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Mine Are Loose Too

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eschrom

Well-Known Member
Joined
Jan 18, 2006
Messages
939
Location
Manchester, PA
After reading about Boeingpilot's loose cylinder head studs I thought I should check mine, which have less than ten hours on them since installation. Sure enough, the two rearmost ones on the LH side were loose. Not finger loose but they budged when I applied torque. Hmmm... something else to keep an eye on.

Ed
GP 2276 with Mofoco 041 heads
 
They make thick wall 92's that fit in place of 94's (top and bottom). They have the thickest walls of any cylinders ever produced for Type 1 VWs. You trade a little performance for reliability.

Chucker
 
Eschrom , well there are 4 vw engines in my area that has this problem , so I'd check them , I've lost 3 heads due to this issue .
 
ED unfortunately every 5 hours, I just had to replace the left head after 2 hours of flying , seems its the head getting to hot but my cht's are below 400 on takeoff and about 325-350 in cruise. CHT is under the top 3rd stud nut.
 
Interesting findings. I have never had a head bolt get "loose". I have had them an 1/8 turn loose, but never anything major.

I am curious to know others torquing rituals. When assembling a motor, I torque them during the build. I run it for break in and torque them again. After the first flight I torque them again, then check them at 5 hours, then again at 10. Yearly after that.

Another consideration is what kind of head studs are being used. Cheap knock offs have a bad reputation for stretching. I am told that the stock VW studs are among the best.
 
Chucker,

The entire cooling system is different, so its hard to compare temps. I have a JPI gauge that uses bayonet style probes. I drilled pockets into the head near the exhaust ports. I was seeing CHT's around 375F while boosting to 35" durning part of the AVC race. Oil temps are hot at about 240F at that power setting. Hard to compare to the old engine since its a different cooler.

My head torque has been fine so far, but I have not checked it since the race. During the turbo upgrade, I spoke to a lot of people, one of them be Dan Diehl (of accessory case fame). He had turboed his KR2 at some point so I called him to pick his brain. His biggest issue was loose head studs. He had seen that aftermarket studs would stretch. He is the one that strongly encouraged me to use stock VW studs.

The turbo motor has about 25 hours on it now. I will not get a chance to inspect if for a few weeks, but I will let you know what I find.
 
Good information, Jeff. Thanks. I normally check mine after five to 10 hours and none has ever budged until now. Never got to do a yearly check because the heads have never been on that long between valve lappings but now that I'm using SS valves we'll see.

Ed
 
i bought all new 8mm studs nuts washers from jbugs and replaced the ld ones with these an still loose studs
 
Jeff,

90.5 mm heads have good wall thickness. They should hold their shape better than the 92's and are less prone to dig into the cylinder heads (and lose torque).

The VW stud suggestion sounds like good advice.

I neglected to ask. What is your compression ratio?

I am setting my engine up for a 5,000' MSL airport (KPRC). I plan on starting around 9.5:1. That may sound high, but when you account for density altitude, the chamber pressures will be no higher than an 8:1 engine at sea level....actually 7.9:1.

I have stock 8 mm studs and plan to use the thick wall 92 mm jugs.
 
So am I hearing this right, the 90.5 cylinders are thicker walled and will they fit in place where my 92 mm are without any machining of the heads and case, just a swap out. I know people are probably tired of me bringing this subject up but i'm looking at the safety aspect, I've lost 3 heads due to this.
 
I am not an engine person, but you got me reading. I found this:
Use 8mm head studs. New cases have case savers (Helicoils) built in, and these are far stronger than head studs threaded directly into the case. Use factory VW 8mm head studs (used are fine), since they expand and contract at the correct rate, and keep head torque constant. 10mm studs don’t do this, and that’s why 10mm stud engines have a problem with pulled studs. The VW factory changed to case savers and 8mm head studs in 1972 to solve this problem.
Link; http://www.aircooled.net/vw-performance-engines/

Not sure if this would address BoeingPilots problem.
Robin thanks for your list of cylinders. I was looking at what my little 1700 might be able to move up to.
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That is why I use 90.5's ; )

My CR was 9.5:1 before the turbo. It about 7.25:1 now.


Chucker said:
Jeff,

90.5 mm heads have good wall thickness. They should hold their shape better than the 92's and are less prone to dig into the cylinder heads (and lose torque).

The VW stud suggestion sounds like good advice.

I neglected to ask. What is your compression ratio?

I am setting my engine up for a 5,000' MSL airport (KPRC). I plan on starting around 9.5:1. That may sound high, but when you account for density altitude, the chamber pressures will be no higher than an 8:1 engine at sea level....actually 7.9:1.

I have stock 8 mm studs and plan to use the thick wall 92 mm jugs.
 
BoeingPilot said:
So am I hearing this right, the 90.5 cylinders are thicker walled and will they fit in place where my 92 mm are without any machining of the heads and case, just a swap out. I know people are probably tired of me bringing this subject up but i'm looking at the safety aspect, I've lost 3 heads due to this.

Yes! The 92's actually slip into what should be 90.5 holes. That is why the 92's are so thin. If you have thin wall 92's, you can make a simple upgrade (in reliability) by installing 90.5 jugs and pistons. I am going with thick wall 92's because:

1. I already had my pistons balanced, and
2. The 92 thick walls are even thicker than the 90.5's, and
3. I only have a 78mm stroke. I want the extra displacement.

The only down side is that I need to machine my heads to accept thicker cylinders. The jugs are necked at the base to fit a 90.5/92 case. However they are the same o.d. as 94mm cylinders on top. That is where the 4.5mm wall thickness really makes a difference.

My machine shop refuses to sell 92's. He will sell me 90.5's and he will sell me thick wall 92's. He won't sell the slip-in 92's.

Chucker
 
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