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Crankcase gasket / dowels

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Crankcase gasket / dowels

Posted by Andrew Wibmer at October 17. 2017

After reading Peters Hollands excellent article in the Roadholder back issues, I am getting ready to put my crankcases back together. Originally the case was separated with a wheatabix box gasket and some gold silicon crap, but I am not sure one is needed at all. I have taken care to finish the faces on a glass plate with grinding paste and now have a pretty good mating face. However the cylinder block mating face is about 6 thou out as is the Oil filter cover, both difficult to mate. Question is, can I leave out the dowels to get a better cylinder head match, and do I use a gasket or just wellseal. What have you chaps done?

 

Thanks

Andrew

Re: Crankcase gasket / dowels

Posted by robert_tuck at October 18. 2017

I have never been inside a lightweight but here goes. Cases can shuffle around in use so dowels are important, I would spend time in trying to determine exactly what is out . grease and leave gaskets overnight and then check gasket match with both halves ,remove dowels and ease diameter to allow trial runs with some dowels out. Rotating items need to be free.If everything else appart from dowels align then I would file the dowels as mistakes can be rectified by new dowels.

Re: Crankcase gasket / dowels

Posted by Andrew Wibmer at October 18. 2017

Previously robert_tuck wrote:

I have never been inside a lightweight but here goes. Cases can shuffle around in use so dowels are important, I would spend time in trying to determine exactly what is out . grease and leave gaskets overnight and then check gasket match with both halves ,remove dowels and ease diameter to allow trial runs with some dowels out. Rotating items need to be free.If everything else appart from dowels align then I would file the dowels as mistakes can be rectified by new dowels.

Thanks Robert, point taken about shuffling cases. Keen to know if gasket is required on mating faces of crankcase, seems to be some differences of opinion here. I rather thought I would use welseal and a thread for the mating faces of the case, and gaskets for the block and oil filter cover, but 6 odd thou seems to be quite a lip, jointing compound to take up that seems a but of a bodge. Interesting to know how others have tackled this. I doubt my case is the only "rough" one.

Andrew

Re: Crankcase gasket / dowels

Posted by Bob Matthews at October 18. 2017

I'm not sure if your crankcase faces do need a gasket but on all the engines I have re-built I have only used wellseal and never a gasket.

Are you sure they are a matching pair of crankcases?  Just wondering why someone would have used a very thick Weetabix gasket.

Re: Crankcase gasket / dowels

Posted by peter_holland1 at October 18. 2017

Hi Andrew,

I also noticed that the crankcase faces were not aligned on the cylinder mounting face. Here's what worked for me.

Have the 12 cylinder head studs in place.

No gasket, just jointing compound between the crankcase faces.

Crankshaft assembly installed. Put in every bolt securing crankcases together, tighten, and back off 1/4 to 1/2 turn.

Now put the cylinder, dry, onto the crankcase halves. Then the cylinder heads, dry no gasket. The cylinder heads could be replaced by spacers which you can see in the picture on the RH back issue.

Tighten down the cylinder head nuts (with the proper thick washers) which should bring the crankcase halves up to the cylinder base, forcing alignment on the cylinder mounting face. Crankcase dowels will conform. Check this is true by checking gap/no gap between cylinder base and crankcase halves. Now nip up the crankcase securing screws and gradually release the cylinder nuts. Keep an eye that the 6 thou hasn't returned.

Remove the cylinder and tighten the countersunk bolt between the cylinder liners.

Job done.

Good luck. Peter

BTW I did similar when tightening the heads down. Use the inlet manifold without a gasket and nipped up, also the head steady. Then you know that the two inlet manifold faces are in line, and the inlet tracts concentric as you tighten the head nuts down.

Re: Crankcase gasket / dowels

Posted by Andrew Wibmer at October 18. 2017

Previously Bob Matthews wrote:

I'm not sure if your crankcase faces do need a gasket but on all the engines I have re-built I have only used wellseal and never a gasket.

Are you sure they are a matching pair of crankcases?  Just wondering why someone would have used a very thick Weetabix gasket.

Thanks Bob, wellseal it is going to be. I am happy they are matching cases as the numbers are right and look ok, the weetabix box gasket was in line with a few other things I found in the engine but nothing too dreadful, just happy it didn't start when I bought it. I have decided to do the best I can to bring the block faces together, then remove as much material as I need to at the sump plate (oil filter) face. I can see the end float was too great as one of the crank bearings had spun on the crankshaft, not much but enough. Currently looking to keep the current 35 thou end float down to about 15 with shim. Heaven knows what it was like with a thick gasket. Interesting though..

Re: Crankcase gasket / dowels

Posted by Andrew Wibmer at October 18. 2017

Previously peter_holland1 wrote:

Hi Andrew,

I also noticed that the crankcase faces were not aligned on the cylinder mounting face. Here's what worked for me.

Have the 12 cylinder head studs in place.

No gasket, just jointing compound between the crankcase faces.

Crankshaft assembly installed. Put in every bolt securing crankcases together, tighten, and back off 1/4 to 1/2 turn.

Now put the cylinder, dry, onto the crankcase halves. Then the cylinder heads, dry no gasket. The cylinder heads could be replaced by spacers which you can see in the picture on the RH back issue.

Tighten down the cylinder head nuts (with the proper thick washers) which should bring the crankcase halves up to the cylinder base, forcing alignment on the cylinder mounting face. Crankcase dowels will conform. Check this is true by checking gap/no gap between cylinder base and crankcase halves. Now nip up the crankcase securing screws and gradually release the cylinder nuts. Keep an eye that the 6 thou hasn't returned.

Remove the cylinder and tighten the countersunk bolt between the cylinder liners.

Job done.

Good luck. Peter

BTW I did similar when tightening the heads down. Use the inlet manifold without a gasket and nipped up, also the head steady. Then you know that the two inlet manifold faces are in line, and the inlet tracts concentric as you tighten the head nuts down.

 

thanks Peter,

I had come across your description before but was not sure about the dowels, I can see now that they will conform as you say and should certainly be left in. Good tip about the same issue with the heads too. O would have missed that. My heads are the spigoted type but there is surely enough movement to allow the best fit I can get. It was your article "Forums and Leaky Lightweights" that has helped a huge amount. Many thanks for that.

Re: Crankcase gasket / dowels

Posted by andy_sochanik at October 27. 2017

Hi All,

Just to add my twopenneth.....

I have assembled two engines recently, having not used a crankcase gasket ever before as:

1) Most Gasket sets did NOT contain a crankcase gasket - though some DID!

2) The crankcase gasket (when present) was very thin.

3) I trusted Wellseal to glue the cases together, yet allow some shuffling.

I discovered that one of the engines nipped up one of the cams when fully tightened - so I created a gasket from proper gasket paper (have also used Corn Flakes in the past - but they wick oil) & reassembled - all was well.

Engine #2 went together without gasket paper - just Wellseal.

What was the difference in the two motors, I hear you ask? Well, dear listener - it was like this:

The engine that nipped up was NOT a matched pair of cases. There should be an identical stamp inside each case. That is, if '24' is stamped inside the left one, then you expect to find '24' inside its opposite half. Those of you whom I've bored with my photos in Roadholder in the last year will remember the non-matching numbers that I found. This  was further added to by the fact the top face was not machined to match its opposite half under the barrels. This engine is now assembled after the top face was milled to match both sides & a gasket added in between the two halves. It all rotates smoothly now.

Engine number two comprised a matched pair of cases, and was assembled using just Wellseal.

HTH....

Re: Crankcase gasket / dowels

Posted by Andrew Wibmer at October 27. 2017

Previously andy_sochanik wrote:

Hi All,

Just to add my twopenneth.....

I have assembled two engines recently, having not used a crankcase gasket ever before as:

1) Most Gasket sets did NOT contain a crankcase gasket - though some DID!

2) The crankcase gasket (when present) was very thin.

3) I trusted Wellseal to glue the cases together, yet allow some shuffling.

I discovered that one of the engines nipped up one of the cams when fully tightened - so I created a gasket from proper gasket paper (have also used Corn Flakes in the past - but they wick oil) & reassembled - all was well.

Engine #2 went together without gasket paper - just Wellseal.

What was the difference in the two motors, I hear you ask? Well, dear listener - it was like this:

The engine that nipped up was NOT a matched pair of cases. There should be an identical stamp inside each case. That is, if '24' is stamped inside the left one, then you expect to find '24' inside its opposite half. Those of you whom I've bored with my photos in Roadholder in the last year will remember the non-matching numbers that I found. This  was further added to by the fact the top face was not machined to match its opposite half under the barrels. This engine is now assembled after the top face was milled to match both sides & a gasket added in between the two halves. It all rotates smoothly now.

Engine number two comprised a matched pair of cases, and was assembled using just Wellseal.

HTH....

 

Happily mine are both numbered 130. However when pinching up as per Peter's instruction, I could get the Block faces to match but the Oil filter faces were grim, work with a file and block needed to get any where near right. Re gasket, I appreciate that we have all used inappropriate materials for gaskets, but the crank case one is a pain to replace so better to get it right first time. Also, given the entertainment I have had repairing spun bearings and the like, the implications of an extra 20 thou (measured from squished cornflake box) have on the crankshaft bearings and gearbox (kickstart end float) plus any others I have not identified, make this one to get right. Mismatched crankcases must create a few challenges in an entirely new sphere - one I hope not to visit. Though I am most impressed that they worked at all. Perhaps the tales we read of standards of work etc are rather overplayed. In fact I am amazed at how good the work was given the pressures / investment and worn machinery. Great fun and very interesting projects to work with.

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