ENGINE ISSUES - BIG END QUESTION

[rogersirs]

HI All

Advice required please with respect to the two bearing engine in my 35/36 Tourer.

Having just got my car running nicely late last year on the last run of the season I encountered a nasty issue involving lots of smoke and a nasty noise. lifting the head revealled deep gouges (front and rear) in the bore of number 4 cylinder and on removing the offending piston, I found that although the tab washer was intact, the retaining bolt was loose, the Gudgeon Pin had fretted a nice groove out of the bolt and released the pin to happily do its worst to the bore. This was dissapointing as I have evidence to suggest the engine had done less than 8000 miles since a rebuild by a previous owner.

Anyway, I obtained a replacement cylinder bock and a set of Tony Betts pistons, reground the block, fitted new valve guides/valves and put it all back together. All looks good and it starts and runs very well.  However, at high revs there is a noticeable rattle and so its back in the garage with the sump/filter removed. I can visually see no issues, the Crank and Camshaft have not been disturbed,  and there is no wear or movement apparent in the Big End White Metal bearings in the normal plane ie from a rotational aspect. However the ConRods can now be moved londitudinally quiet easily and on movement a tapping noise is apparent on at least two Rods when the end of the rod contacts the crank web. Measuring with a feeler gauge the end float/clearance is about 15 thou and with the gauge inserted no movement/noise is apparent.  On page A2-51 of the Woodrow Manual it states that "There should be adequate side clearance - up to 1/16 of an inch" so I am well within that figure. 

A further point of note; on the old pistons (traditional split skirt type) which I still have, the Gudgeon Pin is still stiff to insert and I note Woodrow talks about warming the pistons as part of the insertion process, while on the new pistons the pin slips in with ease and is almost a floating fit. This might explain why this issue is suddenly apparent as the crank and bearings are unchanged, but it may be that the old pistons expand more and would be just as loose when the engine is hot.    

So, sorry if the above is a bit of a ramble but:

1) Has anyone had this issue previously?
2) Is this longditudinal Rod movement likely to be the cause of the rattle or should I be looking elsewhere?
3) Is the clearance figure of 1/16" in Woodrow correct?
4) Should the Gudgeon Pin on the Slipper Pistons fit and move so easily? 
5) Can anyone recommend a way forward?

Thanks in advance!

[Hedd_Jones]

Certainly the rod having end float on the crank is perfectly normal. I've personally seen more that 1/16 in a worn engine that ran acceptably quiet.

[Stuart Giles]

Did you re-use the conrod which had the loose Gudgeon pin?

[Ray White]

I'm not sure you are looking in the right area. If you had developed a big end issue I think it would be more noticeable on the over run rather than under load or high revs.

[Reckless Rat]

You said in your post that you've had the block reground - does that mean you've had the top surface skimmed? If so you need to check the relation of the pistons to the block at TDC - they should ideally be .020" below the block to avoid problems with crank whip.

[Ray White]

You said in your post that you've had the block reground - does that mean you've had the top surface skimmed? If so you need to check the relation of the pistons to the block at TDC - they should ideally be .020" below the block to avoid problems with crank whip.

What I was thinking. Another possibly is different gudgeon pin height?

["Slack Alice" Simon]

Or something else entirely: we had a rattle apparent at higher revs, when coming back from Moreton.

There is a lot of endfloat in the fan top pulley, and the belt was a bit loose - the pulley floating back and forth caused the rattle.

[rogersirs]

Cheers Gents

My immediate thought was the big ends as they are essentially the only bits I disturbed, but it may be that the noise is nothing new but was masked by the previous issues. Being new to this world the Rod end float appeared large, but I have little experience with non pressure fed bearings so it’s reassuring that 15 thou is not excessive as other bearing clearances appear OK. 

In answer to the above, yes I did re-use the Con Rod, but checked that it was not worn and grip of the new Gudgeon Pin was OK. With respect to the block; as well as a reborn, it was refaced and the valve seats had inserts fitted on the exhaust and all were recut. However, the reface was minor and the piston deck clearance was checked prior to the head refit. 

I intend to check the Cam followers to ensure all are free, check the pulley clearances and then remove the nose cone to check End floats and pinion clearances unless anyone can recommend anything else!

["Slack Alice" Simon]

How high is "high revs", when the rattle sets in?

[rogersirs]

Cheers, the issue is sorted. In replacing the fan belt I obviously altered alignment as with yours. The fan pulley was well past it and moving loosely in all directions, so replaced it. I should have had more confidence in my abilities and not immediately doubted my last maintenance activities.