930 Valve Clearance

PJMARKOW · 07-24-2004, 04:32 PM

Well I'am at the point in my assembly where I have to decide on if I'am going to dummy asemble my top end to check the valve clearance or take a risk and seal everything up and check it. I have a 1977 930. The pistons are JE 7.5:1. The cam has been reground to 964 NA specs. Heads have not been flycut & cylinder base did not require machining. In orther words everything is standard except for the cam and new higher compression pistons. Is it woth me taking this risk or should I just bite the bullet and dummy assemble it. I'am ultra conservative and am leaning toward a dummy assembly, but compression on this motor is only going to be 7.5:1.

Cheers

Henry Schmidt · Henry Schmidt's Garage

If you didn't put valve pockets in the pistons, I would dimension the engine. You only have to do one side and it's better to be safe than bent.
PS: I like JE pistons and use them since before they were good ( mid 80s) but we have never had luck with them in turbo engines. JE has made great strides and someday they'll master the turbo pistons but to my knowledge they haven't done it yet.
Good luck

PJMARKOW · 07-24-2004, 06:33 PM

What problems did you find with the JE Turbo pistons? They seem to be used here in Australia a lot as far as I know.

Cheers

Henry Schmidt · Henry Schmidt's Garage

We have experienced excessive blowby from poor ring seating no matter which rings we used. The higher the horse power output the more the problem. We have not been able to identify the problem in design only the symptoms.
PS: 4 sale 3.3 JE pistons.(cheap) If you can figure out how to make them work, I have a very low mileage (200 or 300 miles) sitting on the self. We tried them with 2 different sets of rings. Way too much work to risk it again.

vichang4 · 07-25-2004, 08:18 AM

Quote:

Originally posted by PJMARKOW
Is it woth me taking this risk or should I just bite the bullet and dummy assemble it.

I went through the same thought process a month ago assembling my 87 3.3 (now 3.4) engine. I had also changed to RUF P & C with the same 7.5 to 1 CR. The valve clearance was more than I could measure by just tightening down the valve lash adjuster. But, I did learn a few things by going through the dry assembly, and I got some practice timing the cams. You really only need to do one P&C on one side.

Henry Schmidt · Henry Schmidt's Garage

Quote:

Originally posted by vichang4
I went through the same thought process a month ago assembling my 87 3.3 (now 3.4) engine. I had also changed to RUF P & C with the same 7.5 to 1 CR. The valve clearance was more than I could measure by just tightening down the valve lash adjuster. But, I did learn a few things by going through the dry assembly, and I got some practice timing the cams. You really only need to do one P&C on one side.

The reason that the ruf 7.5 to 1, Turbo, 98 mm, 3.4 liter pistons have excess clearance is that they are manufactured with nice sized valve pockets.
FMI
I wonder if you have noticed a slight knock / piston rattle with these pistons. The Ruf 3.4 Turbo piston has the shortest skirt I have ever seen in a production base engine. I would imagine 18000 RPM F1 engines have similar skirts but that information is secret.
As a ratio of bore size to piston skirt length not even high revving motorcycle even 14000 RPM + motorcycle piston have skirts this short.

vichang4 · 07-25-2004, 04:53 PM

Quote:

Originally posted by Henry Schmidt
I wonder if you have noticed a slight knock / piston rattle with these pistons. The Ruf 3.4 Turbo piston has the shortest skirt I have ever seen in a production base engine.

Henry,
I have not noticed any knock or rattle. I took the car to the track this past weekend and I did notice more power There is also a very noticeable increase in torque coming out of the slower turns. The track was very wet so I do not have any compareable times, but the car was faster. I also installed 22/30 torsion bars which are making a world of difference.

Fishcop · Fishcop's Garage

Paul

Definitely do the pre assembly. I know it's a PIA, but you'll sleep like a baby. I did the pre assembly thing on my 2.7 and didn't strike a problem, but I did find other issues that I was able to address without ruining gaskets and seals. You'll be surprised at how little time it actually takes as you get quite good with your tools with repetition.

PJMARKOW · 07-26-2004, 02:08 AM

Hi John,

Yeah I'd pretty much decided to do the preassemble after Henry mentioned valve pockets. The JE's have em. I did the deck height thing and the solder wasn't even touched, so I thought maybe I don't need to do the preassemble.

sand_man · 12:04 PM

Quote:

Originally posted by Henry Schmidt
We have experienced excessive blowby from poor ring seating no matter which rings we used. The higher the horse power output the more the problem. We have not been able to identify the problem in design only the symptoms.
PS: 4 sale 3.3 JE pistons.(cheap) If you can figure out how to make them work, I have a very low mileage (200 or 300 miles) sitting on the self. We tried them with 2 different sets of rings. Way too much work to risk it again.

Maybe this has been fixed, but I recently placed an order with Henry for new 98mm cylinders and new JE 98mm pistons for my 1987 930. No mention of the problem stated above was made to me. I knew that there had been some other problems with JE pistons back in the day, and it was my understanding that those issues had been worked out. Can anyone comment on this? Henry, care to take a stab? Someone put my mind at ease here. I had to put a 50% deposit on them. Yes I made it perfectly clear that these were going into a 930.

I stumbled onto this info looking for tips on the piston to valve clearance check .

Henry Schmidt · Henry Schmidt's Garage

In the past we were ordering a generic piston (shelf) that fit a general size. I.E. 98mm. The trick to having the best success with JE pistons is to have JE custom build your piston to fit your cylinders and engine dynamics.
Close tolerance is the key.
Now we order a piston with .0015"-.002" clearance and we are having excellent success.
New cylinders rather than reconditioned cylinders is also helping with our success rate.
Here is our new QSC cylinder .

DonE · 01-04-2006, 01:16 PM

Sand-man - you're OK. There are plenty of JE's in good running turbo's out there - mine included. Talk to JB Racing about JE's and you'll feel good again. I had detonation in my engine bad enough to crack 3 cylinders and punch a hole in one. All the top rings were dust. However, the JE pistons were all within spec and showed no sign of wear.

I also heard about JE pistons slapping and making noise until they warmed up. Not had any of that happen either.

As for blow-by, I have no scientific method of measurement now, but I can tell you there is very LITTLE oil film in the oil breather line when in the past (with stock Mahle stuff) I had the entire intake coated with a thick layer of oil.

I am completely satisfied with the JE pistons in my 500 rwhp stompin', 98mm piston havin', turbo.

sand_man · 01-04-2006, 02:12 PM

Thanks guys! I feel better. For the record, Henry, I didn't mean to sound so accusatory in my post...I was just concerned. Looking forward to recieving the parts.

Many Thanks,
Jeff

beepbeep · 01-04-2006, 02:54 PM

JE's do have lot's of piston slap as they expand more than OEM stuff and thus have to be made smaller. Other than that, they are very good. I've never heard of turbo specific problems either. Ring seating shouldn't be affected by turbocharging?

cgarr · cgarr's Garage

im running my je's at .0015 to .002 and I thought that was tite , anything greater and I would get noise until it heats up.