717 Rotary Valve Cover

[tvpierce]

I have a ‘99 GTS with a 717 single carb. I’ve done a bunch of work on it: cleaned carbs, replaced entire fuel system, replaced head gasket. Here’s my problem: it starts fine on the trailer, but when I put it in the water it won’t start. From what I’ve read, that’s a classic rotary valve clearance too large.
I’ve read that even if I get a new one from SBT, there’s no guarantee that it will bring it back to spec. Is that correct?
What’s the best option?

 

[mikidymac]

First things to do is check compression and rotary valve clearance. Are they within spec?

 

[tvpierce]

Hi Mikidymac.
I’m at the lake now. Having a family member bring the compression tester and feeler gauges when they come.

Thanks.

 

[mikidymac]

Hard starting on the water is typically low compression, fuel issue and lastly rotary clearance.

Unless there are gouges on the cases a refurbished cover can typically fix the clearance but measure it first as some have gotten back covers that are worse.

 

[tvpierce]

Quick question about checking RV clearance: I see a lot written about the solder test. Is that preferred or are feeler gauges sufficient?

 

[mikidymac]

I have always used the solder method but both should work.

 

[burtshaver2021]

Don’t forget to take the intake manifold off to remove the oring before measuring

 

[tvpierce]

Sorry for the late response. I did a compression check: 135 on the rear cylinder, 125 on the front. So not great but still serviceable, right?

Checked the rotary valve clearance via the solder method. I was at the lake, so didn't have my micrometer, but did have an inexpensive caliper so was able to get a rough estimate. It turns out I didn't need more precise measuring tools because it was so far off. See the attached pic. The top piece compressed to between .3 and .4 mm -- so close to spec. The bottom piece didn't compress at all: the .8 mm solder was still .8 mm. Is it normal to be that far off from side to side?

Is the correct course of action to replace the rotary valve cover.

 

[tvpierce]

Following up on this. Any insight is appreciated.

 

[mikidymac]

Yes, if out of spec you need to replace the cover.

Compression at 125 is very low and probably will not run much longer if at all.

 

[lavasioux]

Just a reminder that Harbor freight testers often read a good cylinder compression at about 120psi. All 4 of mine measured 120 on the hf tester, and she runs great.

 

[tvpierce]

Yes, if out of spec you need to replace the cover.

Compression at 125 is very low and probably will not run much longer if at all.

That's disheartening about the compression. Thanks for the feedback.

 

[tvpierce]

Just a reminder that Harbor freight testers often read a good cylinder compression at about 120psi. All 4 of mine measured 120 on the hf tester, and she runs great.

That’s interesting. I’d not heard that before. My tester is from HF. I do have an old tester that was my dad’s that has a rubber tip that you press and hold in the spark plug hole. I guess it’s worth testing it for a couple of reasons: 1) confirm the health of this engine 2) confirm the accuracy of my compression tester.

 

[mikidymac]

That’s interesting. I’d not heard that before. My tester is from HF. I do have an old tester that was my dad’s that has a rubber tip that you press and hold in the spark plug hole. I guess it’s worth testing it for a couple of reasons: 1) confirm the health of this engine 2) confirm the accuracy of my compression tester.

No, do not use the press in ones. Go to Autozone and they will loan you one.
Harbor Freight ones are garbage and the press in ones are not accurate either.

 

[tvpierce]

No, do not use the press in ones. Go to Autozone and they will loan you one.
Harbor Freight ones are garbage and the press in ones are not accurate either.

OK. Thanks for the heads up!