701 -can't figure out what went wrong

[SJ/XPBri]

Some of you guys might remember my "cheap ass 701 build" from the other board. Here's what it is"
61X bored once over
Single 44
Reed Stuffers
B-Pipe
All of the ports have been cleaned up, and matched to the sleeves
R&D Girdeled head with 35cc domes.

Here comes my problem- the motor has 210 PSI in both cylinders (It's a new snap-on gauge, so I know the reading is on)
the squish is at .072- which seems HUGE.
So my question is, will it run like a POS, or should it be OK?
Also if anyone has ideas on initial jetting specs, please let me know.
Thanks,
Brian

 

[Matt_E]

I don't believe you really have 210 psi with that squish band, at that bore, with those domes. 190, tops.

The gauge is off. Yeah, it's a new snap-on - but still, it's off.
It's possible the cylinder is decked, but that should be indicated by a smaller squish.

 

[SJ/XPBri]

Matt, I know it seems crazy, but I'm 100% that the gauge is on the money. I hate to bring up sit downs, but I verified the reading on the XPL, and tested it against the shop compressor. I've gone through half a roll of solder in disbelief of the squish reading. I bought this head from someone on the boards, is it possible that the domes could be for a different bore?
Thanks,
Bri

 

[Matt_E]

They're either for a 81mm bore or for an 84mm bore.

The 81mm dome should measure 83-83.5 mm wide.
You may want to measure the diameter of the domes (inside, combustion chamber, plus squish band.

If it is for an 84mm bore (should measure 86 mm), then yes, you might get a higher reading.
Still, I am not so convinced. Make sure those domes really are 35cc domes.
Take them out, measure the diameter.
Put a spark plug in, take a syringe or something like that and measure out 35 cc of water and put it in there. Verify they are really 35cc domes.

Also, I recall reading something by Harry Klemm recently where he was describing having two Snap on gauges in his shop, that would read 30 psi apart.
The factory told him they are both correct. :bigeyes:

They told him he could send them back in if he wanted to.

 

[njfl]

Bri,

I think you bought that R&D head from me and if you are using the same domes, they are definitely for a 701.

Joe

 

[SJ/XPBri]

OK- 81mm, pulled the head and checked the cc's which is going to be hard to believe, 33 cc's. Here's a pic.
Bri
EDIT: Joe, just saw your post, thanks for the info

 

[Matt_E]

There's your answer then. 33 cc domes should yield about that compression. Maybe a bit high, but still better than 210 @ 35cc.

Do something about that squish...that's horrible.

 

[SJ/XPBri]

There's your answer then. 33 cc domes should yield about that compression. Maybe a bit high, but still better than 210 @ 35cc.

Do something about that squish...that's horrible.

That's the problem Matt- I can't figure out why the squish is so high. I'm running the smallest base gasket possible, should I run no base gasket, and just use sealer?
Thanks,
Bri

 

[njfl]

From ADA's website, 33cc would be 200psi. I don't see any reason why the R&D setup would be much different. Like I mentioned, I was running these on pump gas (93) with no problem.

 

[njfl]

Bri,

What base gasket thickness are you currently using? I have an extra 0.010" or 0.015" (I don't have a gauge with me, but it's thinner than a 0.020" spacer plate that I have) that you can either pick up in Belmar tomorrow (if you need it yesterday) or I could mail Monday for $10.00, shipped. It's Gasket Solutions PF-4N material.

Joe

 

[SJ/XPBri]

Bri,

What base gasket thickness are you currently using? I have an extra 0.010" or 0.015" (I don't have a gauge with me, but it's thinner than a 0.020" spacer plate that I have) that you can either pick up in Belmar tomorrow (if you need it yesterday) or I could mail Monday for $10.00, shipped. It's Gasket Solutions PF-4N material.

Joe

Joe,
The gasket I'm currently using is .013", Thanks very much for the offer, if I need that .010 I'll send you a PM tomorow.
Thanks Again,
Bri

 

[Matt_E]

Running no base gasket is not an option. If you're sure you're running the thinnest base gasket possible, you could get the cylinder decked - that'd be about the only way to fix that squish.
However, that will also increase your compression.

NJFL: If he's on a fresh bore & hone, he may very well be above the compression you had. Also, he's went up in bore size, so the compression will be higher.
Was your cylinder ported?

 

[SJ/XPBri]

Was your cylinder ported?

Yes, but not very much, the ports were all cleaned up, but nothing drastic. BTW, how ****ty should it run with the squish that large, and the compression so high?
Bri

 

[Matt_E]

To be honest, I do not know. You may want to give it a try.

 

[SJ/XPBri]

This thing has been keeping me awake at nights :bigeyes:
Here's what I did, decided to pull the head and measure the actual distances at the cyinder wall. Well the reading adds up to .040" (.006" from the edge of the piston to the deck, and .034" at the same point in the head) I think that the solder is getting pushed away buy the crest in the piston.
So, my question: Is this an acceptable way to calculate the squish?
BTW- The head does fit flush with the cylinder.
Thanks,
Bri

 

[Matt_E]

If that includes head gasket thickness, you should be good.

 

[Mile9c1]

I've been told that with more squish you can rum more compression with less octane. I think you'll be fine, watch the WOT runs though if you're on pump gas.

 

[SJ/XPBri]

If that includes head gasket thickness, you should be good.

Yup It's an o-ring head. Sweet, I'll sleep well tonight, thanks Matt.
Bri

 

[Matt_E]

I've been told that with more squish you can rum more compression with less octane. I think you'll be fine, watch the WOT runs though if you're on pump gas.

I do wonder, however, what would give you more power-benefit...tighter squish at lower compression, or less squish at higher compression.

 

[egbrig]

When you measure the squish where are you putting the solder, it matters, there is a proper way to do it or your going to get messed up measurements. PSI compression readings is not what matters. Its the mechanical compression ratio that counts. Too many factors come into play when talking about psi readings, psi readings are indicate the condition of seal between the rings and the cylinder wall. Also did oil get into your guage? 40 thous squish is cutting it close with a stock crank and rods.