylinder. Unless you had a very experienced 2-stroke mechanic perform the measurements on the bore, then confirmed the piston clearance and finally set up the ring gap, then I would not have any confidence in it. Also, was the bore honed prior to installing the new piston and ring? If the answer is "no" to any of this then that is most likely the compression issue.

Keep after them, they will run!

[viclioce]

Dale. The crank has already been replaced on the 93B. I’m hoping the TDC gauge will end my issues with the 93B.

As far as the 93A goes, no, I didn’t hone cylinder. It wasn’t rusty like the 93B was, and as I recall, best as I can, the ring gap was pretty tight. Almost closed. I guess I could pull the motor and measure the ring gap, but that is not really what I want to do right now. I just have a hard time working on a bike that fights me. It’s just extremely frustrating…. Victor

[viclioce]

Starting is the only issue to resolve on both bikes to get them out of here. Just trying to keep from being frustrated with them. Victor

[Dale]

Okay, on the 93B I would use the TDC indicator (when it arrives) to confirm your case marks. You can use a buzz box with it to set your points but I find it just as easy to set the points to a .012 gap. Then start it up and check your firing point with a timing light. The timing light will give you a precise picture of your timing. Regardless of how you set your points, I would suggest checking it with a timing light to confirm the firing point. I doubt that your point gap is an issue with it not starting however. It would have to be way off...

On the 93A, I think that you have taken an ill-advised shortcut to a top end rebuild. The bore measurement requires precise measurement (or a very experienced 2-stroke builder). The ring gap must be checked and not just in one place within the bore. And finally, you should not, in my opinion, ever replace rings without the cylinder bore being honed.

Again, these are my opinions. Others might have different thoughts on it.

[taber hodaka]

If you do not chamfer the ports the ring can catch and brake. Timing to me is not critical 12 to 15 thousands will work. Measured ring end gap is very important to me I like it on the tight side of spec, looked good will not work. On the old cast iron dykes ring I have never honed the cylinder. The ring needs end gap, I measure it in the position it will be in when the piston is installed, it should be measured at the top of cylinder and at the bottom the stroke. And you also need some gap where the ring centers around the piston pin in the ring grove. I always grease the cylinder wall with grease to boost compression a little bit for initial starting. No push back, haul back or walk back. Clarence

[Dale]

If you do not chamfer the ports the ring can catch and brake. Timing to me is not critical 12 to 15 thousands will work. Measured ring end gap is very important to me I like it on the tight side of spec, looked good will not work. On the old cast iron dykes ring I have never honed the cylinder. The ring needs end gap, I measure it in the position it will be in when the piston is installed, it should be measured at the top of cylinder and at the bottom the stroke. And you also need some gap where the ring centers around the piston pin in the ring grove. I always grease the cylinder wall with grease to boost compression a little bit for initial starting. No push back, haul back or walk back. Clarence

Good info Clarence and the experience to back it up. I like it. I also set my ring gap on the tight side. I always think, what will it be after a couple of heat cycles?

[viclioce]

So you set your ring gap where? Between .006 & .008? I need to check the ring gap in the 93A. I’ll report back when I have it. Is the ring gap more critical with a single ring piston because there is no lower ring? Victor

[Dale]

So you set your ring gap where? Between .006 & .008? I need to check the ring gap in the 93A. I’ll report back when I have it. Is the ring gap more critical with a single ring piston because there is no lower ring? Victor

Don't forget the bore measurements and piston clearance.
As for the ring gap, I set mine as small as possible (like .001) I make sure that the ring ends never touch from top to bottom of of the bore surface where it will ride. This takes some effort using the piston to square the ring in the bore and to keep it square. I also use a white sheet of paper underneath and a good light.
Filing rings to get the gap you want takes some real attention to detail. And as Clarence noted, you have to account for some clearance at the pin too.
I am NOT suggesting that you should set yours up this way. I am simply stating what I do with mine.
Like oil threads, others will have differing opinions.

[matt glascock]

Great Dale. I like the white paper idea. My (brand which shall not be named) RM250 is due for a new ring.

[viclioce]

So, what kind of file is used to file the ring? Suggestions please. I don’t want to get this wrong. Victor

[taber hodaka]

Scary thoughts. please call me .- '-. Clarence

[Dale]

Here's the thing. At least this is how I see it...
The folks that do this either 1) learned by trial and error and have failed many times before they figured it out or 2) had someone teach them and then went on to fail until they got it right. I am also thinking that rings, pistons and cylinders were plentiful when their experience was being gained. There are tools and techniques involved that must be learned.

If you have one ring, one piston and one cylinder to do, I would highly recommend getting with someone that has the experience with 2-stroke motors and watch them do it. If that is not possible, then take someone up on their offer to call them. Clarence has that experience. Personally, I have just enough experience to be scary and enough to be scared.

Honestly, give Clarence a call.

[viclioce]

OK Dale! I’ll call Clarence. Victor

[viclioce]

Talked with Clarence. Have a few ideas…. Will report back. Victor

[Dale]

Talked with Clarence. Have a few ideas…. Will report back. Victor

Please do. We are pulling for you!